Support system interference on wall pressure in a wind tunnel using a panel method

A study was conducted in order to determine the support system interference on the wall pressures in the NASA Ames 12 foot pressure wind tunnel. The influence of the support system on the wall pressures must be determined in order to accurately correct for blockage and lift effects due to the presence of the walls. A panel method code, PMARC, was used to determine if the support system, consisting of a strut and sting and a bi-pod type support, influenced the static pressure measurements at the wall of the tunnel near the model position. The NACA 4412 airfoil was used to examine the accuracy of the code. A two-dimensional case was compared with results from another panel code, VSAERO. A three-dimensional case was compared with published data for this airfoil. The results from these calculations agreed with published data obtained both with another panel code and from actual experiments. Inviscid theory was used to explain a velocity spike encountered at the entrance to the diffuser. The calculations were performed for two different sizes of a model attached to the strut and sting support. An analysis was performed to determine the effect of the presence of a wake from the bi-pod support on the wall pressures. A model was not used in conjunction with the bi-pod support. The results of this investigation show that the sting and strut support does not influence the static pressures measured along the wall around the model location. The bi-pod support was shown to have a larger influence on the wall static pressures due to the fact that it is located directly under the model.