Christoph Hader

Interests

Research

Laminar-turbulent boundary-layer transition (transonic, supersonic, hypersonic)High Performance ComputingNumerical MethodsHypersonic flowSupersonic flowFlow control for low and high-speed flowsTransition modelling for Reynolds Averaged Navier-Stokes (RANS) codesDirect Numerical SimulationsNonlinear physical mechanisms relevant for laminar-turbulent boundary-layer transition

Teaching

Laminar-turbulent boundary-layer transition (transonic, supersonic, hypersonic)High Performance ComputingNumerical MethodsHypersonic flowSupersonic flowDirect Numerical Simulations

Courses

Scholarly Contributions

Chapters

• Hader, C., & Fasel, H. F. (2022). Direct Numerical Simulations (DNS) of Natural Transition in High-Speed Boundary Layers Using a Broadband Random Forcing Approach. In IUTAM Laminar-Turbulent Transition(pp 565--574). Springer.

Journals/Publications

• Barraza, B., Gross, A., Hader, C., & Fasel, H. F. (2025). Hypersonic Transition Model for Second-Mode Instability. Journal of Spacecraft and Rockets, 62(6), 2007--2018.
• Barraza, B., Gross, A., Leinemann, M., Hader, C., & Fasel, H. F. (2025). Neural Network-Based Hypersonic Crossflow Transition Model. Journal of Spacecraft and Rockets, 62(2), 372--385.
• Barraza, B., Gross, A., Leinemann, M., Hader, C., & Fasel, H. F. (2025). Neural Network-Based Hypersonic Crossflow Transition Model. Journal of Spacecraft and Rockets, 62(Issue 2). doi:10.2514/1.a35975
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  A model is proposed for predicting crossflow transition in hypersonic flows. The model is based on transport equations for the crossflow amplification factor and a modified intermittency. The instability onset is estimated with a correlation function. The form of the transport equations is identical to that of typical transport equations for Reynolds-averaged Navier–Stokes (RANS) turbulence models, thus facilitating an easy integration into existing RANS codes. The crossflow amplification factor is estimated from local flow quantities using a neural network. The neural network is trained with a comprehensive database of linear stability theory data. The sensitivity of the amplification factor growth rate prediction to different dimensionless input parameters is evaluated. The input parameters that provide the most-accurate growth rate predictions are selected for the final form of the model. Based on the volume of the training data set, the model is expected to perform reliably for Mach numbers between 5 and 11 and within given upper bounds of the stagnation temperature and pressure. The model is validated for the HiFiRE-5 geometry, a circular cone at angle of attack, and a blunt swept flat plate. The amplification factor distributions obtained from the model are in good agreement with experimental data and linear stability analysis results.
• Hader, C., & Fasel, H. F. (2025). Delay of the Hot Streak Development for a Flared Cone at Mach 6. Journal of Spacecraft and Rockets, 1--19.
• Hader, C., & Fasel, H. F. (2025). Delay of the Hot Streak Development for a Flared Cone at Mach 6. Journal of Spacecraft and Rockets, 62(Issue 5). doi:10.2514/1.a36127
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  Direct numerical simulations were carried out in order to explore flow control using steady blowing and suction (control) strips at the wall of a flared cone at Mach 6. The flared cone geometry and the flow conditions of the experiments in the Boeing/AFOSR Mach 6 Quiet Tunnel at Purdue University were used for the numerical investigations. The objective of the flow control strategy was to delay or mitigate the negative consequences associated with the nonlinear transition stages, such as the “overshoots” of skin friction and heat transfer and the development of “hot” streaks, which have been previously observed in experiments and simulations. A parameter study on the influence of the steady blowing and suction strips on the fundamental resonance revealed the most effective location and strength of the control strips to attenuate the growth rate of the secondary disturbance waves. Applying one control strip in a fundamental breakdown simulation resulted in significant delay of the “hot” streak development on the surface of the cone. With an additional blowing and suction strip, the streak onset was delayed so that they were no longer observable in the entire computational domain. The research demonstrates that a detailed understanding of the nonlinear stages of transition can inform the development of effective flow control methods. The presented flow control method is specific to a second-mode-dominated transition scenario (fundamental breakdown).
• Barraza, B., Gross, A., Leinemann, M., Hader, C., & Fasel, H. F. (2024). Neural Network-Based Hypersonic Crossflow Transition Model. Journal of Spacecraft and Rockets, 1--14.
• Barraza, B., Groß, A., Leinemann, M., Hader, C., & Fasel, H. F. (2024). Transition Model for Second Mode and Crossflow Instabilities in Hypersonic Flow. AIAA SCITECH 2024 Forum. doi:10.2514/6.2024-2189
