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Physics Modeling and Validation

Improvements in physical modeling and the validation of these methods are critical to advancing numerical simulation capabilities.

Boundary Layer Bleed Modeling
Vortex Generator Modeling
Large Eddy Simulation (LES)

Boundary Layer Bleed Modeling

Color diagram showing Mach number distribution around a sloped object in a wind tunnel. The flow, labeled M = 2.46, forms shock waves and expansion fans. Axes are labeled in inches; a color bar indicates Mach values from 0 to 2.5.
Oblique shock interaction with bleed model boundary condition.
NASA/John Slater

The modeling of porous bleed boundary conditions was improved by scaling sonic flow coefficient data for 90-degree bleed holes. The updated bleed model showed good agreement with experimental data and three-dimensional computational fluid dynamics (CFD) simulations.

Area of ExpertiseResearcher NameEmail
Bleed ModelingJohn Slaterjohn.w.slater@nasa.gov
Bleed ModelingChristine Pastor-Barsichristine.m.pastor@nasa.gov

Vortex Generator Modeling

Including small-scale geometric features, such as vortex generators, in numerical simulations can be tedious and computationally expensive. Replacing these physical elements with modeled source terms can significantly streamline preliminary design studies.

Mach number contours for gridded vortex generator (left) and modeled vortex generator (right).
NASA/Julianne Dudek
Area of Expertise Researcher NameEmail
Vortex Generator Modeling in Structured Reynold’s-Averaged Navier-Stokes SolversJulianne Dudekjdudek@nasa.gov

Large Eddy Simulation (LES)

Scale-resolving simulations are increasingly used to improve the understanding and prediction of complex flow physics.

LES of a Hot Subsonic Jet

One example of how LES can inform turbulence modeling is in the prediction of hot jets. In this study, the WRLES solution was validated using individual velocity (v) and temperature (T) data. LES was then employed to compute the turbulent heat flux correlation (vT), as simultaneous measurement of velocity and temperature at a single point is not practical.

The results revealed the limitations of the thermal gradient diffusion approximation commonly used in most RANS turbulence models.

Contour plot showing a jet spread horizontally from left to right, with color gradients from red (high values) to blue (low values). Axes are labeled x/Dj (horizontal) and r/Dj (vertical). A color bar indicates value levels, 0.012 to 0.
LES prediction of turbulent heat flux in a hot subsonic axisymmetric jet.
NASA/James DeBonis

Wall Resolved LES of a Backward Facing Step

Accurately predicting flow separation remains one of the most significant challenges in computational fluid dynamics. Separation can occur in inlets and diffusers, where it adversely affects propulsion system efficiency and operability. Reynolds-averaged Navier-Stokes (RANS) methods typically perform poorly in regions with separated flow. Scale-resolving simulation (SRS) approaches have demonstrated the ability to capture such phenomena, albeit at significantly higher computational cost.

The backward-facing step is a canonical case used to isolate the effects of separation and reattachment by removing the separation point. NASA’s Wave Resolving Large-Eddy Simulation (WRLES) code was applied to this configuration and produced flow separation predictions that outperformed those generated by RANS models.

Visualization of turbulent airflow over a flat surface, with swirling red, orange, yellow, and blue patterns indicating velocity magnitudes; a color bar and 3D axes are shown for reference.
Iso-contours of q-criterion colored by streamwise velocity depicting a turbulent separating flow over a backward facing step.
NASA/James DeBonis
  • DeBonis, J.R., “A Large-Eddy Simulation of Turbulent Flow Over a Backward Facing Step,” AIAA Paper 2022-0337, Jan. 2022.

Scale Resolving Simulations of the Taylor-Green Vortex Flow

The Taylor-Green vortex (TGV) is a canonical fluid dynamics problem developed to study vortex dynamics, transition to turbulence, turbulent decay, and energy dissipation. It captures several fundamental physical processes of turbulence within a simplified construct, making it an ideal case for evaluating turbulent flow simulation methodologies.

The problem consists of a cubic fluid domain with a smooth initial vorticity distribution. As the flow evolves, the vortices roll up, stretch, and interact—ultimately breaking down into turbulence. NASA’s Wave Resolving Large-Eddy Simulation (WRLES) high-order-accuracy solver was applied to this case to assess its capability to predict the underlying physical processes. The results demonstrated strong agreement with reference data, and the effects of solver order, grid resolution, and subgrid-scale modeling were systematically examined.

Animation of iso-contours of strain depicting the transition and decay of the Taylor-Green vortex.
NASA/James DeBonis
  • DeBonis, J.R., “Solutions of the Taylor-Green Vortex Problem Using High-Resolution Explicit Finite Difference Methods,” AIAA Paper 2013-0382, Jan. 2013.
Area of Expertise Researcher NameEmail
Large Eddy Simulations of Propulsion FlowsJames DeBonisjames.r.debonis@nasa.gov

WMLES of a Subsonic Jet

Wall-modeled large-eddy simulations (WMLES) avoid resolving the steep flow gradients within the inner boundary layer by modeling the wall shear stress and applying it as a boundary condition. This approach results in significant computational cost savings compared to wall-resolved large-eddy simulations.

