Accession Number:

ADA422961

Title:

Effect of Dimple Pattern on the Suppression of Boundary Layer Separation on a Low Pressure Turbine Blade

Descriptive Note:

Master's thesis Sep 2002-Mar 2004

Corporate Author:

AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING AND MANAGEMENT

Personal Author(s):

Report Date:

2004-03-01

Pagination or Media Count:

201.0

Abstract:

Three dimple patterns were investigated to ascertain their relative effectiveness on controlling boundary layer separation from a low-pressure turbine blade. The three cases included a single row of dimples at 65 of the axial chord with 2.22 cm spacing, a single row of dimples at 65 of the axial chord with 4.44 cm spacing, and a two-row staggered pattern with rows at 65 and 76 of the axial chord with 4.44 cm spacing. The multiple row case was such that the center of the upstream dimple set at the midpoint between two downstream dimples. The dimple spacing was measured center-on-center. Each of the dimple patterns was studied and compared to an unmodified blade at axial chord Reynolds numbers based on inlet velocity of 25k, 45k, and 100k. Experimental data was collected in a low-speed, draw down wind tunnel containing a linear turbine cascade of 8 Pak-B blades. Measurements of surface pressure, boundary layer parameters, wake velocity, and total pressure losses were made to examine the flow. No dimple pattern dramatically outperformed the others. Each of the dimple patterns studied improved the average total pressure loss coefficient by 34 for Re 25k and 1 Tu. Complementing the experimental effort was a three-dimensional computational fluid dynamics study. Four models were built and analyzed. The models included an unmodified blade, blades with dimples at 65 of the axial chord with 2 cm or 4 cm spacing, respectively, and a multiple row case consisting of dimples at 65 and 76 of the axial chord with 2 cm spacing. Again the upstream dimple set at the midpoint between two downstream dimples. The computational fluid dynamics study provided detailed flow visualization in and around the dimples as well as a comparison to experimental data for solver verification. It was shown that the computational and experimental results showed similar trends in wake loss and boundary layer traverses.

Subject Categories:

  • Hydraulic and Pneumatic Equipment
  • Fluid Mechanics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE