Laser Doppler velocimeter measurements in unsteady, separated, transonic diffuser flows

Abstract

A laser Doppler velocimeter was used to measure the stream wise velocity component in unsteady separated flowfields in a two-dimensional transonic diffuser with and without externally induced periodic fluctuations. Results are also presented for fully attached, unsteady, unexcited flow. The time-dependent perturbation flowfield associated with the external excitation was determined throughout the subsonic region for a case with shock-induced separation. The results indicate that a transverse, wavelike motion of the boundary-layer/coreflow interface is an important aspect of the overall oscillations and overwhelms effects associated with acousticwave propagation. NomenclatureA = amplitude coefficient in Fourier series / = excitation frequency h = channel height M = Mach number TV = number of velocity samples T = temperature u = mean streamwise velocity u = rms of streamwise fluctuating velocity component u = ensemble-averaged streamwise velocity u = periodic component of ensemble-averaged streamwise velocity x = dimensionless streamwise coordinate; x/h*, x-Q at throat y = dimensionless vertical coordinate; y/h*, y = 0 at lower wall a. = perturbation phase angle 5* = dimensionless displacement thickness, d*/h * c/> == phase angle in Fourier series § = dimensionless momentum thickness, B/h * Subscripts e -exit ( -lower wall m = midstream (y = 0.432) n -Fourier harmonic o = plenum r -reference s = static t = total u = upper wall o =shock * =throat

Modelling the Flow in a Transonic Diffuser with One Reynolds-Stress and Two Eddy-Viscosity Models

“…The purpose of these studies were mainly focused on the design optimization of supersonic inlets of air-breathing propulsion systems of aircraft and missiles, such as ramjets. Among others, Salmon et al [17] carried-out detailed LDA measurements for the streamwise velocity component with and without externally induced periodic oscillations. Sajben et al [18] also provided experimental data for the same diffuser with an exit-to-throat pressure-ratio of 1.52.…”

A Numerical Analysis of Supersonic Intake Buzz in an Axisymmetric Ramjet Engine

“…A series of studies was then conducted in the 1950s [2][3][4][5][6], primarily based on limited experimental measurements and linear stability analyses [2][3][4][5][6]. In the 1980s, motivated by the needs to circumvent ramjet combustion instability problems, Sajben and co-workers performed experimental studies on inlet diffuser flows with pressure oscillations [7][8][9]. Several related studies were also conducted to explore the internal flow-fields in ramjet engines, with special attention focused on the inlet aerodynamics [10][11][12] and combustion chamber dynamics [13][14].…”

Adjoint-Based Constrained Aerodynamic Shape Optimization for Multistage Turbomachines

“…The configuration was introduced by Sajben and co-workers, who studied the set-up experimentally in an effort to investigate the impact of self-excited unsteady fluctuations at inlets on the transonic flow system within a diffuser typical for supersonic aircraft propulsion systems, cf. [79,80,81,82]. The study produced a vast amount of experimental data at a variety of flow conditions, including static wall pressure distributions and velocity profiles at numerous streamwise locations, such that the Sajben diffuser became a popular test case for the verification and validation of CFD codes investigating internal compressible flows, cf.…”