Type of Document Master's Thesis Author Rusche, Max Thomas URN etd-08252011-081702 Title Structure of Turbulent Boundary Layers and Surface Pressure Fluctuations on a Patch of Large Roughness Elements Degree Master of Science Department Aerospace and Ocean Engineering Advisory Committee
Advisor Name Title Simpson, Roger L. Committee Chair Devenport, William J. Committee Member Schetz, Joseph A. Committee Member Keywords
- surface pressure
- velocity spectra
- boundary layer
Date of Defense 2011-07-28 Availability unrestricted AbstractMeasurements were made in a zero pressure gradient turbulent boundary layer over two
roughness patches containing hemispherical and cubical elements. The elements were 3
mm in height and spaced 16.5 mm apart in an array containing 7 streamwise rows and 6
spanwise columns for a total of 42 elements per patch. The boundary layer thickness was
approximately 60 mm, so the ratio of element height to that thickness was a large amount
at k= = 1=20. A three velocity component laser Doppler velocimeter measured instantaneous
velocities. Mean flow and turbulence statistics were calculated as well velocity
energy spectra. Surface pressure fluctuations were measured using a two-microphone
The results show that hemispherical elements produce larger turbulence quantities in
their wakes compared to the cubes. This is due to the hemispheres having a frontal area
nearly 60% larger than that of the cubes. The turbulence levels behind the hemispheres
is a maximum behind the first streamwise row of elements, and decreases afterwards.
The cubical elements maintain a nearly constant amount of turbulence in their wake,
signifying little interaction between cubical elements. Surface pressure fluctuations vary
little in the streamwise direction of the patches. The hemispherical elements produce
a larger sound pressure level behind them than the cube elements do. Velocity spectra
results show large normal stress energy for regions at and below the element height. The
energy for locations high in the boundary layer increases as the flow moves downstream.
Coherency plots show that there is a large correlation between the turbulent structure and
production of shear stress at the roughness height. Any measurements taken at or below
the roughness height are highly correlated under 10 kHz, while locations higher in the
boundary layer are correlated under 2 kHz.
Filename Size Approximate Download Time (Hours:Minutes:Seconds)
28.8 Modem 56K Modem ISDN (64 Kb) ISDN (128 Kb) Higher-speed Access Rusche_MT_T_2011.pdf 26.30 Mb 02:01:45 01:02:37 00:54:47 00:27:23 00:02:20
If you have questions or technical problems, please Contact DLA.