• Haas, A. P., Hader, C., & Fasel, H. F. (2024). Effects of Small Leading-Edge Bluntness on High-Speed Boundary-Layer Instabilities on Flat Plates. AIAA journal, 62(1), 162--174.
• Hader, C., & Fasel, H. (2024). Transition delay in a Mach 6 boundary layer using steady blowing and suction strips. Journal of Fluid Mechanics, 991. doi:10.1017/jfm.2024.468
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  Direct numerical simulations (DNS) were carried out to investigate flow control for transition delay using steady blowing/suction strips at the wall of a flared cone at Mach 6 and zero angle of attack. For the numerical investigations of the transition control strategy, the flared cone geometry and the flow conditions of the experiments in the Boeing/Air Force Office of Scientific Research (AFOSR) Mach 6 Quiet Tunnel (BAM6QT) at Purdue University were chosen. For the DNS, transition was initiated by introducing random disturbances at the inflow of the computational domain, emulating ‘natural’ transition in wind-tunnel experiments caused by free-stream noise. In both wind-tunnel experiments and numerical simulations, streamwise ‘hot’ streaks were found on the surface of the flared cone, which are caused by a nonlinear interaction of an axisymmetric second-mode wave and a pair of oblique waves of the same frequency (‘fundamental resonance’). The objective of the flow control strategy proposed here is to delay the transition onset, and thus mitigate the negative consequences associated with the nonlinear transition stages, i.e. the development of hot streaks and large wall-pressure amplitudes that were observed in experiments and DNS. Our previous so-called ‘controlled’ transition simulations have shown that flow control using steady blowing and suction strips can lead to a significant delay of the hot streak development on the surface of the flared cone. The simulation results presented in this paper show that this flow control strategy remains effective, even in a natural transition scenario characterized by broadband disturbances.
• Stemmer, C., Chiapparino, G., Bur, R., Lugrin, M., Little, J. C., Fasel, H. F., Tsakagiannis, V., Singh, A., Hader, C., & Threadgill, J. (2024). Scaling and Transition Effects on Hollow-Cylinder/Flare Shock/Boundary-Layer Interactions in Wind Tunnel Environments. AIAA Journal. doi:10.2514/1.J064261
• Threadgill, J., Hader, C., Singh, A., Tsakagiannis, V., Fasel, H. F., Little, J. C., Lugrin, M., Bur, R., Chiapparino, G., & Stemmer, C. (2024). Scaling and Transition Effects on Hollow-Cylinder/Flare Shock/Boundary-Layer Interactions in Wind Tunnel Environments. AIAA Journal, 1--14.
• Hader, C., & Fasel, H. F. (2023). Numerical Investigations of Nonlinearly Generated Disturbance Waves in High-Speed Boundary Layers. AIAA Journal, 61(11), 4797--4807.
• Woodward, M., Tian, Y., Lin, Y. T., Hader, C., Fasel, H., & Livescu, D. (2023). Mori-Zwanzig Modal Decomposition. arXiv preprint arXiv:2311.09524.
• Woodward, M., Tian, Y., Lin, Y. T., Hader, C., Fasel, H., Chertkov, M., & Livescu, D. (2023). Modal Analysis with Mori-Zwanzig Formalism: Application to Hypersonic Boundary Layer Flow. Bulletin of the American Physical Society.
• Hartman, A. B., Hader, C., & Fasel, H. F. (2021). Nonlinear transition mechanism on a blunt cone at Mach 6: oblique breakdown. Journal of Fluid Mechanics, 915, R2.
• Meersman, J. A., Hader, C., & Fasel, H. F. (2021). Numerical Investigation of Nonlinear Boundary-Layer Transition for Cones at Mach 6. AIAA Journal, 59(6), 1940--1952.
• Hader, C., & Fasel, H. F. (2020). Three-dimensional wave packet in a Mach 6 boundary layer on a flared cone. Journal of Fluid Mechanics, 885.
• Hartman, A. B., Hader, C., & Fasel, H. F. (2020). Correction: Numerical Investigation of Nonlinear Entropy-Layer Instability Waves for Hypersonic Boundary-Layers. AIAA AVIATION 2020 FORUM. doi:10.2514/6.2020-3085.c1
• Chynoweth, B. C., Schneider, S. P., Hader, C., Fasel, H., Batista, A., Kuehl, J., Juliano, T. J., & Wheaton, B. M. (2019). History and progress of boundary-layer transition on a Mach-6 flared cone. Journal of Spacecraft and Rockets, 56(2), 333--346.
• Hader, C., & Fasel, H. F. (2019). Direct Numerical Simulations of Hypersonic Boundary-Layer Transition for a Flared Cone: Fundamental Breakdown. Journal of Fluid Mechanics, 869.
• Hader, C., & Fasel, H. F. (2019). Direct numerical simulations of hypersonic boundary-layer transition for a flared cone: fundamental breakdown. Journal of Fluid Mechanics, 869, 341--384.
• Hader, C., & Fasel, H. F. (2018). Towards simulating natural transition in hypersonic boundary layers via random inflow disturbances. Journal of Fluid Mechanics, 847, R3.
• Hader, C., & Fasel, H. F. (2018). Towards simulating natural transition in hypersonic boundary layers via random inflow disturbances. Journal of Fluid Mechanics, 847.
• Brehm, C., Hader, C., & Fasel, H. F. (2015). A locally stabilized immersed boundary method for the compressible Navier--Stokes equations. Journal of Computational Physics, 295, 475--504.

