For the purposes of defining the vision of CFD in 2030, this study will consider CFD simulation challenges for the key flow phenomena listed below. The flow phenomena are categorized by current NASA Aeronautics Directorate focus areas. Note that many of the flow simulation challenges (e.g., flow separation) are common across several vehicle classes and flight regimes, and have been listed separately under each heading.
Fixed Wing:
- Smooth body separation** Drag** Stability and control effectiveness
- Maximum lift during approach/landing
- Transonic and low speed buffet
- Boundary layer ingestion for tightly coupled airframe/engine installations
- Massive separation** Cavities** Extreme maneuvers
- Blunt components
- Dynamic stall
- Laminar to turbulent boundary layer flow transition** Natural and hybrid laminar flow control
- Viscous wake interactions and boundary layer confluence** Multi-element, high-lift flows
- Corner flows** Wing/body, wing/pylon, and pylon/nacelle juncture flows
- Reattachment
- Icing** Ice development and accretion** Performance impact
- Circulation and flow separation control** Active flow control** Powered lift
- Jet exhaust** Engine noise** Jet-flap interaction
- Sonic fatigue
- Airframe noise** High-lift** Landing gear
- Vortical flows** Vortex generators/chines
- Wake hazard reduction and avoidance
- Wind tunnel to flight scaling** Reynolds number** Model characteristics: surface, brackets, aeroelastics
Rotary Wing:
- Flow separation** Bluff bodies
- Hover download
- Dynamic stall
- Vortical flow in rotor wakes** Wake persistence for large numbers of revolutions
- Blade/vortex interactions
- Rotor structural dynamics/aerodynamics/controls interactions
- Flexible/deformed rotor blade flows
- Vibratory loads
- Rotor wake/fuselage interactions
- Flow interaction with ground
- Ground wash
- Brownout
- Rotor/Airframe interaction with ground plane
- Acoustic loading
- Non-harmonic flow/rotor control
- Multi-rotor interactions (coaxial, etc.)
- Laminar to turbulent boundary layer transition flow
- Circulation and flow separation control
- Active flow control
- Icing
- Ice accretion
- Ice shedding
- Performance impact
- Wind tunnel to flight scaling** Reynolds number
- Model characteristics
High Speed (Supersonic)
- Shock/boundary layer interactions
- Shock/expansion-jet plume interactions
- Laminar to turbulent boundary layer flow transition
- Sonic boom
- Shock wave coalescence
- Propagation through atmospheric turbulence and/or wind shear
- MDAO of low boom / low drag design / high efficiency, low distortion inlet design
- Airframe/nacelle shock/viscous interactions
- Slender wing vortex flows
- Aero-propulsive-servo-elastic interactions for slender configurations
- Engine/jet nose acoustics
- Shock-induced flow separation in inlets and nozzles (un-start)
- Store separation
- Booster staging
- Weapon drop
High Speed (Hypersonic)
- Aerodynamic heating
- Interaction with ablative materials
- Radiative heating
- Boundary layer transition
- Low density effects at high altitudes
- Strong shock/boundary-layer and shock/shock interactions
- Finite-rate gas chemistry (with a complete set of chemical reactions)
- Ionization, non-equilibrium, and plasma flows during reentry
- Subsonic and supersonic combustion in dual-mode scramjets (possibly with liquid fuel injection)
- Flow separation
- Inlets and nozzles (un-start)
- Bluff bodies
- Jet interaction with freestream flow (augmentation factor)
Engine/Propulsion System
- Integrated propulsor/airframe flows
- Unsteady flows due to turbomachinery blade row interactions
- Stage matching
- Wake mixing
- Compressor stability and rotating stall
- Secondary flows, including endwall and tip vortical structures
- Time-accurate coupled component interactions
- Multi-row rotor-stator interactions
- Main gaspath/secondary gaspath interactions
- Combustor exhaust product/turbine interactions including hot streak migration
- Aerothermal cooling/mixing flows (e.g., film cooling)
- Rotational and curvature effects on flow turbulence for rotating turbomachinery
- Transitional flows over a wide range of Reynolds number, pressure gradient, and freestream turbulence
- Real gas thermodynamic models for high temperature flows with dissociation
- Reactive flows** Fuel spray modeling (two-phase flows, liquid fuel breakup, atomization, gaseous mixing)
- Multi-regime combustion models
- Emissions modeling
- Vitiated flows
- Combustion dynamics
- Near-field acoustic sources and propagation to the acoustic farfield
- Ice accretion
- Distributed (electric) propulsion