Analysis of wind tunnel model support system vibration

A number of wind tunnel test facilities are experiencing undesirable vibrations of the model support system. These vibrations lead to a number of problems. For example, when the model vibrates, the test conditions are no longer realistic. The dynamics of the model and sting cause the flow to become unsteady. The data collected from unsteady flow differs from that collected when the flow is steady state. Another major concern is that the vibrations could cause the model to come apart and damage components inside the wind tunnel, such as compressors or blades, which could be costly to repair. Therefore, limitations are placed on the conditions at which the tunnel can be operated. In order to reduce the vibrations in the wind tunnel, the vibration must first be measured, which will be the primary topic of this paper. The purpose of this thesis was to design a generic model support system that closely represents a typical wind tunnel model support system (sting, balance, and a generic model), measure the vibration in the model support system, perform modal analysis, and compare the results with finite element modeling. Passive damping techniques were also explored experimentally. Several experimental methods were considered as options to measure deflection of a vibrating beam. This study utilizes a cylindrical beam as a simplification of the sting problem. Three experiments were conducted, and finite element analysis was performed on the model. Experimental results showed that the model behaved similar to a typical wind tunnel model. They also showed that the insertion of a sleeve around the sting could be an effective way to attenuate the frequency, once improved. Finite element solutions obtained were generally in good agreement with the results from the experiments.