Proceedings Publications

• Hader, C., & Fasel, H. (2025). Direct Numerical Simulation of Second-Mode Oblique Breakdown in a Mach 6 Sharp Cone Boundary Layer. In AIAA SCITECH 2025 Forum.
• Hader, C., & Fasel, H. (2025). Numerical Investigation of Boundary-Layer Transition on a Sharp Cone at Mach 10. In AIAA AVIATION FORUM AND ASCEND 2025.
• Hader, C., & Fasel, H. F. (2025). Direct Numerical Simulation of Second-Mode Oblique Breakdown in a Mach 6 Sharp Cone Boundary Layer. In AIAA Science and Technology Forum and Exposition, AIAA SciTech Forum 2025.
  More info

  Direct Numerical Simulations (DNS) were carried out to investigate the laminar-turbulent boundary-layer transition process for a 7◦ half-angle cone with a circular cross-section and a sharp nose at Mach 6 and zero angle of attack. The cone geometry and the flow conditions of experiments in the Boeing/AFOSR Mach 6 Quiet Tunnel (BAM6QT) at Purdue University were used for the numerical investigations. Linear Stability Theory (LST) analysis revealed that while axisymmetric second-mode waves are the dominant primary instability, shallow second-mode waves also experience strong amplification. Consequently, the role of second-mode oblique breakdown was explored by introducing a pair of oblique second-mode waves at low amplitudes. The disturbance development in downstream direction and the laminar to turbulent transition process is investigated. It is shown how the disturbance wave spectrum is filled up due to nonlinear interactions and which flow structures arise and how these structures locally break down to small scales. The skin friction initially follows the laminar trend, then exhibits a slight rise, dips back toward laminar levels, and subsequently increases toward turbulent values. A significant difference between the second mode oblique breakdown and previously investigated fundamental breakdown is the much reduced “overshoot” of the turbulent values of skin-friction and Stanton number in the transitional region. The DNS data clearly demonstrate that second mode oblique breakdown can lead to laminar-turbulent transition and therefore may be arelevant mechanism for transition in hypersonic cone boundary layers at Mach 6.
• Hader, C., & Fasel, H. F. (2025). Numerical Investigation of Boundary-Layer Transition on a Sharp Cone at Mach 10. In AIAA AVIATION FORUM AND ASCEND, 2025.
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  Numerical investigations were carried out to explore the linear and nonlinear stability regimes for boundary layers on a straight (right) cone with a 7◦ opening half-angle and a “sharp” nose tip at Mach 10 and zero angle of attack. The cone geometry of the experiments in the Arnold Engineering Development Complex (AEDC) Hypervelocity Wind Tunnel No. 9 (Tunnel 9) is used for the numerical investigations. Primary instability calculations using Linear Stability Theory (LST) exhibit unstable first, second, and third mode waves. For the investigated flow conditions and geometry the axisymmetric second mode disturbances are the dominant primary (linear) instability. Primary wave saturation calculations including transition onset were carried out in order to investigate the possibility to align transition onset in the simulations with that observed in the experiments. By varying the forcing amplitude of the axisymmetric second mode waves a range of frequencies was identified for which transition onset obtained in simulations and observed in experiments can be aligned. Secondary instability investigations, focusing on the so-called fundamental resonance, were carried out for the primary wave frequencies identified in the transition onset simulations. The results showed that the fundamental resonance is indeed a viable nonlinear mechanism that may be responsible for transition in the AEDC T9 experiments. Based on the primary and secondary instability calculations high-resolution “controlled” transition simulations were carried out and demonstrate that fundamental breakdown can lead to sustained turbulent flow. The Stanton number development observed in experiments shows slight differences compared to that obtained in the controlled transition simulations.
• Holt, A., Hader, C., & Fasel, H. (2025). Numerical Investigation of the Linear and Nonlinear Transition Stages for a Sharp Cone at Mach 14. In AIAA AVIATION FORUM AND ASCEND 2025.
• Holt, A., Hader, C., & Fasel, H. F. (2025). Numerical investigation of the linear and nonlinear transition stages for a sharp cone at Mach 14. In AIAA AVIATION FORUM AND ASCEND, 2025.
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  Numerical investigations were carried out to explore the linear and nonlinear stability regimes for boundary layers on a straight (right) cone with a 7◦ opening half-angle and a “sharp” nose tip at Mach 14 and zero angle of attack. The cone geometry of the experiments in the Arnold Engineering Development Complex (AEDC) Hypervelocity Wind Tunnel No. 9 (Tunnel 9) was used for the numerical investigations. The flow conditions corresponding to the “sharp” cone experiments carried out at the T9 facility were considered. The primary instability regime was explored using Linear Stability Theory (LST) and revealed unstable first, second and third mode waves. The axisymmetric second mode waves are the dominant primary instability. Primary wave saturation calculations were carried out for a range of frequencies that resulted in substantial N-factors near the transition onset location observed in the experiments. These investigations were used to adjust the forcing amplitudes of the primary waves such that transition onset in the simulations aligns approximately with that observed in the experiments. Based on the primary instability and primary wave saturation calculations, secondary instability calculations investigating the so-called fundamental resonance were carried out. These investigations confirmed that a strong fundamental resonance is present for the investigated flow conditions and geometry, therefore making this a viable mechanism that might lead to transition in the experiments. Based on the primary and secondary instability investigations, high-resolution “controlled” transition simulations have been set up and are currently underway.
• Perez, H., Hader, C., & Fasel, H. (2025). Numerical Investigation of Laminar-Turbulent Boundary-Layer Transition for an Ogive Geometry at Mach 7: Wind Tunnel and Flight Conditions. In AIAA AVIATION FORUM AND ASCEND 2025.
• Perez, H., Hader, C., & Fasel, H. F. (2025). Numerical Investigation of Laminar-Turbulent Boundary-Layer Transition for an Ogive Geometry at Mach 7: Wind tunnel and Flight Conditions. In AIAA AVIATION FORUM AND ASCEND, 2025.
