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No description available.

In this work, we have numerically studied the effect of the vorticity on the enhancement of heat transfer in a channel flow. In the first part of the work, we focus on the investigation of a channel flow with a vortex street as the incoming flow. We propose a model to simulate the fluid dynamics. We find that the flow exhibits different properties depending on the value of four dimensionless parameters. In particularly, we can classify the flows into two types, active and passive vibration, based on the sign of the incoming vortices. In the second part of the work, we discuss the heat transfer process due to the flows just described and investigate how the vorticity in the flow improves the efficiency of the heat transfer. The temperature shows different characteristics corresponding to the active and passive vibration cases. In active vibration cases, the vortex blob improves the heat transfer by disrupting the thermal boundary layer and preventing the decay of the wall temperature gradient throughout the channel, and by enhancing the forced convection to cool down the wall temperature. The heat transxfer performance is directly related to the strength of the vortex blobs and the background flow. In passive vibration cases, the corresponding heat transfer process is complicated and varies dramatically as the flow changes its properties. We also studied the effect of thermal parameters on heat transfer performance. Finally, we propose a more realistic optimization problem which is to minimize the maximum temperature of the solids with a given input energy. We find that the best heat transfer performance is obtained in the active vibration case with zero background flow.

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A spectral shallow water model is used at the 850 mb level to investigate the effects of cyclonic vorticity on heating in the lower troposphere and how this in turn causes an increase in cyclonic vorticity generation, creating a nonlinear vorticity feedback mechanism. The model is initialized with NCEP-NCAR reanalysis data from the period 1990-2003 and then used to simulate a heating forcing function centered in east Africa. The model is simulated using a Gaussian damped basic state, a zonally symmetric basic state, and a zero basic state. The heating forcing function is applied to these different basic states with a scaled mass sink to simulate heating in the atmosphere. The heating forcing function creates a vorticity feedback mechanism that increases cyclonic vorticity. The analysis of these different basic states shows that the Gaussian damped basic state reduces the amplitude of the observational fields at the poles, increases the observational fields in the tropical region and increases the stability of the model at shallow depths. The zero basic state does have a significant effect on cyclonic vorticity generation, but does not improve the capability of the wave to propagate westward into the Atlantic Ocean. The zonally symmetric basic state succeeds in increasing the amount of cyclonic vorticity generated. The zonally symmetric basic state, once the vorticity non-feedback region is extended, is also very effective at increasing the amount of cyclonic vorticity generated and increasing the propagation of this wave westward into the Atlantic Ocean. The analysis suggests that the vorticity feedback mechanism created by the heating forcing function is affected by cyclonic vorticity when a zero and zonally symmetric basic state are used.

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The initial rotation of flat, rectangular plates in quiescent flow were studied experimentally using two-dimensional and stereoscopic particle image velocimetry. The study examined the vortex dynamics of spanwise vorticity created on the upper, leeward surface of each plate of aspect ratio 2 and 4, which consists primarily of a leading-edge vortex. Reynolds numbers of 4,000, 8,000, and 16,000 based on the tip velocity and angles of attack of 25°, 35°, and 45° were investigated at five different azimuthal locations (90°, 180°, 235°, 270°, and 320°). The 25% and 50% spanwise positions for the aspect ratio 4 plate and 50% spanwise position for the aspect ratio 2 plate were studied. For the 25% and 50% spanwise location for the aspect ratio 4 and 2 plate, respectively, the leading-edge vortex structure's shape and coherence appear to be evolving temporally as the plate begins its initial motion. Leading-edge vortex circulation measurements confirm there is a non-monotonic trend showing increasing values until an azimuthal position of approximately 220° where there is a dip in the circulation values, but the circulation then rises towards the end of the range of azimuthal positions investigated. A strong region of counter-rotating vorticity was observed on the surface of the plate beneath the leading-edge vortex from the interaction of the leading-edge vortex with the plate. It was hypothesized that the interactions between the leading-edge vortex and counter-rotating vorticity are an important factor in governing the dynamics and strength of the leading-edge vortex which may ultimately determine whether the leading-edge vortex remains attached. To validate this claim, a transport analysis of the vorticity in the leading-edge vortex was developed to determine the contributions of spanwise flux, tilting of in-plane vorticity components, the shear layer, and annihilation has on the rate of change of circulation of the leading-edge vortex in the spanwise direction. Results of this analysis indicate that annihilation of the leading-edge vortex from entrainment of the counter-rotating vorticity is an important factor in governing the dynamics of the leading-edge vortex.

Detailed measurements were taken downstream of several modified trailing edge configurations designed to impart streamwise velocity into the flow behind a cascade of GE Rotor B fan blades. These measurements were conducted in the Virginia Tech Low Speed Linear Cascade wind tunnel. The trailing edge configurations tested utilized passive techniques for producing streamwise vorticity, which in turn causes downstream wake diffusion and increased mixing. A more diffuse wake, when it impinges on the downstream stator, will produce lower noise levels as a result of this rotor-stator interaction. Furthermore, increased mixing in the flow will reduce the levels of turbulence kinetic energy observed downstream of the blade trailing edge. Thus, this project seeks to identify which passive techniques of imparting streamwise vorticity are most effective at improving the flow characteristics responsible for some of the noise production in modern jet aircraft. The three trailing edge configurations tested in detail for this project showed significant ability to widen and stretch the downstream wake by utilizing vorticity generation techniques. The TE-8 configuration was the most effective at increasing the wake width downstream of the trailing edge. Additionally, each configuration was able to successfully reduce some of the turbulence kinetic energy levels observed downstream when compared to the baseline blade, the most effective configuration being TE-8. Finally, the momentum thickness of each configuration was measured. When compared to the baseline, the TE-1 configuration showed an increased momentum thickness, TE-8 showed little change, and TE-7 actually showed an improved momentum thickness value. / Master of Science

Quartz-rich mylonites present along the Moine Thrust Zone are well suited for the application of various analytical techniques designed for investigating the flow processes by which rock deformation occurred. These analytical techniques were applied to a suite of samples from the footwall and hangingwall of the Moine thrust exposed along the Allt Pol aâ Mhadaich stream located in the northern part of the Assynt window. Vorticity analyses were performed to determine the relative contributions of pure and simple shear deformation within the penetratively deforming thrust sheets. Integration of vorticity data with 3D strain analyses demonstrated that sub-vertical shortening perpendicular to the flow plane, accompanied by thrust transport parallel extension, occurred during mylonitization, and was driven by emplacement of the overlying Moine nappe. Quartz c-axis fabrics in the mylonites are characterized by well-defined asymmetric Type-1 cross girdles in which internal and external skeletal asymmetries are indicative of a top-to-the-WNW shear sense, compatible with regional thrusting. These c-axis fabrics were also used to estimate deformation temperatures. Differential flow stresses associated with mylonitization were estimated from the grain size of dynamically recrystallized quartz. Deformation temperature and flow stress data were then incorporated into a dislocation creep flow law for quartz to estimate strain rates. Finally, along strike variation in these flow properties at the base of the Moine nappe to the north and south of the APM section were investigated and results from the APM section compared with previously published studies of mylonites exposed in eastern Assynt that occupy similar structural positions. / Master of Science