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


  • 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


  • 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

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