James Threadgill

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Scholarly Contributions

Books

• Threadgill, J. A. (2017).

  Unsteadiness of shock wave boundary layer interactions across multiple interaction configurations and strengths

  . doi:10.25560/48475

Journals/Publications

• Threadgill, J. A., & Little, J. (2023).

  Correction to: Volumetric study of a turbulent boundary layer and swept impinging oblique SBLI at Mach 2.3

  . Experiments in Fluids. doi:10.1007/s00348-023-03689-6
• Threadgill, J. A., & Little, J. C. (2022). Volumetric study of a turbulent boundary layer and swept impinging oblique SBLI at Mach 2.3. Experiments in Fluids, 63(9), 20. doi:10.1007/s00348-022-03433-6
• Little, J. C., Threadgill, J. A., & Wernz, S. H. (2021).

  Transitional Shock Boundary Layer Interactions on a Compression Ramp at Mach 4

  . AIAA Journal, 59(12), 4824-4841. doi:10.2514/1.j059981
  More info

  Strong laminar/transitional shock boundary layer interactions (SBLIs) have been investigated in a Mach 4 vacuum-driven wind tunnel with supporting computational fluid dynamics analysis. Such flows are extremely susceptible to large-scale separation, unsteadiness, and high surface heat flux, which can limit control authority on high-speed vehicles. The research community has heavily focused on turbulent interactions, leaving little understanding of how laminar/transitional cases behave with varying external parameters. Four compression ramp angles of 15, 18, 22, and 28° have been tested on a flat plate (unit Reynolds number ) with a range of external length scales (flat plate Reynolds number varies between and at the ramp corner). Laminar separation was observed at boundary-layer thickness Reynolds number between 2700 and 4300, with the centerline length of separation scaling mildly with Reynolds number, increasing proportionally with . Transitional reattachment is observed for strong SBLIs at higher values of . Analysis of high-speed schlieren images shows that the separation shock exhibits low-frequency unsteadiness at a Strouhal number near , consistent with turbulent SBLIs. Detailed phase analysis of schlieren data shows no evidence of upstream influence. Instead, motion of the shear layer and reattachment shock precedes motion of the separation shock foot, suggesting a downstream unsteadiness mechanism. In addition, extensive analysis of subtle features within the interaction identified a slow-moving density disturbance within the bubble that convects toward the shock foot and directly leads separation shock motion. Negligible coherence was observed between low-frequency separation shock motion and acoustic content within the separation bubble.
• Bruce, P. J., & Threadgill, J. A. (2020).

  Unsteady Flow Features Across Different Shock/Boundary-Layer Interaction Configurations

  . AIAA Journal, 58(7), 3063-3075. doi:10.2514/1.j058918
• Threadgill, J. A., & Little, J. (2020).

  An inviscid analysis of swept oblique shock reflections

  . Journal of Fluid Mechancis. doi:10.1017/jfm.2020.117

Proceedings Publications

• Fasel, H. F., Hader, C., Little, J. C., Singh, A., & Threadgill, J. A. (2023).

  Schlieren Visualization of Controlled Disturbances in Mach 5 Flow Over a Hollow Cylinder Flare

  . In AIAA SciTech 2023.
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  The formation and evolution of a broadband point source disturbance in a Mach 4.82 laminar flow is characterized over a 15° hollow cylinder flare model. A forcing strategy, commonly known as Localized Arc Filament Plasma Actuators (LAFPAs), which functions via thermal energy deposition is employed. The LAFPA serves as a point source and its extremely short duration (≈ 300𝑛𝑠) is used to create a broadband disturbance in the flow. By using high-speed schlieren imaging phase locked to the LAFPA discharge, the evolution of the generated wave packet is characterized at various downstream locations over the model. Spectral and modal analysis of the pixel intensity of schlieren images obtained without the use of LAFPA (baseline) confirms the presence of first mode waves occurring naturally in the flow. These waves compare well with oblique first mode waves predicted by LST. Analysis of schlieren images during forcing is used to visualize the interaction of the disturbance with the base flow. Novel experimental information about the off-body density disturbance reveals the location and spread of the disturbance as it convects in the laminar boundary layer and lifts off into the separated shear layer. The disturbances introduced by the LAFPA successfully increases the amplitude of the first mode waves compared to the baseline case.
• Little, J. C., Roskelley Garcia, A., Singh, A., & Threadgill, J. A. (2023).

