Alex Craig

Interests

Research

Boundary-layer stability and transition, hydrodynamic instability, experimental fluid mechanics, hypersonic aerodynamics, aerodynamic heating

Teaching

Fluid Mechanics, Aerodynamics, Compressible Flow, Hydrodynamic Stability

Courses

Scholarly Contributions

Journals/Publications

• Bearden, K. P., Padilla, V. E., Taubert, L., & Craig, S. A. (2022). Calibration and performance characterization of a Mach 5 Ludwieg tube. Review of Scientific Instruments, 93(8). doi:10.1063/5.0093052
• Craig, S. A. (2022). Tip sharpness criterion for hypersonic wind tunnel experiments. AIAA Journal, 60(12). doi:10.2514/1.J061853
• Craig, S. A., Kocian, T. S., Moyes, A. J., Reed, H. L., Saric, W. S., Schneider, S. P., & Edelman, J. B. (2019). Hypersonic Crossflow Instability. Journal of Spacecraft and Rockets, 56(2), 432-446. doi:10.2514/1.a34289
  More info

  Under the auspices of NATO STO AVT-240: “Hypersonic Boundary-Layer Transition Prediction”, this paper describes the results of close collaborations among the authors toward the fundamental understa...
• Craig, S., Humber, R., Hofferth, J., & Saric, W. (2019). Nonlinear behaviour of the Mack mode in a hypersonic boundary layer. Journal of Fluid Mechanics, 872, 74-99. doi:10.1017/jfm.2019.359
• Kocian, T. S., Moyes, A. J., Reed, H. L., Craig, S. A., Saric, W. S., Schneider, S. P., & Edelman, J. B. (2018). Hypersonic Crossflow Instability. Journal of Spacecraft and Rockets. doi:10.2514/1.A34289
• Craig, S. A., & Saric, W. S. (2016). Crossflow instability in a hypersonic boundary layer. Journal of Fluid Mechanics, 808, 224--244. doi:10.1017/jfm.2016.643
• Craig, S. A., Prestridge, K., & Mula, S. M. (2016). Dynamics of Richtmyer-Meshkov (RM) mixing with reshock. Bulletin of the American Physical Society.
• Craig, S. A., & Saric, W. S. (2015). Crossflow Instability on a Yawed Cone at Mach 6. Procedia IUTAM. doi:10.1016/j.piutam.2015.03.019
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  Abstract Boundary-layer measurements were performed in a Mach 6, low-disturbance wind tunnel on a 7∘ cone at 5.6∘ angle of incidence such that the model was primarily subject to crossflow instability. Constant-temperature hot-wire anemometry was used to measure the streamwise mass flux at a series of planes normal to the cone axis. A dominant stationary wave is observed to achieve nonlinear saturation at approximately 23% with maximum rms fluctuations of approximately 8%. Additionally, traveling crossflow waves were observed in a broad frequency band centered at f = 40 kHz and secondary instabilities were observed in a broad band centered at f = 100 kHz. Measurements show excellent agreement with previously published computational results and are qualitatively similar to studies performed in subsonic flows. Transition to turbulence was not observed to occur under these conditions.
• Craig, S. A., Prestridge, K., Wilson, B., & Mejia-Alvarez, R. (2015). Richtmyer-Meshkov mixing: experiments on the effect of initial conditions. Bulletin of the American Physical Society.
• Craig, S. A., & Saric, W. S. (2014). Experimental study of crossflow instability on a Mach 6 yawed cone. Bulletin of the American Physical Society.
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  The crossflow instability is studied in the boundary layer on a yawed, 7◦ cone at 5.6◦ angle of incidence. Experiments are conducted in the Mach 6 Quiet Tunnel at Texas A&M University using constant temperature hot-wire anemometry at Re′ = 10× 10 m−1 with an adiabatic wall. Two-dimensional contours of mass flux are measured at a series of axial locations along the cone. Stationary crossflow waves are observed to dominate the flow field and reach saturation. Evidence of traveling waves are also observed to be increasingly confined to the regions between stationary vortices. Secondary instability is observed to arise along the leeward edges of the vortices and exhibits slow growth and saturation-like behavior. Transition was not observed on the model.
• Craig, S. A., Saric, W. S., Hofferth, J. W., McClure, P. D., Vadyak, J., & Humble, R. A. (2013). Spatiotemporal structure of a millimetric annular dielectric barrier discharge plasma actuator. Physics of Fluids. doi:10.1063/1.4774334
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  The spatiotemporal structure of a millimetric annular dielectric barrier discharge plasma actuator is investigated using a photomultiplier tube, a high-sensitivity camera, particle image velocimetry, and electrohydrodynamics simulations. Plasma actuators have typically demonstrated their utility in flow separation control, but on a millimetric scale they have also shown to be promising in the control of crossflow instabilities in crossflow-dominated laminar-turbulent boundary-layer transition. In view of the subtleties associated with creating an initial disturbance to excite subcritical wavelengths, it is desirable to characterize the local plasma discharge structure, body force organization, and induced velocity field in detail. The results show that, similar to their linear centimetric counterpart, the plasma discharge has a highly dynamic and somewhat organized spatiotemporal structure. Under quiescent flow conditions, the actuator induces a velocity field that consists of two counter-rotating vortices, accompanied by a wall-normal synthetic jet region, which in three-dimensions describes a toroidal vortex around the aperture's periphery. The surprising result, however, is that these vortices rotate in the opposite direction to vortices generated by similar centimetric annular designs. Three-dimensional electrohydrodynamics simulations correctly reproduce this behavior. Because the body force organization may be qualitatively perceived as being the axisymmetric counterpart of the more classical linear actuator, this flow reversal is thought to be due to the actuator scale. When an array of millimetric actuators is considered in close proximity, an interaction takes place between the vortices created from each actuator and those of neighboring actuators, resulting in a significant reduction in vortex size compared with the single aperture case, accompanied by an increase in the maximum induced flow velocity magnitude.
• Craig, S. A., Saric, W. S., Hofferth, J. W., & Humble, R. A. (2011). Flow-field characterization of DBD plasma actuators as discrete roughness elements for laminar flow control. Bulletin of the American Physical Society.