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  Numerical investigations were carried out for an ogive geometry with a blunted nose tip at zero angle of attack for atmospheric flight conditions at M = 7.1. These investigations are compared to those for the flow conditions of the hypersonic wind tunnel (H2K) experiments conducted by the German Aerospace Center (DLR), also at M = 7.1. For this comparison, the Mach and unit Reynolds numbers for both flight and wind tunnel conditions are the same allowing for a direct comparison of how a change from wind tunnel to flight conditions affects the linear and nonlinear transition regimes. Linear Stability Theory (LST) calculations revealed that while both first and second mode waves experience significant amplification under wind tunnel conditions, only second mode waves are present under flight conditions. Similar to the investigations for the wind tunnel conditions, primary wave saturation and transition onset calculations were carried out for the flight conditions to determine whether large amplitude second mode waves can reach amplitudes sufficient for transition onset. Secondary instability calculations showed that the so-called fundamental resonance leads to strong secondary amplification, making this a relevant mechanism that could lead to transition for the ogive geometry under atmospheric flight conditions. Based on the primary and secondary instability investigations, high-resolution "controlled" transition simulations have been set up and are currently underway.
• Tsakagiannis, V., Hader, C., & Fasel, H. (2025). Controlled Transition Simulations on an Axisymmetric 8-Degree Compression Ramp at Mach 5. In AIAA AVIATION FORUM AND ASCEND 2025.
• Tsakagiannis, V., Hader, C., & Fasel, H. (2025). Numerical investigations of the linear stability regime for a separation bubble on an Axisymmetric Compression Ramp at Mach 5. In AIAA SCITECH 2025 Forum.
• Tsakagiannis, V., Hader, C., & Fasel, H. F. (2025). Controlled Transition Simulations on an Axisymmetric 8-Degree Compression Ramp at Mach 5. In AIAA AVIATION FORUM AND ASCEND, 2025.
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  Numerical investigations are conducted to investigate the transitional shock-boundary-layer interaction (SBLI) on a hollow cylinder flare geometry at Mach 5. The flow conditions are matched as closely as possible to those used in experiments at the Mach 5 Ludwieg Tube (LT5) at the University of Arizona (UA). A variation of the geometry used in the experiments was used for the numerical simulations with a flare angle of 8◦. This case was previously identified as only convectively unstable, with no signs of an absolute/global instability. The linear regime is investigated using local linear stability theory (LST) and low amplitude controlled forcing simulations. An oblique 1st mode/shear-layer mode is found to be amplified for a range of azimuthal wavenumbers. Subsequently, highly resolved direct numerical simulations (DNS) are performed in order to investigate the possibility of an oblique breakdown scenario, dominated by the 1st mode/shear-layer mode. Contours of the azimuthal averaged skin friction over time, show that the separation region for the transitional flow contracts compared to the laminar base flow. Pressure amplitude spectra show the amplification of the nonlinearly generated signature modes, consistent with an oblique breakdown scenario. Time averaged skin-friction coefficient and Stanton number, and their Fourier transformed amplitudes, indicate the formation of streaks that appear already inside the separation bubble. Towards the end of the computational domain, smaller structures can be observed in the instantaneous pseudo-Schlieren contours visualizations indicating that the late nonlinear stages of the transition process have been reached.
• Tsakagiannis, V., Hader, C., & Fasel, H. F. (2025). Numerical investigations of the linear stability regime for a separation bubble on an Axisymmetric Compression Ramp at Mach 5. In AIAA Science and Technology Forum and Exposition, AIAA SciTech Forum 2025.
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  Numerical investigations were carried in order to investigate the transitional shock boundary-layer interaction (SBLI) on a hollow cylinder flare geometry at Mach 5. The geometry and flow conditions were matched, as closely as possible, to those in the experiments at the Mach 5 Ludwieg Tube (LT5) at the University of Arizona (UA). In the literature, different mechanisms have been proposed to play a role in the transition process of the separated region of the SBLI, such as the shear layer as the the Görtler instability. Our previous results for low amplitude three-dimensional wave packets and various flare angles, showed evidence that both these mechanisms are present in the simulations. Estimations of the Görtler number along a streamline, showed that for all the flare angles investigated the flow is highly unstable with respect to the Görtler instability. Additionally, estimates available in the literature regarding the azimuthal wavenumber corresponding to the Görtler vortices match reasonably well with results from the wave packets. For the shear layer instability, a good match is obtained between local LST and low amplitude controlled forcing simulations.
• Woodward, M., Lin, Y. T., Hader, C., Fasel, H. F., & Livescu, D. (2025). Mori--Zwanzig Mode Decomposition: a comparison to DMD and HODMD. In Division of Fluid Dynamics Annual Meeting 2025.
• Barraza, B., Barraza, B., Gross, A., Gross, A., Hader, C., Hader, C., Fasel, H. F., & Fasel, P. (2024). Hypersonic Transition Model for Second Mode and Crossflow Instabilities. In AIAA AVIATION FORUM AND ASCEND 2024.
• Barraza, B., Barraza, B., Gross, A., Gross, A., Leinemann, M., Leinemann, M., Hader, C., Hader, C., Fasel, H. F., & Fasel, H. (2024). Transition Model for Second Mode and Crossflow Instabilities in Hypersonic Flow. In AIAA SCITECH 2024 Forum.
• Hader, C., & Fasel, H. (2024). Numerical Investigation of Hypersonic Boundary-Layer Transition for an Ogive Geometry. In AIAA SCITECH 2024 Forum.
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  Numerical investigations were carried out for an ogive geometry with a blunted nose-tip for the flow conditions of the hypersonic wind tunnel (H2K) experiments of the German Aerospace Center (DLR) at Mach 5.3 and Mach 7. Linear Stability Theory (LST) was employed to analyze the primary instability regime. The LST results indicated amplification of both first and second mode waves. Specifically, second mode waves exhibited higher growth rates than first mode waves for both Mach numbers, while the N-factors were larger for first mode waves at M = 5.3. Based on the LST findings, the feasibility of various “controlled” transition scenarios was explored, with particular focus on first mode oblique breakdown. Simulation results for both Mach numbers demonstrated progression to the late nonlinear stages and an advancement of the boundary-layer toward fully developed turbulent flow. The forcing amplitudes for oblique first mode waves for the “controlled” transition DNS were determined to approximately align the transition onset in the simulations the with experimental transition onset locations. These investigations suggest that a first mode-dominated oblique breakdown may be a viable nonlinear mechanism for transition for the investigated geometry and wind tunnel conditions.
• Hader, C., & Fasel, H. (2024). Numerical investigation of the linear and nonlinear transition stages for a sharp cone at Mach 10. In AIAA AVIATION FORUM AND ASCEND 2024.
  More info