Visualization of turbulent fluid flow from a nozzle, showing swirling patterns in shades of purple, green, and yellow. A color scale at the top left indicates velocity magnitude from 0 to 1.
Instantaneous plot of q-criterion in a Mach 0.5 jet exhaust, displaying vortical structures. Structures are colored by axial velocity, normalized by ideal jet velocity. The symmetry plane shows density gradient.
NASA/Brian Heberling
Area of ExpertiseResearcher NameEmail
Wall-Modeled Large Eddy SimulationsBrian Heberlingbrian.heberling@nasa.gov

LES of a Shock-Wave Boundary-Layer Interaction (SWBLI)

LES of a shock-wave boundary-layer interaction in a rectangular duct. The instantaneous solution on the far side displays isosurface of Q-criterion (Q = 0.5) colored by the mean streamwise velocity to show eddies in the turbulent boundary layer along the bottom wall, the impinging shock, and the reflected shock. The instantaneous solution in the near side displays contours of the mean streamwise velocity at the y = 1 mm plane showing streaks of the low- and high-momentum flow upstream of the SWBLI, secondary flow in the corner, and separation regions (colored by magenta).
NASA

Another example of complex flow physics under investigation is the influence of sidewall effects on an impinging shock-wave boundary-layer interaction. Statistics from this simulation, conducted using the FDL3DI solver, will be used to inform turbulence model development.

  • Vyas, M.A., Yoder, D.A., and Gaitonde, D.V., “Reynolds-stress Budgets in an Impinging Shock Wave/Boundary-layer Interaction,” AIAA Journal, 57(11):4698–4714, Nov. 2019.
  • Vyas, M.A., et al., “Sidewall Effects on Exact Reynolds-Stress Budgets in an Impinging Shock Wave/Boundary Layer Interaction,” NASA/TM-2019-220143, Mar. 2019. Also AIAA-2019-1890.
Area of ExpertiseResearcher NameEmail
SWBLI SimulationsManan Vyasmanan.vyas@nasa.gov

LES of a THX3 Single Cooling Hole Experiment

Comparison of mean temperature from LES and RANS of the THX Phase III single cooling hole experiment.

A comparison of experimental and simulated temperature fields, shown as heatmaps, at various x/D positions (3 to 15) for Exp Raman Data, FDL3DI, GFR, and FUN3D RSM models.
Comparison of mean temperature from LES and RANS of the THX Phase III single cooling hole experiment.
NASA/Michael Borghi
A grid of contour plots showing uT/(U_jet^2 ΔT) predictions from FDL3DI, GFR, and FUN3D RSM models at various x/D locations (3 to 15). Color scale ranges from -0.024 (blue) to 0.04 (red).
Comparison of axial component of turbulent heat flux from LES and RANS of the THX Phase III single cooling hole experiment.
NASA/Seth Spiegel

Another example is the FDL3DI and GFR simulations of the THX Phase III single cooling hole experiment described above. In this case, velocity and temperature predictions were again compared with experimental data. LES-derived values of turbulent heat flux (vT) were then used to assess turbulence model performance.

  • Spiegel, S.C., Borghi Jr., M.R., and Yoder, D.A., “Large Eddy Simulations of a Single-Injector Cooling Flow Using the High-Order Flux Reconstruction Method,” AIAA-2022-1813, Jan. 2022.
  • Borghi Jr., M.R., “Implicit Large-Eddy Simulation of Single-Injector Cooling Flow,” AIAA-2022-1814, Jan. 2022.
  • Borghi Jr., M.R., Spiegel, S.C., Yoder, D.A., Georgiadis, N.J., and Wernet, M.P., “Turbulent Simulations of Cooling Jets in Crossflow,” AIAA-2022-1815, Jan. 2022.
  • Yoder, D.A., “Assessment of Turbulence Models for a Single-Injector Cooling Flow,” AIAA-2022-1812, Jan. 2022.
Area of ExpertiseResearcher NameEmail
THX3 Single Cooling Hole SimulationsSeth Spiegelseth.c.spiegel@nasa.gov

LES of a Spacecraft Cabin Ventilation Fan

Colorful streamlines around a 3D object, visualizing fluid flow with varying speeds, indicated by a color bar labeled “RelativeMach” with values from 0.005 to 0.155. An XYZ axis is shown for reference in the top right corner.
Particle streamtraces of flow along the suction side of the Quiet Space Fan rotor blades from fifth-order LES using GFR. Streamtraces are colored by Mach number relative to the rotating reference frame.
NASA/Seth Spiegel
Animation of flow over the tip of the Quiet Space Fan rotor blades from fifth-order LES using GFR. Contours show radial velocity midway between the rotor blade tips and the stationary outer casing. The rotor blade tips are moving in the background behind the contours, with the fan inlet located at the bottom.
NASA/Seth Spiegel

This example of LES involves the Quiet Space Fan (QSF) prototype, a ventilation fan designed to reduce cabin noise in future crewed spacecraft and space stations. The QSF was used to test three significant new capabilities in the high-order GFR code: improved time-to-solution performance, fully unstructured mixed-element meshes, and a rotating reference frame for simulating turbomachinery.

