A study of tunnel boundary interference in a perforated wall wind tunnel using a panel method

The objective of this study is to find a fast and effective method of estimating tunnel boundary interference for a subsonic perforated wall wind tunnel. The study consists of three parts. In the first part, a theoretical approach is investigated for finding the boundary interference solutions which utilize both the wall interference and free-air model potential functions, and could be placed into a modified PMARC code for use with perforated walls. This theoretical method involved three steps which could be compared with each other in order to check the process. The first and second steps of the theoretical method dealt with solid wall wind tunnels while the last step used a perforated wall wind tunnel. The final results for the last step were compared and plotted against various values for the porosity coefficient to examine the sensitivity of the solution with respect to the value of porosity. The second part of the study used the equations and method which were proved in the first part to modify the panel code PMARC for perforated wall wind tunnels. The modified PMARC code was then used to predict the boundary interference in various wind tunnels with uniform porosities. The values found in the second part were compared with known values and the results were found to be of good agreement. The third part of the theoretical study used the panel code obtained in the second part and continued the modifications to include distributed porosities along the length of the wind tunnel. A study was performed which used very low values, between 0.05 and 0.2, for the porosity of the upstream portion of the wind tunnel test section, and values near the exit of the test section were set between 0.25 and 0.35. The tunnel boundary interference was calculated by the modified PMARC code and these values were compared with the values found in the second part. As expected, the predicted values for tunnel boundary interference decreases as the porosity of the upstream portion of the test section is reduced and the porosity near the exit is increased.