Doctoral Dissertations

Date of Award

8-1992

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Aerospace Engineering

Major Professor

Ching-Fang Lo

Committee Members

Jain-Ming Wu, Roy Schulz, Kenneth Kimble

Abstract

Two types of wall interference correction methods based on interface measurements in subsonic wind tunnel testing are investigated.

The first method, called the Two-Interface method, is derived based on a small perturbation solution of the two-dimensional potential equation in subsonic flow. The method calculates a surface pressure coefficient and angle of attack correction based on axial velocity measurements on the first interface and vertical velocity measurements on the second interface in the wind tunnel. This formulation of the Two-Interface method has two advantages over previously derived formulations when applied to a two-dimensional solid wall wind tunnel: the total amount of velocity measurements is reduced if the solid wall is selected as the second interface; axial velocities on the first interface can be measured using a static pipe. The method is applied to available experimental data and corrected surface pressure coefficients show reasonable agreement with test data recorded in unconfined flow.

The second method is called the Wall Signature method, which can be used to determine wall interference corrections in three-dimensional incompressible wind tunnel testing. Surface pressure coefficient corrections are investigated in detail in the present study. Wall pressure measurements on a limited number of locations are combined with influence functions to obtain an equivalent representation of the test article and its wake. Surface pressure coefficient corrections are calculated using the equivalent body instead of the test article.

A modification of the original wall signature method is introduced: an equivalent body is described in terms of surface panel elements and combined with an existing three-dimensional panel code to determine blockage corrections in a wind tunnel with non-rectangular cross-section. This description of the equivalent body allows a direct comparison of equivalent body and test article geometry which is more difficult to obtain if the Wall Signature method is used in its original formulation. An improvement of the wall signature analysis procedure is presented as well to make the analysis of the symmetric part of the wall signature more reliable: it is shown that the analysis of the symmetric part is more effective if a least squares fit based on a Gaussian is used. Advantages and disadvantages of both Two-Interface and Wall Signature method are compared and discussed.

The Two-Interface method can only be used if the small perturbation assumption holds. An experimental study has shown that the Two-Interface method can calculate surface pressure coefficient corrections in transonic flow with restrictions: corrections can be computed on those test article surface locations where the local Mach number is less than one as long as interface measurements are taken outside of the supersonic pocket.

The modified Wall Signature method is applicable in high angle of attack testing. Blockage corrections are obtained by calculating free-air and wind tunnel flow field of the equivalent body and by taking the difference of corresponding pressure coefficients on the surface of the equivalent body. The application of a three-dimensional panel code is necessary. Thus, the time required to calculate blockage corrections is not negligibly. Therefore the modified Wall Signature method can only be applied for post-test assessment of wind tunnel blockage effects.

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