# University of Minnesota

Aerospace Engineering and Mechanics

**Fall 2000 Seminar Series**

*On the
Relationship Between the Wall Pressure and the Velocity Field in a Turbulent
Boundary Layer* *

*Abstract*

**Two sets of experiments were performed to
investigate the coupling between the flowfield and wall pressure in a turbulent
boundary layer. In the first, a stochastic estimation technique on the
streamwise velocity field was implemented for the cases of high-amplitude wall
pressure conditions. The comparisons of both the linear and quadratic estimate
to the conditional average provides insight into the dependence of the wall
pressure on the linear and non-linear source terms in Poisson's equation. It is
shown that the quadratic stochastic estimation technique approximates the trend
and the magnitude of the conditionally-averaged velocity fluctuations very
well; whereas, the linear stochastic estimation underestimates the magnitude of
the velocity, for both positive and negative wall-pressure detections. This
suggests that the non-linear source terms are important in the generation of
the wall pressure. The second investigation concerns the correspondence between
the conditionally averaged and instantaneous flow. High-resolution PIV,
simultaneously acquired with an array of wall-pressure sensors, provided
several independent realizations of the instantaneous flowfield and associated
wall pressure. A large-scale shear layer is evident for both positive as well
as negative wall-pressure events where fluid with positive momentum is upstream
of fluid with momentum deficit. For the case of a positive wall pressure
detection, p¢w/p¢wrms ³ +2.5, the streamwise location of the
shear layer in the region close to the wall coincides with the detection point
of the maximum wall pressure signal; whereas, the shear layer is displaced in
the streamwise direction by » 400 wall units for
p¢w/p¢wrms£ -2.5. **

### Friday,
November 10, 2000

209 Akerman
Hall

2:30-3:30 p.m.

### Refreshments served after the seminar in
227 Akerman Hall.

Disability accomodations provided upon request.

Contact Kristal Belisle, at (612)
625-8000.

*** This work was supported under grants from the Office of Naval Research,
NASA Space Grant and National Science Foundation.**