  Numerical investigations were carried out to explore the linear and nonlinear stability regimes for boundary layers on a straight (right) cone with a 7◦ opening half-angle and a “sharp” nose tip at Mach 10 and zero angle of attack. The cone geometry and flow conditions of the experiments in the Arnold Engineering Development Complex (AEDC) Hypervelocity Wind Tunnel No. 9 (Tunnel 9) is used for the numerical investigations. Two unit Reynolds numbers, corresponding to the “sharp” cone experiments carried out at the T9 facility, are considered. Primary instability calculations using Linear Stability Theory (LST) confirmed that the linear amplification rates and the corresponding N-factors increase with increasing unit Reynolds numbers as expected. For all investigated cases the axisymmetric second mode disturbances are the dominant primary (linear) instability. Subsequent primary wave saturation calculations including transition onset were carried out in order to investigate the possibility to align transition onset in the simulations with that observed in the experiments. By varying the forcing amplitude of the axisymmetric second mode waves a range of frequencies was identified for which transition onset obtained in simulations and observed in experiments can be aligned. Subsequent secondary instability investigations, focusing on the so-called fundamental resonance, were carried out for the primary wave frequencies identified in the transition onset simulations. The results showed that the fundamental resonance is indeed a viable nonlinear mechanism that may be responsible for transition in the AEDC T9 experiments. The numerical investigations showed that larger unit Reynolds numbers do not only result in increased growth rates for the linear (primary) instability but also in a stronger secondary instability.
• Hader, C., & Fasel, H. F. (2024). Numerical Investigation of Hypersonic Boundary-Layer Transition for an Ogive Geometry. In AIAA SciTech 2024 Forum.
• Hader, C., & Fasel, H. F. (2024). Numerical Investigation of the Linear and Nonlinear Transition Stages for a Sharp Cone at Mach 10. In AIAA AVIATION FORUM AND ASCEND 2024.
• Ramesh, R., Ramesh, R., Skora, A., Skora, A., Hader, C., Hader, C., Fasel, H. F., Fasel, H., Craig, S. A., & Craig, S. (2024). Experimental Measurements of Hypersonic Boundary Layer Transition on the STORT Ogive Geometry. In AIAA Aviation Forum And Ascend 2024.
• Surujhlal, D., Wagner, A., Hader, C., & Fasel, H. (2024). Hot streak development in hypersonic boundary layer transition on a blunt cone with cooled walls: shock tunnel experiments and numerical simulations. In IUTAM Laminar-Turbulent Transition: 10th IUTAM Symposium.
• Threadgill, J., Hader, C., Singh, A., Tsakagiannis, V., Fasel, H., Little, J., Lugrin, M., Bur, R., Chiapparino, G., & Stemmer, C. (2024). Scaling and Transition Effects on Hollow-Cylinder/Flare SBLIs inWind Tunnel Environments. In AIAA SCITECH 2024 Forum.
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  A comprehensive investigation into the flow over a Hollow-Cylinder/Flare has been conducted at Mach 5 with ReL ≈ 11×105 and a flare deflection θ = 15◦. Experiments of two similar models have been conducted in LT5 at the University of Arizona (Tucson, USA) and R2Ch at ONERA (Meudon, France). Despite similar non-dimensional scaling of the models, a considerable difference in reattachment behavior was observed from Infrared Thermography measurements, indicating that the reattachment in LT5 was located approximately twice as far from the flare base as observed in R2Ch. This discrepancy has driven the investigation in an attempt to identify the cause of this difference. Simulations have been performed at the University of Arizona, ONERA, and the Technical University of Munich (Germany) in support of this study, targeting a range of potential factors that are relevant to the challenge, to quantify the various influences. Amongst the effects reviewed are: differences in the freestream Mach number (M∞) modulating boundary layer development and the flare-induced inviscid pressure rise, differences in the wall temperature conditions (Tw/T0) also affecting boundary layer development, 3D relief effects due to different normalized cylinder diameters (D/L), differences in the bluntnesses of the two nominally sharp configurations (rnose/L), and the impact of freestream disturbances. The noise environment appears to play a significant role in scaling the Shock Boundary Layer Interaction (SBLI) by affecting the transition behavior along the separated shear layer and causing the bubble to grow/shrink to accommodate. Simulations show that the amplitude can be modulated to control the SBLI size, and produce a close match to the experimental results. However, the distribution of noise in the frequency spectra remains unclear. Experimental investigation of the respective noise environment between the two facilities showed that despite each tunnel exhibiting similar noise magnitudes (expressed as p′/p̄∞) they differed considerably in the range of frequencies (by a factor of 6.5 when considering freestream Strouhal number), suggesting additional parameters are required when quantifying wind tunnel freestream noise conditions beyond its simple amplitude. This study was conducted as part of an international collaborative effort in support of NATO STO AVT-346 Research Task Group.
• Tsakagiannis, V., Hader, C., & Fasel, H. (2024). Numerical investigations of laminar-turbulent transition for a hollow cylinder flare wind tunnel model at Mach 5. In AIAA SCITECH 2024 Forum.
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  Numerical investigations were carried in order to investigate the transitional shock boundarylayer interaction on a hollow cylinder flare geometry at Mach 5. The influence of the flare angle and the leading edge radius on the topology of the separation bubble was also investigated. The geometry and flow conditions are matched, as closely as possible, to those of the experiments in the Mach 5 Ludwieg Tube (LT5) at the University of Arizona (UA). Base flow calculations using various CFD codes carried out indicate that for the flow conditions and flare angles considered, a separation bubble develops downstream of the leading edge of the hollow cylinder. For relatively small flare angles a steady separation bubble is obtained. As the flare angle increases, the bubble topology becomes increasingly complex and “bubbles within the bubble” are observed. Additionally, it is shown that the bluntness of the leading edge, while keeping the flare angle constant, has an impact on the separation and reattachment locations, and subsequently on the size of the separated region. Calculations for low amplitude three-dimensional wave packets revealed that both axisymmetric and oblique waves are amplified while propagating downstream. Preliminary simulations employing a broadband forcing method, designed to emulate a “natural” transition scenario similar to wind tunnel experiments, confirm the presence of instabilities in the shear layer.
• Tsakagiannis, V., Hader, C., & Fasel, H. (2024). Numerical investigations of the linear and nonlinear transition stages for a hollow cylinder ŕare at Mach 5. In AIAA AVIATION FORUM AND ASCEND 2024.
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  Direct numerical simulations (DNS) were carried out in order to investigate the linear and nonlinear transition stages for a shock boundary layer interaction (SBLI) on a hollow cylinder ŕare geometry at Mach 5. The geometry and ŕow conditions are matched, as closely as possible, to those used in the experiments at the Mach 5 Ludwieg Tube (LT5) at the University of Arizona (UA). While for the experiments a 15◦ ŕare angle was used, for the numerical investigations several additional ŕare angles were considered. For the investigations presented in this paper łforced" and łunforced" simulations were carried out. For the łforced" simulations three-dimensional wave packets were introduced, that were generated by a short-duration pulse disturbance. The initial forcing amplitudes of the pulse disturbances were chosen to be small in order to assess the linear stability behavior. In addition to the łforced" simulations, łunforced" simulations were also carried out for all the ŕare angles considered, in order to explore if absolute/global instabilities are developing from the discretization and round off errors. The low amplitude wave packet simulations for different ŕare angles showed that the shear layer of the separation bubble is unstable with respect to axisymmetric and oblique traveling waves. For ŕare angles greater than 8◦ streamwise streaks developed near the reattachment location for both the forced and unforced simulations. A comparison between the forced and unforced simulations indicates that for the larger ŕare angles an absolute instability mechanism may be responsible for the streak development.
• Tsakagiannis, V., Hader, C., & Fasel, H. F. (2024).

