Accession Number : ADA320023

Title :   Receptivity in Boundary-Layer Transition to Turbulence.

Descriptive Note : Final rept. 15 Oct 93-14 May 96,

Corporate Author : ARIZONA STATE UNIV TEMPE DEPT OF MECHANICAL AND AEROSPACE ENGINEERING

Personal Author(s) : Saric, William S.

PDF Url : ADA320023

Report Date : AUG 1996

Pagination or Media Count : 244

Abstract : Experiments are conducted in the Arizona State University Unsteady Wind Tunnel to investigate acoustic receptivity in the leading-edge region of a Blasius boundary layer. The experiment utilizes two different flat-plate models. One model has a leading edge with a special geometry that limits the receptivity mechanism to the leading edge. The second model is a tapered elliptical-leading-edge flat plate with a junction. A Blasius basic state isolates the instability mechanism to a Tollmien-Schlichting wave and symmetric flow around the leading edge is established for each model. The acoustic disturbances are digitally generated and broadcast into the test section creating sound pressure levels ranging from 90 to 130 dB. Several techniques are examined for separating the Tollmien-Schlichting wave from the background noise. These include hot-wire signal separation in the complex plane, the Kendall differential microphone, a multiple-microphone technique, and a sound burst technique. Receptivity coefficients show the same focusing characteristics of the T-S wave amplitude for a narrow band of frequencies documented in previous experiments. This suggests that the focusing behavior is not due to the special geometry of tl0e leading edge. Boundary-layer measurements indicate some spanwise variation that could contribute to the focusing behavior. The work is now extended to include very high disturbance levels.

Descriptors :   *TURBULENCE, *BOUNDARY LAYER TRANSITION, SIGNAL PROCESSING, ACOUSTIC WAVES, TURBULENT FLOW, WIND TUNNEL TESTS, ACOUSTIC MEASUREMENT, LEADING EDGES, FLOW NOISE, FREE STREAM, LAMINAR FLOW, SOUND PRESSURE, REYNOLDS NUMBER, BACKGROUND NOISE, SKIN FRICTION, ACOUSTIC FIELDS, BOUNDARY LAYER FLOW, FLAT PLATE MODELS, SOUND RANGING.

Subject Categories : Fluid Mechanics
      Acoustics

Distribution Statement : APPROVED FOR PUBLIC RELEASE