Proceedings Publications

• Craig, S. A., Flood, J. T., Hader, C., & Fasel, H. F. (2023). Experimental measurements and numerical investigations of boundary-layer instabilities on a Mach 5 hollow cylinder. In AIAA SciTech 2023.
• Flood, J. T., Craig, S. A., Little, J., Fasel, H. F., Hader, C., Jouannais, L., & Threadgill, J. A. (2022). Fin-induced Shock Boundary Layer Interactions on a Flat Plate and Hollow Cylinder at Mach 5. In AIAA SciTech 2022.
• Little, J. C., Craig, S., Flood, J., Hader, C., Jouannais, L., Threadgill, J. A., Threadgill, J. A., Jouannais, L., Hader, C., Flood, J., Craig, S., & 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.
• Bearden, K. P., Taubert, L., Craig, S. A., & Padilla, V. (2021). Calibration of a Mach 5 Ludwieg tube at the University of Arizona. In AIAA Aviation 2021.
• Flood, J. T., Threadgill, J. A., Singh, A., Little, J. C., Hader, C., Fasel, H. F., & Craig, S. A. (2021). Development of Plasma-based Controlled Disturbances for the Study of Boundary Layer Transition and Shock Boundary Layer Interaction. In AIAA AVIATION 2021 FORUM.
• Maldonado, J. C., Craig, S. A., Little, J., Wernz, S., & Threadgill, J. A. (2021). Flow Structure and Heat Transfer Characterization of a Blunt-Fin-Induced Shock-Wave/Laminar Boundary-Layer Interaction. In AIAA SciTech 2021.
  More info