  Numerical investigations of laminar-turbulent transition for a hollow cylinder flare at Mach 5

  . In AIAA Scitech 2024 Forum.
• Tsakagiannis, V., Hader, C., & Fasel, H. F. (2024). Numerical investigations of laminar-turbulent transition for a hollow cylinder flare at Mach 5. In AIAA SCITECH 2024 Forum.
• Tsakagiannis, V., Hader, C., & Fasel, H. F. (2024). Numerical investigations of the linear and nonlinear transition stages for a hollow cylinder flare at Mach 5. In AIAA AVIATION FORUM AND ASCEND 2024.
• Woodward, M., Tian, Y., Lin, Y. T., Hader, C., Fasel, H. F., & Livescu, D. (2024). Mori--Zwanzig Modal Decomposition: Applications and Analysis of Laminar-Turbulent Boundary Layer Transition. In AIAA AVIATION FORUM AND ASCEND 2024.
• Woodward, M., Tian, Y., Lin, Y. T., Hader, C., Fasel, H., & Livescu, D. (2024). Mori--Zwanzig Mode Decomposition: Transient Flows and Laminar-Turbulent Boundary Layer Transition. In AIAA Aviation Forum and ASCEND, 2024.
• Barraza, B., Gross, A., Haas, A. P., Hader, C., & Fasel, H. F. (2023). Machine-Learning-Based Transition Prediction for Hypersonic Boundary Layers with Crossflow. In AIAA SCITECH 2023 Forum.
• Barraza, B., Gross, A., Leinemann, M., Hader, C., & Fasel, H. F. (2023). Local Transition Model for Crossflow Instability in High-Speed Boundary-Layers. In AIAA AVIATION 2023 Forum.
• Flood, J. J., Hader, C., Skora, A., Fasel, H. F., & Craig, S. A. (2023). Experimental measurements and numerical investigations of boundary-layer instabilities on a Mach 5 hollow cylinder. In AIAA SCITECH 2023 Forum.
• Hader, C., & Fasel, H. F. (2023). Numerical investigation of the laminar-turbulent boundary-layer transition for a circular cone at Mach 5: wind tunnel and flight conditions. In AIAA SCITECH 2023 Forum.
• Hartman, A., Fasel, H. F., Wernz, S., Haas, A. P., & Hader, C. (2023). Numerical Investigations of Hypersonic Boundary-Layer Stability for a Blunt Flat Delta Wing. In AIAA AVIATION 2023 Forum.
• Leinemann, M., Haas, A. P., Hader, C., & Fasel, H. F. (2023). Direct Numerical Simulations of the Nonlinear Boundary Layer Transition Regime on a Blunt Swept Flat Plate at Mach 6. In AIAA AVIATION 2023 Forum.
• Singh, A., Hader, C., Threadgill, J. A., Fasel, H. F., & Little, J. C. (2023). Schlieren Visualization of Controlled Disturbances in Mach 5 Flow Over a Hollow Cylinder Flare. In AIAA SCITECH 2023 Forum.
• Woodward, M., Tian, Y., Lin, Y. T., Mohan, A. T., Hader, C., Fasel, H. F., Chertkov, M., & Livescu, D. (2023). Data-Driven Mori-Zwanzig: Reduced Order Modeling of Sparse Sensors Measurements for Boundary Layer Transition. In AIAA AVIATION 2023 Forum.
• Woodward, M., Tian, Y., Mohan, A. T., Lin, Y. T., Hader, C., Livescu, D., Fasel, H. F., & Chertkov, M. (2023). Data-Driven Mori-Zwanzig: Approaching a Reduced Order Model for Hypersonic Boundary Layer Transition. In AIAA SCITECH 2023 Forum.
• Bailey, M., Hader, C., & Fasel, H. F. (2022). Numerical Investigation of the Nonlinear Transition Stages in a High-Enthalpy Hypersonic Boundary Layer on a Right Cone. In IUTAM Laminar-Turbulent Transition: 9th IUTAM Symposium, London, UK, September 2--6, 2019.
• Barraza, B., Gross, A., Haas, A. P., Hader, C., & Fasel, H. (2022). Machine-Learning-Based Amplification Factor Transport Equation for Hypersonic Boundary-Layers. In AIAA AVIATION 2022 Forum.
• Biella, M., Hader, C., & Fasel, H. F. (2022). Numerical investigation of the laminar-turbulent transition process for the HIFiRE-1 Flight Test. In AIAA SCITECH 2022 Forum.
• Haas, A. P., Hader, C., & Fasel, H. F. (2022). Numerical Investigation of Cross-Flow Instability for a Supersonic Swept Wing with a Biconvex Airfoil. In AIAA SCITECH 2022 Forum.
• Hader, C., & Fasel, H. F. (2022). Direct Numerical Simulations (DNS) of Natural Transition in High-Speed Boundary Layers Using a Broadband Random Forcing Approach. In IUTAM Laminar-Turbulent Transition: 9th IUTAM Symposium, London, UK, September 2--6, 2019.
• Hader, C., & Fasel, H. F. (2022). Flow control using steady blowing and suction strips in a Mach 6 Boundary Layer on a Flared Cone: "Natural" Transition. In AIAA AVIATION 2022 Forum.
• Hader, C., & Fasel, H. F. (2022). Numerical Investigation of Boundary-Layer Transition for a slender cone at Mach 6 initiated with Random Disturbances. In AIAA SCITECH 2022 Forum.
• Hader, C., Subramanya, S. M., & Fasel, H. F. (2022). Direct Numerical Simulations of Laminar-Turbulent Transition for Transonic Boundary Layers initiated by Random Disturbances. In AIAA SCITECH 2022 Forum.
• Herman, B., Hader, C., & Fasel, H. F. (2022). Numerical investigation of the effects of wall heating and cooling on the nonlinear transition stages for a sharp cone at Mach 6. In AIAA Scitech 2022 Forum.
• Hurworth, A., Hader, C., & Fasel, H. F. (2022). Direct Numerical Simulations of Hypersonic Boundary-Layer Transition for a Sharp Cone at Mach 10. In AIAA SCITECH 2022 Forum.
• Leinemann, M., Hader, C., & Fasel, H. F. (2022). Numerical Investigation of Boundary-Layer Transition initiated by Random Disturbances for a Flat Plate at Mach 6. In AIAA SCITECH 2022 Forum.
• Little, J. C., Threadgill, J. A., Jouannais, L., Craig, S., Flood, J., Hader, C., Flood, J., Hader, C., Jouannais, L., Craig, S., Threadgill, J. A., & Little, J. C. (2022, January). Fin-induced Shock Boundary Layer Interactions on a Flat Plate and Hollow Cylinder at Mach 5. In AIAA SCITECH 2022 Forum, 21.
