About

Dr. Christoph Brehm is an Associate Professor in the Department of Aerospace Engineering at the University of Maryland, Alfred Gessow Rotorcraft Center. He joined the university in 2021 after serving as an Assistant Professor at the University of Kentucky from 2016 to 2020. Prior to his academic appointments, he worked as a Senior Research Scientist at NASA Ames Research Center within the Science Technology Corporation's Advanced Supercomputing Division from 2012 to 2016. His research focuses on developing fundamental numerical methods for large-scale flow problems, including multi-physics effects, and on understanding the relevant physics of these phenomena. His recent work involves simulating and analyzing transitional and turbulent flows across low and high-speed regimes, with applications in laminar-turbulent transition, turbulence, relaminarization, aeroacoustics, fluid-structure interaction, and fluid-ablation interaction. Dr. Brehm has authored over 60 peer-reviewed journal and conference publications and has received multiple awards, including the 2022 NSF CAREER Award and the 2019 Office of Naval Research Young Investigator Award. His research is supported by various agencies such as NSF, NASA, ONR, AFOSR, and industry partners, in collaboration with several U.S. and international research institutions. He is actively involved in professional activities, including membership in NATO STO groups on hypersonic boundary-layer transition prediction and hypersonic turbulence, and serves as a co-organizer of the Large-Eddy Simulation (LES) AIAA Workshop 2022 and co-chair of the 2022 International Conference on Computational Fluid Dynamics. His work primarily advances the understanding of unsteady fluid dynamics, hypersonics, and aeroacoustics through the development of numerical methods and simulation tools.

Research topics

• Mechanics
• Mathematics
• Mathematical analysis
• Physics
• Classical mechanics
• Computer Science
• Geometry
• Materials science
• Computational science

Selected publications

• Leading-Edge Treatments for Wall-Modeled Large-Eddy Simulation of an Airfoil

  AIAA Journal · 2026-01-04

  article

  Wall-modeled large-eddy simulations (WMLES) of the Aerospatiale A-airfoil flow at Reynolds number of [Formula: see text], angle of attack of 13.3 deg, and Mach number of 0.15 are used as a test bed for exploring how to handle the thin laminar boundary layer and how it transitions to turbulence in a WMLES context. It is shown that application of the wall model everywhere with an unsuitable exchange location can lead to excessive boundary-layer growth and up to 10% underprediction of the lift coefficient. Several numerical approaches are examined to handle the laminar region of the airfoil flow within the WMLES framework. A transition sensor is implemented to locally detect where the boundary layer is laminar or turbulent and then used to dynamically activating or deactivating the wall model. The sensitivity of the predictions to the mesh resolution and the exchange location is explored.

  PublisherDOI

• Correction: Exploration of Phononic Subsurfaces for Hypersonic Boundary Layer Disturbance Reduction

  2025-07-29

  articleSenior author
  PublisherDOI

• Linear Analysis of Boundary-Layer Instabilities on a Finned Cone at Mach 6

  AIAA Journal · 2025-04-01

  articleSenior author

  Boundary-layer instabilities for a finned cone at [Formula: see text], [Formula: see text], and zero incidence angle are examined using linear stability methods of varying fidelity and maturity. The geometry and laminar flow conditions correspond to experiments conducted at the Boeing Air Force Mach 6 Quiet Tunnel at Purdue University. Where possible, a common baseflow is utilized among the stability computations, and comparisons are made along the acreage of the cone where transition is first observed in the experiment. Stability results utilizing linear stability theory, planar parabolized stability equations, one-way Navier–Stokes, forced direct numerical simulation, and adaptive mesh refinement wavepacket tracking are presented. A dominant three-dimensional vortex instability occurring at [Formula: see text] is identified and correlates well with experimental measurements of transition onset. With the exception of linear stability theory, all of the higher-fidelity linear methods considered in this work were consistent in predicting the initial growth and general structure of the vortex instability as it evolved downstream. Some of the challenges, opportunities, and development needs of the stability methods considered are discussed.

  PublisherDOI

• On the stability characteristics of a hypersonic boundary-layer flow over parametrised sinusoidal surface roughness

