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Title:Experimental and Mathematical Modeling of the Interaction of a Perturbed Free Shear Layer With a Flat Plate
Author(s):Merati, Parviz
Department / Program:Theoretical and Applied Mechanics
Discipline:Theoretical and Applied Mechanics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Mechanical
Abstract:A mathematical model which predicts the upstream effects of the impingement of shear layers on a solid boundary located in the linear region of the shear layer is developed. The model is compared with experimental results. The experimental results and the model suggest that the oscillations that are most amplified are those whose feedback signals from the disturbance plate are nearly in phase with the wave at the splitter plate separation edge. This causes the frequency of the oscillations to gradually decrease as the plate is moved downstream. This drop continues until a certain impingement length is reached where the oscillations can not sustain themselves and by addition of an extra wavelength between the splitter plate and plate leading edge, the phase condition is again satisfied.
The effect of a plate located in the nonlinear region on the flowfield of a shear layer is investigated experimentally. This phase of the study places emphasis on the three main regions of the shear layer flow interacting with a plate: the impingement region, the plate region and the wake region. The leading edge of the plate produces large vertical velocities near the stagnation point, but further downstream, the plate is an obstruction for the vertical motion of the flow. The large structures are shifted toward the slower stream in the neighborhood of the plate. Turbulent fluctuations are damped above the plate and enhanced below the plate. At large angles of attack of the plate with respect to the incoming vortices, the high speed stream generates high pressure in the vicinity of the stagnation point on the plate and deflects the mixing layer toward the slower stream.
Measurements are obtained using single and X-sensor probes. A mathematical model for the response of slant sensor probes is developed and a general form for the slant sensor response equation is derived. The results are applied to X-sensor probes and orthogonal triple sensor probes. Interestingly, the X-sensor probes suffer increased flow disturbances, whereas the triple sensor geometry enjoys a cancelling effect which reduces the net flow disturbance despite the additional prongs. The model includes an explanation for speed dependence of the pitch coefficient.
Issue Date:1985
Description:179 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1985.
Other Identifier(s):(UMI)AAI8521834
Date Available in IDEALS:2014-12-16
Date Deposited:1985

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