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Computational Fluid Dynamics Simulation of Hypersonic Engine Components

by

Jack R. Edwards

Associate Professor

Department of Mechanical and Aerospace Engineering

North Carolina State University, Raleigh, NC

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Overview

Computational fluid dynamics simulation of hypersonic engine components – a major research thrust area in Aerospace Engineering at NCSU since the Mid 1980s.

Current areas of emphasis:

• Nose-to-tail simulations of complete engine flowfields (NASA Glenn; Edwards and McRae)

• Modeling of turbulent Schmidt number and Prandtl number effects in supersonic combustion (NASA Langley; Hassan and Edwards)

• Modeling of supercritical-fluid and barbotage injection of hydrocarbon fuels (AFRL/PRA; Edwards)

• Algorithmic enhancements to NASA’s VULCAN flow solver (NASA Langley; Edwards and McRae)

• Hybrid large-eddy / Reynolds-averaged modeling of scramjet component flowfields (NIA Seed Grant; Edwards)

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Personnel

Dr. Jack R. Edwards, Associate Professor

• CFD algorithm development for reacting / multi-phase flows Dr. Hassan A. Hassan, Professor

• Transition and Turbulence Modeling Dr. D. Scott McRae, Professor

• Solution Adaptive Gridding Methods

Jason Norris, Keith McDaniel, Ming Tian: Ph.D. students Ana Pinto, Michael Schoen: M.S. students Adam Amar: Undergraduate research assistant

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Unique Contributions

Low-Diffusion Flux-Splitting Schemes (LDFSS)• High-resolution upwind-differencing methods

• Extensions for real fluids, gas-solid flows, multi-phase mixture flows, chemically reacting flows, etc

• Several parallel, multi-block, implicit flow solvers built around LDFSS techniques

k- Transition / Turbulence Models• Coordinate-invariant two-equation model for wall-bounded and

free-shear flows at all speeds

• Transition model accounts for Tollmein-Schlicting, crossflow, bypass, and second-mode disturbance growth

• Predicts onset and extent of transition and has been coupled with

the Spalart-Allmaras and the k- model

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Unique Contributions

Dynamic Solution-Adaptive Gridding Techniques• Improved feature resolution through point-clustering

• Extensions for time-accurate flows, multi-block grids with non-contiguous interfaces, unstructured grids

• Recent applications to high-speed inlet unstart and pollutant source tracking in air-quality models

Hybrid Large-Eddy / Reynolds-Averaged (LES/RANS) Simulation methods• Techniques combine RANS strategies near solid surfaces with

LES strategies further away

• Transition facilitated by flow-dependent blending functions

• Applications to shock / boundary layer interactions in internal flows

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Resources

NCSC IBM SP-2 (720 processors, 1 teraflop; soon to be replaced with a linux Beowulf cluster)

4-processor Compaq ES-40 2-processor Microway DS-20 1-processor Compaq XP-1000 Several Sun, SGI workstations Several PCs LaTEX, Tecplot, Ensight, animation software VULCAN (NASA Langley), CHEM3D (Dow Chemical) REACTMB variants (NCSU) All codes parallelizable with MPI message-passing

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High-Speed Propulsion

Time-dependent simulations of Scramjet inlet / isolator / combustor interactions

Nose-to-tail simulations of NASA Glenn’s GTX Rocket-Based Combined-Cycle engine concept

Addition of time-derivative preconditioning and parallel implicit schemes to NASA’s VULCAN flow solver

Simulation of injection of supercritical fuels Simulation of aerated-liquid injection of hydrocarbon

fuels (Barbotage)

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Independent Ramjet Stream Cycle in RBCC Engines

Injectors add fuel to the incoming air. Mixing in ramjet stream precedes ignition. Thermal throat is present. Location of thermal throat can be modulated by variations in fuel injection.

Thermal ThroatFlame Front

Rocket exhaust

Fuel injection and premixing

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Rocket-Based Combined-Cycle Simulations

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Rocket-Based Combined-Cycle Simulations

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Rocket-Based Combined-Cycle Simulations: Rocket-shutoff with Nitrogen Purge

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Aerated-liquid (Barbotage) injection experiments

The Air Force Research Lab (AFRL) aerated-liquid injector is schematically illustrated in Fig. 01;

Rectangular configuration with a dimension of 6.4 mm x 2.0 mm;

A square cross section with dimension, D, of 2.0 mm used for the final discharge passage, L/D=20, converging angle θ=50°;

Water as the test liquid, and nitrogen as the aerating gas.