  Journal of Fluid Mechanics · 2025-04-10 · 5 citations

  articleOpen accessSenior author

  The stability characteristics of a Mach $5.35$ boundary-layer flow over a flat plate with parametrised two-dimensional sinusoidal surface roughness are investigated. The investigation involves varying the roughness height from $10\,\%$ to $44\,\%$ of the boundary-layer thickness and exploring wavelengths ranging between $0.44$ and $3.56$ times the dominant second-mode wavelength in the region. The introduction of surface roughness leads to notable variations in the mean flow, resulting in separation behind the roughness elements and the propagation of local compression and expansion waves into the free stream. Stability investigations involved the utilisation of wave packet tracking in a linear disturbance simulation (LDS) framework and linear stability theory. The findings revealed significant effects on Mack modes including a reduction in frequency corresponding to maximum amplification with increased roughness height. Proper scaling of the dominant wavelength facilitates a collapse of the growth rate data. In contrast to the commonly reported stabilisation effects for roughness wavelengths significantly larger than the instability mode’s wavelength, the findings primarily revealed destabilisation compared with the smooth-wall case, except for cases with very small roughness wavelengths and large amplitudes approaching the threshold of being classified as porous media. The LDS findings depicted lobed wall pressure amplitude plots, indicating potential undiscovered instability mechanisms or differences compared with the smooth wall. A detailed stability analysis elucidates these LDS findings, establishing a connection between the lobed amplitude structures and substantial changes in local stability characteristics, along with the emergence of Mack’s first, second and third modes.

  PublisherDOI

• Wall-Modeled Large Eddy Simulation Using the Immersed Boundary Method of the HVAB Rotor

  2025-01-03 · 1 citations

  article

  Immersed boundary methods have historically been used for low-Reynolds-number flows or scenarios where near-wall viscous effects are less significant. However, recent research has shown that, when combined with wall-modeled large eddy simulations, these methods offer a robust solution for high-Reynolds-number flows. This work presents a WMLES-IBM solver framework within the Cartesian Higher-Order Adaptive Multi-Physics Solver for GPUs (CHAMPS+) to leverage the computational power of GPU architectures to provide higher fidelity solutions for rotorcraft problems. The CHAMPS+ WMLES-IBM solver is validated on the NASA Hover Validation and Acoustic Baseline (HVAB) rotor test case for a range of collective pitch angles, showing good agreement on overall rotor performance, blade pressure distributions and blade loadings against the US Air Force National Full-Scale Aerodynamics Complex (NFAC) test campaign. CHAMPS+ is capable of producing high fidelity solutions with minimal GPU resources at time scales that are useful for design level analysis.

  PublisherDOI

• Effects of Injection Gas Temperature on Stability of High-Enthalpy Boundary Layer Flows With Transpiration Cooling

  2025-01-03

  articleSenior author

  The management of intense thermal loads encountered by hypersonic vehicles operating in the atmosphere can be effectively alleviated by utilizing transpiration cooling, which involves the injection of cold fluids at the vehicle's surface. However, this injection process can substantially impact flow stability and potentially induce a premature transition to turbulence. The primary objective of this study is to comprehensively understand the mechanisms responsible for destabilizing flow during transpiration cooling application. To assess the influence of injection gas properties on the stability of high-enthalpy boundary layer flows, air and CO$_2$ injections are being considered. Both fluids are introduced at the same mass flux, resulting in a comparable reduction in heat flux. A reduction in the boundary layer thickness was noted due to the decrease in thermal-diffusivity with CO$_2$ injection compared to air. The injection of air caused the neutral curve to shift further upstream compared to the no-blowing case. Additionally, the frequency leading to the maximum amplification shifted to lower values due to increased Reynolds number based on the boundary layer thickness. The increased destabilization observed with CO$_2$ injection can be attributed to reduced dissipation compared to air injection.

  PublisherDOI

• Extubation of patients with COVID-19 acute respiratory failure during extracorporeal membrane oxygenation support is associated with improved survival

  Exploration of Cardiology · 2025-02-05

  articleOpen access

  Aim: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), or COVID-19, infection resulting in acute respiratory distress syndrome (ARDS) requiring veno-venous or veno-arterial extracorporeal membrane oxygenation (VV or VA-ECMO) support is a life-threatening disease process that requires prolonged intubation and has a high risk of mortality. Methods: In this retrospective, observational, single-center cohort study, we attempt to better understand the role of extubation in the course of treatment by dichotomizing groups into those extubated early while remaining on ECMO treatment (group A), compared to patients who remained intubated for the entirety of their ECMO treatment (group B). Results: The data indicate that early extubation of patients with COVID-19-associated ARDS requiring ECMO support leads to improved survival rates for group A (93%) compared to prolonged intubation (group B) throughout the course of ECMO therapy (64%) (p = 0.13). Additionally, patients extubated earlier (19 days vs. 59 days; p = 0.012) required significantly fewer vasoactive drugs (norepinephrine dosing: 0.03 mcg/kg/min vs. 0.093 mcg/kg/min; p = 0.04), and were less likely to require a tracheostomy (0 vs. 4, p = 0.026). Conclusions: Although the utility of ECMO in severe ARDS patients remains a contentious topic, early extubation seems to increase survival rates and overall patient outcomes in patients with COVID-19-associated ARDS requiring ECMO support.

