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This dissertation presents measurements of unsteady surface pressure on airfoils encountering flow disturbances. Analysis of measurements made on an airfoil immersed in turbulence and comparisons with inviscid theory are presented with the goal of determining the effect of angle of attack on an airfoils inviscid response. Unsteady measurements made on the surface of a linear cascade immersed in periodic flow are presented and analyzed to determine the relationship between the blades inviscid response and tip leakage vortex strength. Measurements of fluctuating surface pressure were made on a NACA 0015 airfoil immersed in grid generated turbulence. The airfoil model has a 2' chord and spans the 6' Virginia Tech Stability Wind Tunnel test section. Two grids were used to investigate the effects of turbulence length scale on the surface pressure response. A large grid which produced turbulence with an integral scale 13% of the chord and a smaller grid which produced turbulence with an integral scale 1.3% of the chord. Measurements were performed at angles of attack from 0 to 20. An array of microphones mounted subsurface was used to measure the unsteady surface pressure. The goal of this measurement was to characterize the effects of angle of attack on the inviscid response. Lift spectra calculated from pressure measurements at each angle of attack revealed two distinct interaction regions; for reduced frequencies < 10 a reduction in unsteady lift of up to 7 decibels (dB) occurs while an increase occurs for reduced frequencies > 10 as the angle of attack is increased. The reduction in unsteady lift at low reduced frequencies with increasing angle of attack is a result that has never before been shown either experimentally or theoretically. The source of the reduction in lift spectral level appears to be closely related to the distortion of inflow turbulence based on analysis of surface pressure spanwise correlation length scales. Furthermore, while the distortion of the inflow appears to be critical in this experiment, this effect does not seem to be significant in larger integral scale (relative to the chord) flows based on the previous experimental work of McKeough (1976) suggesting the airfoils size relative to the inflow integral scale is critical in defining how the airfoil will respond under variation of angle of attack. A prediction scheme is developed that correctly accounts for the effects of distortion when the inflow integral scale is small relative to the airfoil chord. This scheme utilizes Rapid Distortion Theory to account for the distortion of the inflow with the distortion field modeled using a circular cylinder. Measurement of the unsteady surface pressure response of a linear cascade in periodic disturbance is presented. Unsteady pressure was measured on the suction and pressure side of two cascade blades with an array of 24 microphones (12 per blade side) mounted subsurface. The periodic disturbance was generated using a pair of vortex generators attached to a moving end wall. Measurements were made for 8 tip gaps (t/c = 0.00825, 0.0165, 0.022, 0.033, 0.045, 0.057, 0.079, 0.129) and phased averaged with respect to the vortex generator pair position. This measurement was motivated by the results presented by Ma (2003). The work of Ma (2003) suggested that tip leakage vortex shedding in the presence of a periodic disturbance is heavily influenced by the inviscid response of the cascade blade. This conclusion was arrived at by Ma's (2003) observation that as the tip gap is increased the amount of fluctuation in the tip leakage vortex circulation increases dramatically, in fact, many times the circulation in the inflow vortices. Unsteady pressure measurements reveal that the blade response involves a complex interaction of both inviscid response and viscous phenomena. However, a close relationship between unsteady tip loading and tip leakage vortex circulation is revealed suggesting the inviscid response is significant in determining the tip leakage vortex circulation. Additionally, predictions using inviscid theory agree well with measured levels of unsteady tip loading. As such, inviscid theory may be useful for predicting the tip leakage circulation and perhaps, pressure fluctuations in the tip leakage vortex. / Ph. D.

Evaluating the performance of filter media for filtration applications is essential to assure design engineers and users that filter device will deliver promised performance for specific applications under the environmental stress. The study of particle loading characteristics of filter media in the laboratory setting is typically performed under the steady flow conditions, i.e., at the constant particle concentration and flow rate. In reality, filtration products are operated under the situations that the flow rate and mass concentration of particles are varied in time. The success of translating the laboratory data to estimate the performance of filter media in the fields is thus limited. It is necessary to investigate the performance of filter media under the real-world conditions, i.e., unsteady flow rate and mass concentration to bridge the gap. The overall goals of this research are (1) to study the performance of filter medium under unsteady conditions (i.e., the performance of respirator filter media under simulated breathing conditions); and (2) to investigate the issue of non-uniform particle deposition on HVAC filter panels. A new experimental setup was developed to accomplish the former goal. Numerical modeling tool, Computational fluid dynamics (CFD), was applied to achieve the latter objective……