  Boundary Layer Separation on a Hollow-Cylinder/Flare at Mach 5

  . In AIAA SciTech 2023.
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  A $\theta=15^\circ$ hollow-cylinder/flare model is assessed in Mach~5 flow at ${1.2\times10^6}
• Lum, J. S., Goldberg, B. M., Busby, E., Stobbe, D. M., Threadgill, J. A., Singh, A., Little, J., & Rousso, A. (2023).

  In-Situ Laser-Based Ultrasonic Measurement of Material Cooling from Supersonic and Hypersonic Flow

  . In AIAA Aviation 2023.
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  In this study, we demonstrate using laser-based ultrasonics as an in-situ measurement technique to characterize temperature changes of a heated aluminum coupon in The University of Arizona Indraft Supersonic Wind Tunnel at Mach 2.3 and Mach 5. Changes in ultrasound time-of-arrivals were measured for aluminum at room temperature versus at an elevated 120 °C while exposed to both Mach 5 and Mach 2.3 flow. These measured differences agree well with expected material thickness and speed of sound changes. Laser-based ultrasound measurements in the experimental configuration using a Sagnac interferometer were found to be less sensitive for accurately monitoring small temperature changes, such as the cooling of the aluminum coupon from 120 °C to ~100 °C by tunnel flow. Additional laser-based ultrasound measurements using a multi-channel random-quadrature interferometer suggests greater sensitivity to small temperature changes may be achievable and could improve in-situ monitoring of material cooling during wind tunnel flow. Results from this study help encourage future applications of laser-based ultrasound as a method for in-situ material characterization for hypersonic research.
• Padmanabhan, S., Jouannais, L., Threadgill, J. A., & Little, J. (2023).

  Laminar/Transitional Fin-induced Shock Wave Boundary-Layer Interactions at Mach 5

  . In AIAA SciTech 2023.
  More info

  Fin-induced Shock Boundary Layer Interactions (SBLIs) are investigated on a hollow cylinder at Mach 5 across a range of Reynolds numbers $1.27\times 10^6 < {Re}_{ x_{f}} < 4.90\times 10^6$. Unsteady pressure measurements demonstrate that the incoming boundary layer contains transitional features for all cases. Infrared thermography (IRT) is used to measure surface heat transfer characterizing the global structure of the SBLI. IRT results show transitional behavior within SBLI, with a downstream shift in separation location and the development of secondary separation for the highest Reynolds number case (${Re}_{x_{f}} = 4.90\times 10^6$). An elevated region of surface heat transfer is observed near reattachment for all cases but is segmented at low Reynolds numbers. RMS pressure levels and spectra within the SBLI increase with an increase in Reynolds number. The highest Reynolds number case (${Re}_{x_{f}} = 4.90\times 10^6$) demonstrates low frequency unsteadiness near reattachment and significantly greater unsteadiness throughout the SBLI.
• 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., 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.
• Padmanabhan, S., Threadgill, J. A., & Little, J. C. (2022, January). Flow Similarity in Swept Shock/Boundary Layer Interactions. In AIAA Scitech 2022 Forum, 18.
• Castro Maldonado, J., Craig, S. A., Little, J. C., Threadgill, J. A., & Wernz, S. H. (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.
• Gross, A., Little, J. C., Threadgill, J. A., & Weiss, J. (2021).

  Low-Frequency Unsteadiness in Pressure-Induced Separation Bubbles

  . In AIAA SciTech 2021.
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  Existing results on low-frequency unsteadiness in pressure-induced separation bubbles at different speed regimes and states of the incoming boundary layer are reviewed. Specifically, results are presented for low- and high-Mach number separation bubbles where the incoming boundary layer is either laminar/transitional or turbulent. The review indicates that there are strong similarities in low-frequency behavior between the different flow cases. Nevertheless, the available database is not sufficient to firmly establish a common phenomenology.
• Padmanabhan, S., Maldonado, J. C., Threadgill, J. A., & Little, J. (2021).