Fig. 01, Schematic of the injector assembly and internal flow structure

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Volume fraction contours (GLR = 0.08%)

Bernoulli inflow B.C. for the liquid phase

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GLR=2.45% Photos and simulations

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Hybrid LES/RANS Simulation Techniques

General approach: unsteady RANS (Reynolds-Averaged Navier-Stokes) near solid surfaces – LES (large-eddy simulation) in outer part of the boundary layer and in free-shear layers

Transition between RANS / LES based on flow-dependent blending functions based on ratios of turbulence length scales – best results when transition occurs in outer part of log layer

RANS models: k- and Menter’s k-

LES subgrid model: Yoshizawa’s one-equation SGS model

Applications to cavity flameholder configurations, flow behind projectiles, shock / boundary layer interactions

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Hybrid LES/RANS Simulation Techniques

Instantaneous axial velocity (25 degree compression / expansion corner)

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Hybrid LES/RANS Simulation Techniques

x', cm

pw/p

-5 0 50.5

1

1.5

2

2.5

3

3.5

4

4.5

5EXPHybrid (k-, F=F3, fine grid)Hybrid (k-, F=F3, coarse grid)RANS (k-)

Wall pressure distributions (25 degree compression/ expansion corner)

u/uey',cm

0

0.1

0.2

0.3

0.4

0.5

0.6

ExpHybrid (k-, F=F3, fine grid)Hybrid (k-, F=F3, coarse grid)RANS (k-)

x' = 1.25 cm 2.35 cm 3.10 cm

1 1 10

Velocity profiles in recovery region (25 degree compression / expansion corner)

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NIA-Sponsored Work

Primary Goal: to extend earlier work in hybrid LES/RANS simulations to three-dimensional flows characteristic of dual-mode scramjet engines

Year 1 accomplishments

• Addition of generalized multi-block capability to hybrid LES/RANS solver

• Addition of full reactive-flow capability

• Development of better blending functions to shift modeling from unsteady RANS to LES

Test cases underway:

• Investigation of separation-shock unsteadiness in compression-corner interactions

• Simulation of reactive flow downstream of UVA single-ramp, dual-mode injector using hybrid LES/RANS

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NIA-Sponsored Work: Separation-Shock Unsteadiness

Prediction of response of turbulent boundary layer to shock interaction (representative of high-speed flows within inlet / isolator configurations)

Large-scale, low-frequency unsteadiness of regions of shock-separated flow observed in experiments

Can hybrid LES/RANS methods predict this type of unsteadiness?

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NIA-Sponsored Work: Separation-Shock Unsteadiness

Time-dependent surface pressure contours

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NIA-Sponsored Work: Separation-Shock Unsteadiness

Average surface pressure distributions PDF of separation-shock position

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Leveraging NIA-Sponsored Work

“Hybrid LES/RANS Simulations of Complex Internal Flows with Multiple Shock / Boundary Layer Interactions” Edwards and Hassan; AFOSR; pending

“Database and Model Development for Combined-Cycle Mode Transition” McDaniel, Cresci, Edwards, Goyne, O’Brian, Riggins, Schetz; NASA NGLTP; pending (submitted by NIA)

MURI White Paper on Combined Cycle Engines, Frankel, Edwards,

McDaniel, Goyne, Hanson, Sung, Dutton, Loth; AFOSR; pending

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Challenges

Demise of North Carolina Supercomputing Center (July 1, 2003) – loss of 720 processor IBM SP-3

Mitigation strategies:

• 32 processor IBM P690 (NCSU)

• 32 processor IBM Bladecenter (NCSU)

• 128 processor IBM Bladecenter (NCSU; under construction; expandable)

• Access to 1024 processor IBM SP-3 at Oak Ridge National Laboratories

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Simulation of a time-dependent coatings process

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Pollutant Capture in Circulating Fluidized Beds

Three-phase system: two solids phases, one multi-component gas phase

Sub-models for fine particulate matter agglomeration, sulfur dioxide sorption, mercury capture onto activated carbon

High-resolution LDFSS extension for separated gas-solid flows

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Solids voidage time evolution

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Fine PM number density time evolution

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Fine PM flow rates

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Supercavitating water flow about a projectile

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New Directions

Atmospheric turbulence modeling and solution-adaptive meteorological simulations

Level-set methods and immersed-boundary algorithms

• Human-induced contaminant transport

• Diesel engine injector simulations

• Two-phase bubble dynamics Hybrid LES/RANS simulations of

• Shock-train propagation

• Ramped-injector flowfields

• Biological systems (lung bronchii, aortic aneurisms)

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Level-Set / Immersed Boundary Methods: 2-D Simulation of “feet” moving in a box filled with air