  PublisherOA PDFDOI

• Wall Temperature Effects on High Enthalpy Hypersonic Boundary Layer Stability

  2025-01-01

  articleSenior author

  The design of practical high-speed vehicles is constrained by the extreme thermo-mechanical surface loads which occur when traveling at high Mach number. This is further complicated by the dramatic increase in surface heat flux which accompanied with laminar-turbulent transition. Hence, understanding the stability characteristics of hypersonic boundary layers is crucial for advancing high-speed flight technology. At high-enthalpy conditions observed during high Mach number flight, real gas effects such as molecular dissociation significantly alter flow characteristics, also strongly influencing the boundary layer stability characteristics. This study investigates the flat plate boundary layer instabilities under high-enthalpy conditions, with a fixed freestream temperature of 2500K and wall temperatures of 300K, 700K, and 1100K. First, the baseflow was computed considering a 5-species air and Park’s two-temperature model. Next the evolution of the instability waves was simulated by employing a harmonic balance approach accounting for non-parallel and high enthalpy. Using Fourier analysis, the dominant instability modes were identified, revealing their spatial growth and frequency characteristics. The stability results show that the change in wall temperature strongly affects the stability characteristics and will increase or decrease the disturbance flow growth depending on the instability mechanism, e.g. first versus second mode waves. Furthermore, the appearance of the supersonic mode can be observed for large wall temperature to edge temperature ratios. In summary, this research provides insight into the mechanisms driving hypersonic boundary layer instability in chemically reacting flows, with important implications on predictive modeling of hypersonic flows and vehicle design.

  PublisherDOI

• Transpiration cooling in hypersonic flow and mutual effect on turbulent transition and cooling performance

  Physics of Fluids · 2025-02-01 · 9 citations

  articleOpen access

  This work presents recent advancements in the study of film cooling in hypersonic flows, considering experimental and numerical investigations, with the aim to characterize the wall-cooling performance in different coolant injection and baseflow conditions in a Mach number range 2–7.7. The study explores the mutual interaction between the injected coolant film and the boundary-layer flow, with emphasis on the effects of wall blowing on the boundary-layer characteristics, stability, and transition to turbulence, as well as the effect of transition on wall-cooling performance. Considered flow configurations include cases of effusion cooling in both wall-normal or slightly inclined and wall-parallel blowing, different types of coolant, cases of favorable pressure gradient compared to zero pressure gradient, as well as transpiration cooling cases at different blowing ratios and surface geometries. For the transpiration cooling case, experiments in different hypersonic wind tunnel facilities are presented for flat plate and cone geometries, with coolant injected through C/C porous samples, whereas numerical simulations of modeled porous injection are presented for a flat plate and a blunt cone, showing results for the boundary-layer receptivity with coolant injection and the associated effects on transition and cooling performance. A summary of the main findings is provided along with a critical analysis based on a comparative study to evaluate the effect of each configuration, injection strategy, and key parameters on the boundary-layer flow and the feedback on wall-cooling performance. Conclusions are drawn about potential directions of study for the further development and optimization of the film cooling technique for future hypersonic vehicles.

  PublisherDOI

• A Multi-Material Approach to Damage Modelling in High-Speed Droplet Impacts

  2025-01-03 · 1 citations

  articleSenior author

  High-speed impacts on aerodynamic surface is a multi-material phenomenon involving gases, liquids, and solids. The effects of such impacts results in coupled aerodynamic, thermal, and mechanical effects. The main objective of the paper is to describe the implementation and validation of a diffuse interface multi-material method suitable for damage modeling in high-speed impacts. Physical and numerical methods implemented in a GPU accelerated Cartesian adaptive mesh refinement solver (CHAMPS+) are described. Two approximate Riemann solvers: two-wave path-conservative HLL and five-wave HLLD solvers are compared. Riemann problems without solid material and Water-Air fluid, Elastic solid with Aluminum Copper and Elastoplastic Solid-Gas are used for validation.

  PublisherDOI

Frequent coauthors

• Cetin C. Kiris

  Volcano Corporation (United States)

  32 shared

• Hermann F. Fasel

  University of Arizona

  31 shared

• Michael F. Barad

  Ames Research Center

  28 shared

• Ali Ghodsizad

  University of Miami

  26 shared

• Joel A. McQuaid

  University of Maryland, Baltimore

  23 shared

• Behzad Soleimani

  Penn State Milton S. Hershey Medical Center

  22 shared

• Aly El‐Banayosy

  University of Oklahoma Health Sciences Center

  20 shared

• Sparsh Ganju

  University of Maryland, Baltimore

  17 shared

Awards & honors

• 2022 National Science Foundation CAREER Award
• 2019 Outstanding Researcher Award (UK)
• 2019 Office of Naval Research Young Investigator Award (ONR)
• 2014 Best Young Researcher Presentation Award, 3rd AIAA Work…
• 2008 Biology, Mathematics and Physics Initiative (BMPI)-BIO5…