• Meersman, J. A., Hader, C., & Fasel, H. F. (2022). Numerical Investigation of Hypersonic Boundary-Layer Transition for an Ogive Cone. In AIAA SciTech 2022 Forum.
• Stevens, S., Hader, C., & Fasel, H. F. (2022). Numerical investigation of the nonlinear transition stages for a sharp cone at Mach 10. In AIAA Aviation 2022 Forum.
• Tsakagiannis, V., Hader, C., & Fasel, H. F. (2022). Nonlinear wave packet simulation for a cone at Mach 10 using a GPU accelerated pseudo-spectral scheme. In AIAA AVIATION 2022 Forum.
• Haas, A. P., Hader, C., & Fasel, H. F. (2021). Linear Stability Investigation of Cross-Flow Instability for a Supersonic Swept Wing with a Biconvex Airfoil. In AIAA Aviation 2021 Forum.
• Hader, C., & Fasel, H. F. (2021). Flow control using steady blowing and suction strips in a Mach 6 Boundary Layer on a Flared Cone. In AIAA Scitech 2021 Forum.
• Hader, C., Deng, N., & Fasel, H. F. (2021). Direct Numerical Simulations of Hypersonic Boundary-Layer Transition for a straight cone at Mach 5. In AIAA Scitech 2021 Forum.
• Hader, C., Deng, N., & Fasel, H. F. (2021). Direct numerical simulations of hypersonic boundary-layer transition for a straight cone at Mach 5. In AIAA Scitech 2021 Forum.
• Hader, C., Deng, N., Woodward, M., & Fasel, H. F. (2021). Direct Numerical Simulations of Laminar-Turbulent Transition for Transonic Boundary Layers. In AIAA Scitech 2021 Forum.
• Hader, C., Hader, C., Fasel, H. F., & Fasel, H. F. (2021). Three-dimensional wave packets in a Mach 10 Boundary Layer on a Sharp Cone. In AIAA Aviation 2021 Forum.
• Harder, A., Singh, A., Threadgill, J., Little, J., Hader, C., & Fasel, H. (2021). Investigation of Transitional SBLIs using Plasma Based Disturbances. In APS Division of Fluid Dynamics Meeting Abstracts.
• Hartman, A., Hader, C., & Fasel, H. F. (2021). Direct Numerical Simulations of laminar-turbulent boundary-layer transition for a blunt cone at Mach 6. In AIAA Scitech 2021 Forum.
• Hartman, A., Hader, C., & Fasel, H. F. (2021). Direct Numerical Simulations of laminar-turbulent boundary-layer transition for blunt cones at Mach 6: Effect of Varying Nose Bluntness. In AIAA AVIATION 2021 FORUM.
• Leinemann, M., Hader, C., & Fasel, H. F. (2021). Direct numerical simulations of the nonlinear boundary layer transition regime on a flat plate at Mach 6. In AIAA Scitech 2021 Forum.
• Meersman, J. A., Hader, C., & Fasel, H. F. (2021). Direct numerical simulations of nonlinear entropy-layer instability waves. In AIAA Scitech 2021 Forum.
• Singh, A., Threadgill, J. A., Flood, J. T., Craig, S. A., Little, J. C., Hader, C., & Fasel, H. F. (2021). Development of Plasma-based Controlled Disturbances for the Study of Boundary Layer Transition and Shock Boundary Layer Interaction. In AIAA Aviation 2021 Forum.
• Hader, C., & Fasel, H. F. (2020). Wave packets on a flared cone at Mach 6. In AIAA Scitech 2020 Forum.
• Hader, C., Leinemann, M., & Fasel, H. F. (2020). Direct Numerical Simulations of Hypersonic Boundary-Layer Transition for a slender cone. In AIAA Aviation 2020 Forum.
• Hartman, A., Hader, C., & Fasel, H. F. (2020). Numerical investigation of nonlinear entropy-layer instability waves for hypersonic boundary-layers. In AIAA AVIATION 2020 FORUM.
• Leinemann, M., Hader, C., & Fasel, H. F. (2020). Direct Numerical Simulations of the Nonlinear Transition Regime on a Flat Plate at Mach 6. In AIAA Scitech 2020 Forum.
• Chynoweth, B. C., Hader, C., Batista, A., Juliano, T. J., Kuehl, J., Wheaton, B. M., Fasel, H. F., & Schneider, S. P. (2018). A history and progress of second mode dominated boundary-layer transition on a Mach 6 flared cone. In 2018 AIAA Aerospace Sciences Meeting.
• Meersman, J. A., Hader, C., & Fasel, H. F. (2018). Hypersonic boundary-layer transition: comparison of the fundamental resonance breakdown for a flared and straight cone at Mach 6. In 2018 Fluid Dynamics Conference.
• Hader, C., & Fasel, H. F. (2017). Fundamental resonance breakdown for a flared cone at Mach 6. In 55th AIAA Aerospace Sciences Meeting.
• Hader, C., & Fasel, H. F. (2016). Laminar-turbulent transition on a flared cone at Mach 6. In 46th AIAA Fluid Dynamics Conference.
• Brehm, C., Barad, M. F., & Hader, C. (2014). A High-Order Immersed Interface Method for Compressible Flows. In 7th AIAA Theoretical Fluid Mechanics Conference.
• Brehm, C., Hader, C., & Fasel, H. (2014). A higher-order immersed boundary method for viscous compressible flows. In AIAA Theoretical Fluid Mechanics Conference, AIAA, 2093.
• Hader, C., Brehm, C., & Fasel, H. F. (2014). Numerical Investigation of transition delay for various controlled breakdown scenarios in a Mach 6 Boundary Layer using porous walls. In 7th AIAA Theoretical Fluid Mechanics Conference.
• Hader, C., Brehm, C., & Fasel, H. (2013). Numerical investigation of porous walls for a Mach 6.0 boundary layer using an immersed interface method. In 51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition.
• Hader, C., Brehm, C., & Fasel, H. F. (2013). Numerical Investigation of transition delay using porous walls. In 43rd AIAA Fluid Dynamics Conference.
• Brehm, C., Hader, C., & Fasel, H. (2012). Novel immersed boundary/interface method for the compressible navier-stokes equations. In 50th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition.
• Hader, C., & Fasel, H. (2011). Numerical investigation of porous walls for a Mach 6.0 boundary layer using an immersed boundary method. In 41st AIAA Fluid Dynamics Conference and Exhibit.

