Navier-Stokes solutions for mixed compression axisymmetric inlet flow with terminal shock

Abstract

AN inlet flow with mixed external/internal compressions was simulated numerically for an axisymmetric supersonic inlet model by solving the three-dimensional, unsteady, compressible Navier-Stokes equations. A study was focused on the critical flow condition with the terminal shock positioned at the inlet throat. The computed results compared favorably with available wind-tunnel data. Contents For advanced supersonic aircraft, integrated design procedures capable of handling both the external and internal flowfields are required to treat a complete inlet system such as those shown in Fig. 1. The inviscid flow analysis of Ref. 1 indicates that viscous effects must be accounted for in the computation to achieve reasonable agreement with experimental data. For the critical flow condition, in particular, the treatment of boundary-layer bleed is needed to reduce the flow separation and to stabilize the terminal shock in the inlet throat. The present study extends the inviscid inlet flow analysis of Ref. 1 but focuses on the viscous effects on the inlet flow in the critical mode of operation and on the treatment of the boundary-layer bleed condition. A combined implicit (alternating direction scheme in the streamwise and radial directions) and explicit (in the azimuthal direction) approach of Ref. 1 is adopted to solve the unsteady, compressible Navier-Stokes equations enclosed by the Baldwin-Lomax turbulence model.2 The grid is divided into two zones of the H type covering the external (freestream) and internal (inlet) flowfields (Fig. 1). The computations were carried out in each zone interchangeably. The two zones are coupled on a common boundary along a line extending from the cowl lip to the upstream boundary. The no-slip condition for the viscous flow was imposed on the inlet surfaces. During the initial stage of time-iterativ e computation, the pressure at the inlet exit and the pressure differential across the bleed slot between the inlet and the plenum were raised gradually until the experimentally measured engine face pressure and inlet bleed-mass flow ratio were attained. The porous bleed holes of the experimental model were modeled geometrically by a single slot (Fig. 2) of the same length as the extent of the bleed holes. For the purpose of simulating the actual bleed through the porous holes, the gradient of pressure differential in the streamwise direction over the bleed slot was prescribed as the boundary condition and set equal to the experimental data.