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Computational Fluid Dynamic Studies of Certain Ducted Bluff-Body Flowfields Relevant to Turbojet Combustors. Volume 1. Time-Dependent Calculations with the k-Epsilon Turbulence Model for an Existing Centerbody Combustor.

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Final rept. 16 Aug 84-30 Sep 85,

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A numerical investigation of the near-wake region in a ducted bluff-body combustor by finite-difference computations is reported. The numerical predictions are based upon the time-dependent, compressible Navier-Stokes equations and the k-epsilon turbulence model. The standard k-epsilon turbulence model was modified to account for the nonstationary terms. The time-dependent calculations predictions addressed the nonreacting near-wake flow field of the centerbody combustor with only the annular air stream present. Flowfield predictions for a combustor inlet mass flow of 2 kgs with the time-dependent formulation incorporating the k-3psilon turbulence model show the attainment of a steady-state recirculating flow in the near wake. The slow axial migration of the recirculation vortex towards the exit boundary which was noticed in the earlier time-dependent calculations without a turbulence model is not longer present. Present results have thus eliminated the appearance of reverse flow at the exit boundary with the consequent incompatibility of the boundary conditions, and thereby the spurious shedding-like behavior observed previously. The steady-state results in the present study demonstrate internal consistency with the time-averaged measurements and predictions for the locations of the vortex center and the centerline rear stagnation point. Preliminary computations for both laminar-like and turbulent flows with time-dependent perturbations of inflow boundary conditions do not show an oscillatory behavior in the interior of the combustor.

Subject Categories:

  • Fluid Mechanics
  • Combustion and Ignition
  • Jet and Gas Turbine Engines

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