Fourth- and fifth-order simulations revealed evidence of flow separation on the suction side of the rotor blades—features not previously detected in experiments or Reynolds-averaged Navier-Stokes (RANS) simulations. These insights could help improve the efficiency and noise reduction of future prototypes prior to deployment in space missions.

  • Spiegel, S.C., Yoder, D.A., DeBonis, J.R., Huynh, H.T., Heinlein, G.S., Borghi Jr., M.R., and Georgiadis, N.J., “New Capabilities and Improvements to the High-Order Glenn Flux Reconstruction Code,” AIAA-2025-0061, Jan. 2025. Also 2025 SciTech Forum presentation.
Area of ExpertiseResearcher NameEmail
Spacecraft Cabin Ventilation Fan SimulationsSeth Spiegelseth.c.spiegel@nasa.gov

Scale Resolving Simulations of Compressible Mixing Layers

Inlet and nozzle researchers have investigated compressible mixing layers using experimental data from the University of Illinois Urbana-Champaign (UIUC) group, as discussed earlier in this section. Both recent and older datasets have been analyzed using various scale-resolving methods over the years. Early studies employed a hybrid RANS–LES approach:

  • Georgiadis, N.J., Alexander, J.I.D., and Reshotko, E., “Hybrid Reynolds-Averaged Navier-Stokes/Large-Eddy Simulations of Supersonic Turbulent Mixing,” AIAA Journal, Vol. 41, No. 2, Feburary 2003, pp. 218-229.

Subsequent studies employed the WRLES code developed by DeBonis and included upstream calculations of the wall boundary layers that generate the compressible mixing layer.

  • Mankbadi, M.R., DeBonis, J.R., and Georgiadis, N.J., “Comparison of High-Order and Low-Order Methods for Large-Eddy Simulation of a Compressible Mixing Layer,” AIAA Paper 2015-2939, Jun. 2015.

Recent work has focused on detailed analysis of the turbulent flow budget terms:

  • Debonis, J.R., “Implicit Large-Eddy Simulations of Compressible Mixing Layers,” AIAA Paper 2024-1364, Jan. 2024.

Assessment of Large-Eddy Simulation Capabilities and Needs

Inlet and nozzle researchers have authored survey papers addressing the state of the art and research needs of large-eddy simulation (LES) methods for aerodynamic flows::

  • Yoder, D.A., DeBonis, J.R., and Georgiadis, N.J., “Modeling of Turbulent Free Shear Flows,” Computers and Fluids, Vol. 117, 2015, pp. 215-232.
  • Georgiadis, N.J., Rizzetta, D.P. and Fureby, C., “Large-Eddy Simulation: Current Capabilities, Recommended Practices, and Future Research,” AIAA Journal, Vol. 48, No. 8, Aug. 2010, pp. 1772-1784.
  • Debonis, J.R., “Progress Towards Large-Eddy Simulations for Prediction of Realistic Nozzle Systems,” Journal of Propulsion and Power, Vol. 23, No. 5, Sept. 2007, pp. 971-980.
  • Georgiadis, N.J. and DeBonis, J.R., “Navier-Stokes Analysis Methods for Turbulent Jet Flows with Application to Aircraft Exhaust Nozzles, Progress in Aerospace Sciences, Vol. 42, Jul. 2006, pp. 377-418.

Read More About Inlets and Nozzles

A color map plot showing velocity difference (u−U)/ΔU across x (mm) and y (mm) axes, with color bar from blue (0) to red (1). The flow pattern varies along staggered measurement sections. Inset text: Mₑ = 0.19.

Fundamental Physics Experiments

Fundamental physics experiments increase our understanding of more complex problems and provide important data for improving and validating physical models.

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• Rendered 3D diagrams of supersonic jet engine inlets, with internal structures highlighted in yellow, showing side, rear, and angled views of various aerodynamic designs.

Design and Analysis Software

A range of advanced software tools is used to support the design, analysis, and testing of inlets and nozzles for aerospace propulsion systems.

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A metallic aircraft model mounted on a support inside a blue wind tunnel, surrounded by perforated walls and floor for aerodynamic testing.

Support of Flight Demonstration Projects

Computational fluid dynamics, wind tunnel tests, real-time displays, and system integration support X-59 supersonic flight.

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Inlets and Nozzles

NASA is advancing inlets and nozzles for aircraft engines and aerospace applications through research supporting commercial, military aircraft, and space propulsion systems.

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An aircraft model mounted on a pole inside a wind tunnel, surrounded by metallic walls with circular perforations and reflective surfaces.
X-59 Sonic Boom Test Model in the 8′ x 6′ Supersonic Wind Tunnel at NASA’s Glenn Research Center.
NASA