  Revised version with modified coding in appendices approved by Graduate College 16-July-2021; revised PDF dissertation file added to UA Campus Repository 22-July-2021.
• Flood, J., Taubert, L., & Craig, S. (2020, January). First and Mack-mode instabilities in a flat-plate boundary layer at Mach 4. In AIAA SciTech 2020.
• Flood, J., Taubert, L., & Craig, S. (2020, January). Flow quality mapping of the Mach 4 Quiet Ludwieg Tube. In AIAA SciTech 2020.
• Taubert, L., Craig, S. A., & Flood, J. T. (2020). Correction: Flow quality mapping of the Mach 4 Quiet Ludwieg Tube. In AIAA SciTech 2020.
• Craig, S. A., Taubert, L., & Flood, J. T. (2019). Initial Flow Quality of the Mach 4 Quiet Ludwieg Tube. In AIAA Aviation 2019.
• Flood, J., Taubert, L., & Craig, S. (2019, June). Initial flow quality of the Mach 4 Quiet Ludwieg Tube. In AIAA Aviation 2019.
• Craig, S. A., Edelman, J. B., Schneider, S. P., Saric, W. S., Reed, H. L., Moyes, A., & Kocian, T. S. (2018). Hypersonic Crossflow Instability. In AIAA SciTech 2018.
  More info

  Under the auspices of NATO STO AVT-240: “Hypersonic Boundary-Layer Transition Prediction”, this paper describes the results of close collaborations among the authors toward the fundamental understa...
• Craig, S. A., & Saric, W. S. (2015). Experimental study of crossflow instability on a Mach 6 yawed cone. In AIAA Aviation 2015.
  More info

  The crossflow instability is studied in the boundary layer on a yawed, 7◦ cone at 5.6◦ angle of incidence. Experiments are conducted in the Mach 6 Quiet Tunnel at Texas A&M University using constant temperature hot-wire anemometry at Re′ = 10× 10 m−1 with an adiabatic wall. Two-dimensional contours of mass flux are measured at a series of axial locations along the cone. Stationary crossflow waves are observed to dominate the flow field and reach saturation. Evidence of traveling waves are also observed to be increasingly confined to the regions between stationary vortices. Secondary instability is observed to arise along the leeward edges of the vortices and exhibits slow growth and saturation-like behavior. Transition was not observed on the model.
• Craig, S. A., Saric, W. S., & Humble, R. A. (2011). Characterization of the Flowfield Structure of an Annular Dielectric Barrier Discharge Plasma Actuator. In 41st AIAA Fluid Dynamics Conference.
  More info

  The flowfield structure about annular dielectric barrier discharge plasma actuators is studied under quiescent flow conditions using particle image velocimetry. These actuators are currently under investigation for use as spanwise-periodic discrete roughness elements for laminar flow control on swept wings in both the wind-tunnel and flight. Aperture diameters considered vary from 3mm to 7 mm. Additionally, an arrayed actuator of five 3 mm apertures is considered. A complex flowfield is found to be generated, which consists of two counter-rotating vortices accompanied by a wall-normal jet region. The flowfield structure is shown to be sensitive to aperture size and applied voltage. For the arrayed actuator, the vortices contract dramatically due to the interaction of adjacent vortices from neighboring apertures. This work is the first step towards understanding the physical mechanism(s) of plasma actuators as discrete roughness elements for laminar flow control on swept wings.

Presentations

• Craig, S. (2017, Apr 17). High-speed stability and transition experiments at the University of Arizona. Invited Seminar. New Mexico State University.
• Craig, S. (2017, Feb 17). Boundary-layer stability and transition experiments at the University of Arizona. Invited Seminar. Purdue University.
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  Invited talk given to Purdue faculty and graduate students
• Craig, S. (2017, Mar 17). High-speed stability and transition experiments at the University of Arizona. Invited Seminar. NASA Langley Research Center.
• Mula, S., Craig, S., & Prestridge, K. (2016, 11). Dynamics of Richtmyer-Meshkov (RM) mixing with reshock. APS Division of Fluid Dynamics 2016. Portland, OR: American Physical Society.

Poster Presentations

• Tronstad, L., Threadgill, J. A., Little, J. C., & Craig, S. A. (2023). Heat Flux Measurements and Transition Prediction for the Construction of Surrogate Aerodynamic Databases. UCAH Spring Forum.