Computational Assessment of Flow through a High-Flow Nacelle Bypass

Sonic boom minimization – Important challenge

• Intensity depends on the shape and weight of aircraft
• Ex: Quiet Spike Program – updated nose geometry to split the main shock
• Engine nacelles create a sizable boom

More Details

Objectives: Assess bypass flow quality

• Full-scale simulation to identify areas of interest
• Estimates for smaller, focused simulations
• Cross-compare with independent NASA data

Computational Approach

Methodology

• Mesh generation – ICEM CFD and GAMBIT package3
• Unstructured, Structured, Hybrid meshes
• Fluent-based grid adaption
• Evaluation of optimal CFL

• Flow Solution

  • ANSYS FLUENT (v.12.0 and 13.0)
  • Steady-state or transient
  • 2nd order upwind fluxes
  • Density-based solve

Aft-Bypass: Results

• Spalart-Allmaras: predicted fully-developed turbulent velocity profile
• Transition SST Model
  • closest to experimental boundary layer profiles
  • faster convergence
  • separation predicted well by Transition SST
• Throat and constant area passage included to account boundary layer
• Results improved significantly

Conclusions

• Conducted RANS based simulations on proposed bypass concept  to attain the lower sonic boom

• Full engine solution
  • Verified against NASA data
  • Identified highly-curved channels as critical

• Aft-Bypass
  • Clean and vaned models analyzed in detail
  • Upstream BL development important
  • Predictions by Transition SST model closest to experimental results

• Single channel
  • Predicted high turbulence levels and shocks
  • Boussinesq-based turbulence models
    • overpredict turbulence production
    • may not be suited to evaluate performance metrics