  Experimental Study of Swept Impinging Oblique Shock/Boundary-Layer Interactions

  . In AIAA SciTech 2019, 59, 140-149.
• Singh, A., Threadgill, J. A., Flood, J. T., Craig, S. A., Little, J., 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.
  More info

  Plasma actuators have been developed and studied for the use of controlling hypersonic boundary layer physics. The goal is to manipulate the incoming boundary layer state to control the behavior of shock boundary layer interactions (SBLIs). The surface based plasma actuators, referred to as localized arc filament plasma actuators (LAFPAs), deposit energy into the flow and excite otherwise less amplified boundary layer instabilities. This paper describes the development process of the actuators and an initial investigation into their effect on a SBLI. A Mach 5 nozzle was developed for the in-draft wind tunnel at University of Arizona was developed to act as a test bed for the actuators before testing them in larger Reynolds number facilities. A characterization of the flow was performed and the nozzle shows repeatable Mach 5 flow that is uniform across the tunnel span. Electrical data acquired in a vacuum chamber helps characterize plasma behavior. Whether an arc or a glow discharge is heavily dependent on the static pressure. Quiescent tests show there is a crossover regime where the the plasma transitions from an arc discharge to a glow discharge as static pressure decreases. Pressure measurements on the tunnel wall and schlieren were performed to identify the forced boundary layer structures and the instabilities present. Wavepackets associated with the second mode instability are found in good agreement with linear stability analysis. A methodology to visualize these forced structures with schlieren is developed and preliminary results look promising.
• Castro Maldonado, J., Little, J. C., Padmanabhan, S., & Threadgill, J. A. (2020).

  Root Influence on the Unsteady Characteristics of Swept Impinging Oblique SBLIs

  . In AIAA SciTech 2020.
• Castro Maldonado, J., Little, J. C., Padmanabhan, S., & Threadgill, J. A. (2019).

  Experimental Study of Swept Impinging Oblique Shock Boundary Layer Interaction

  . In AIAA SciTech 2019.
• Maldonado, J. C., Padmanabhan, S., Threadgill, J. A., & Little, J. (2019).

  Root Influence on Swept Impinging Oblique Shock Boundary Layer Interactions

  . In AIAA SciTech 2020.
• Padmanabhan, S., Maldonado, J. C., Threadgill, J. A., & Little, J. (2019).

  Mean and Unsteady Characteristics of Swept SBLIs

  . In APS DFD 2019.
• Threadgill, J. A., & Little, J. (2019).

  Phase Analysis of Disturbances within Transitional Shock Boundary Layer Interactions.

  . In APS DFD 2019.
• Threadgill, J. A., Little, J., & Wernz, S. (2019).

  Transitional Shock Wave Boundary Layer Interactions on a Compression Ramp at Mach 4

  . In AIAA SciTech 2020.
• Doehrmann, A., Padmanabhan, S., Threadgill, J. A., & Little, J. (2018).

  Effect of Sweep on the Mean and Unsteady Structures of Impinging Shock/Boundary Layer Interactions

  . In AIAA SciTech 2018.
• Little, J. C., & Threadgill, J. A. (2018).

  Volumetric Study of a Turbulent Boundary Layer and Swept Impinging Oblique SBLI at Mach 2.3

  . In AIAA Aviation 2018.
• Little, J. C., Stab, I., Threadgill, J. A., & Wernz, S. H. (2018).

  Influence of Flat Plate Leading Edge Sweep and Boundary Layer State on Unswept Shock Boundary Layer Interaction

  . In AIAA SciTech 2018.
• Doehrmann, A., Little, J. C., Stab, I., & Threadgill, J. A. (2017).

  Three-Dimensional Flow Features of Swept Impinging Oblique Shock/Boundary-Layer Interactions

  . In AIAA SciTech 2017.
• Threadgill, J. A., & Bruce, P. J. (2017).

  Comparison of Unsteady Flow Similarities in Various Shock/Boundary-Layer Interaction Configurations

  . In AIAA SciTech 2017.
• Little, J., Threadgill, J. A., Stab, I., & Doehrmann, A. (2016).