Presentations

• Little, J. C., Fasel, H. F., Hader, C., & Threadgill, J. (2024, August). Investigation of Transitional SBLI at Mach 5 using Controlled Forcing: Experiments, Simulations and Theory. ONR/AFOSR/ARO High-Speed Review. Minneapolis, MN: ONR/AFOSR/ARO.
• Little, J. C., Fasel, H. F., Hader, C., & Threadgill, J. (2024, October). Overview of On-Going Work and Future Plans for the Follow-On ET. NATO STO AVT 346 Fall Meeting. Koblenz, Germany: NATO.

Poster Presentations

• Hartman, A., Hader, C., & Fasel, H. F. (2024, September).

  Numerical Investigations of Stability and Transition for a Blunt Swept Flat Plate at Mach 10

  . IUTAM Transition 2024 IUTAM Symposium on Laminar-Turbulent Transition 2-6th September 2024 Nagano, Japan. Nagano, Japan.

Others

• Fasel, H. F., & Hader, C. (2024). Flow control techniques for delaying or accelerating laminar-turbulent boundary-layer transition for high-speed flight vehicles.
• Fasel, H. F., & Hader, C. (2021, December). Flow control techniques for delaying or accelerating laminar-turbulent boundary-layer transition for high-speed flight vehicles.
  More info

  patent application
• Hader, C. (2019, May). Direct Numerical Simulations of Hypersonic Boundary-Layer Transition for a Flared Cone.