Flow-field, Acoustic and Structural Interaction behind a Ramped Step.

Authors: Murugappan, S., Mihaescu, M, DiMicco, R.G., Gutmark, E., Landmann, , Treiber, , Anderson, B.
Document Type: Article
Pubstate: Published
Journal: 45th AIAA Aerospace Sciences Meeting and Exhibit.
Volume: AIAA 2007-1325   18 pages
Year: 2007


The current manuscript is a subset of a larger database where fluid-acoustic and structural vibrations were obtained behind three bluff bodies (cylinder, ramp and vortex generator). The main goal of this effort was to study the effect of shape, orientation, length scales of the protrusion, Mach number and Boundary layer effects behind the bluff body. In the current paper we discuss the fluctuating wall pressure at a low Mach number behind a ramped step. Two ramps with step heights of 0.3 and 1 inches were studied. Data were acquired for two Mach numbers (M=0.15, 0.2) and two boundary layer thicknesses (BLT=38 and 107mm) of the incoming flow. Large Eddy Simulation (LES) and 2D PIV were performed for a single ramped step case (25.4mm step height, M=0.15 and BLT=38mm). Both the mean axial velocity profiles and the separation length compared well with 2D PIV flow. Three regions were identified behind the step: shear layer emanating from the ramped step surface, a recirculating region in the ramped step wake and the reattachment zone where the separated flow reattaches to the wall. Dynamic pressure measurements indicate lower sound pressure levels behind the ramped step in the recirculating region, while the fluctuating pressure level reached as high as 145dB near the reattachment point. The use of dynamic pressure scaling was found to collapse the wall fluctuating pressure data well for a given boundary layer thickness and ramp height with varying Mach number. Increasing the BLT from 38mm to 107mm was found to decrease the peak magnitude of the pressure fluctuation near the reattachment point for both the ramp cases.