  Swept Impinging Oblique Shock/Boundary-Layer Interactions

  . In APS DFD 2016.
• Stab, I., Threadgill, J. A., & Little, J. (2016).

  Influence of Mach Number and Incoming Boundary Layer on Shock Boundary Layer Interaction

  . In APS DFD 2016.
• Threadgill, J. A., & Bruce, P. J. (2016).

  Shock Wave Boundary Layer Interaction Unsteadiness: The Effects of Configuration and Strength

  . In AIAA SciTech 2016.
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  Unsteadiness associated with shock wave boundary layer interactions across a variety of environments is the focus of the experimental study reported herein, recorded via synchronized high-speed measurement of planar velocity fields and wall-pressures. Such unsteadiness has been witnessed to present at frequencies much lower than that found in the incoming boundary layer, and has been linked with a range of damaging local flow phenomena. Despite significant research, there remains considerable disagreement as to the core mechanisms involved. Recent work suggests upstream fluctuations are significant in lowstrength interactions, while downstream effects appear dominant in high-strength interactions. The situation for intermediate strength interaction, i.e. incipiently separated flow, is less clear and appears to display a mixture of these influences. In this study we analyze the interaction with two different configuration types, each with multiple cases varying interaction strength, from incipiently separated interactions to those featuring fully separated flow. 14◦ and 20◦ compression ramp interactions are observed in the Mach 2.0 facility, along with oblique shock reflection interactions induced by 7◦, 8◦, 9◦, and 10◦ shock generators. Resultant unsteadiness beneath the interaction is recorded with a series of fast-response wall-pressure transducers. The approach is unique in that these interactions have been tested in a single facility, with common inflow conditions, limiting other external influences. Scaling of the mean interaction structures by length and imposed interaction strength collapse well to recent models proposed in literature. Unsteady wall pressure spectra agree with similar trends observed in other facilities.
• Threadgill, J. A., & Bruce, P. J. (2015).

  Unsteadiness in Shock Wave Boundary Layer Interactions across Multiple Interaction Configurations

  . In AIAA SciTech 2015.
  More info

  The effects of interaction strength and configuration generality are the subject of an experimental investigation to assess the low frequency unsteadiness typically observed in Shock Wave Boundary Layer Interactions (SWBLIs). The core dominant mechanisms responsible remain disputed due to the lack of a broad approach for understanding what drives each mechanism across a range of interaction types. This paper forms the first part of an investigation to observe various interactions in a well characterized baseline environment. Experiments have been conducted in the Imperial College London supersonic wind tunnel where three configurations of SWBLI have been tested, each with a strength of interaction designed to result in incipient separation: a) 14◦ compression ramp interaction (Mach 2.0), b) 8◦ incident shock reflection interaction (Mach 2.0), and c) normal shock interaction (Mach 1.4). Analysis has been conducted using high-speed planar two-component particle image velocimetry and schlieren photography to characterize the baseline flow and inspect shock unsteadiness. Each configuration exhibits similar levels of incipient separation with probabilities of reversed flow between 12% and 26% in each frame. Significant energy content has been observed within the interactions at frequencies far lower than typically witnessed in a supersonic boundary layer, providing agreement with results in literature.
• Threadgill, J. A., & Bruce, P. J. (2014).

  Study of transonic shock wave/boundary layer interactions subject to unsteady forcing

  . In AIAA SciTech 2014.

Presentations

• Threadgill, J. (2023). Comparison on Hollow Cylinder/Flares (HCF). NATO STO AVT-346 - Fall Meeting. Dayton, OH.
• Threadgill, J. (2023). Recent Progress on UArizona Hollow Cylinder Flare. NATO STO AVT-346 - Spring Meeting. London, UK.
• Threadgill, J. A. (2023). An Overview of Experimental Investigations on Shock Boundary Layer Interactions and Transition. Seminar. ONERA, Meudon, France.
• Threadgill, J. A. (2023). Investigations of Complex Shock/Boundary Layer Interaction Topologies and Dynamics. Seminar. University of Arizona.

Poster Presentations

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