Effect of Wake-Type Nonuniform Inlet Velocity Profiles on First Appreciable Stall in Plane-Wall Diffusers

Abstract

The combustor diffuser in a gas turbine engine must accept a high-speed, unsteady, distorted flow from the engine compressor. It must deliver flow to the combustor with minimum loss in total pressure and minimum velocity profile distortion. Both pressure recovery and outlet flow distortion characteristics of diffusers must be considered in design tradeoffs. The purpose of this investigation was to study the effects of nonuniform inlet velocity profiles on the inception of stall in two-dimensional plane-wall diffusers. Centrally-located “wake-type” inlet velocity profiles were chosen to simulate the flow conditions at the inlet of a combustor diffuser. The inlet distortion was characterized by dimensionless wake strength and wake width parameters. The experiments were performed on an open surface water table to make flow visualization possible. A centerline or pocket-type stall, such as previously reported in swirling flows, was observed for sufficiently severe inlet profile distortion. A new definition of first appreciable stall, based on a fraction of the exit area stalled, was introduced to characterize stalls which did not occur on a solid surface.

Further Data on the Performance of a Rectangular Diffuser in Distorted Inlet Flows

“…Fig. 1 shows two main categories and four sub categories of (6) only were carried out on two-dimensional plane wall diffusers. Both dealt with symmetrically non-uniform profiles: the first studying the effects of boundary layers, Class I, and the second the effects of the centrally located wakes, Class II.…”

“…For centrally located wakes,Fig. 1(b)-profiles (c) and (d),Kaiser and McDonald (6) introduced the following parameter: Umax(6)…”

Performance of straight-walled annular diffusers with swirling flow

“…This can make design optimisation difficult. Some investigators have attempted to provide guidance to the designer by reporting measured performance for a wide range of diffuser geometries, albeit in a specific class such as two-dimensional studies by Kline et aP~ - 1 ' and Reneau et al (5 \ conical, investigated by Cockrell and Markland' 6 ' and Sprenger 171 , and annular, reported by Sovran and Klomp <8 > and Stevens< g >. Often the designer faces space restrictions and desires the maximum pressure rise in a minimum length, but when space is not so limited, desires the maximum pressure rise for a specified area ratio.…”

Aerodynamic Research on Straight Wall Annular Diffuser for Turbofan Augmentor

“…A correlation for the velocity distribution in the diffuser was also obtained. s it is well known, the inlet velocity profile has very strong influence on diffuser performance, many researchers have published their experimental or analytical results [1][2][3][4]. So far there is little reported in the literature concerned with the effect of non-uniform velocity and temperature profile on diffuser performance.…”