Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 47-50). Also available via the Internet.

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In recent decades, greater interest in the effect of rotational wakes on gas turbine film cooling applications has produced increasing numbers of studies on these unsteady phenomena. Wakes are primarily shed from upstream components such as transition duct walls, stator vanes, and rotors. Studies have shown that in areas of unsteady flow, the best performing parameters in conventional steady investigations may not be the best for unsteady applications. One common method of modeling the unsteady wake interaction in subsonic flows is the use of spoke wheel type wake generators using cylindrical rods to produce the velocity detriment and local increase in turbulence intensity. Though the impact of wakes have been studied for decades on airfoil losses and boundary layer transition, only recently has the film cooling and wake interaction been investigated. The existing work is primarily on leading edge models and airfoil cascades. The primary parameter characterizing the unsteady wakes is the dimensionless or reduced frequency known as the Strouhal number. The film cooling jet itself has dominant frequencies resulting from the shear and the jet trailing wake shedding, depending on the injectant flow rate. There exist great deficiencies in the fundamental understanding of the interaction of these two frequencies. Heat transfer considerations are also relatively recent being studied only since the early 1990's. Heat transfer coefficients and film cooling effectiveness have been reported for leading edge and linear airfoil cascades. In the case of the linear cascade, no data can be taken near the endwall region due to the varying tangential velocity of wake generating rod. The current work expands on this initiative incorporating a sector annular duct as the test setting for the rotating wakes focusing on this endwall region.; Studies in to the effect of the rods in this alternate orientation include film cooling effectiveness using temperature sensitive paint, impact of wake rod to film cooling hole diameter ratio, and time accurate numerical predictions and comparisons with experimental work. Data are shown for a range of momentum flux ratios and Strouhal numbers. The result of this work sets the stage for the complete understanding of the unsteady wake and inclined jet interaction.

Steady and unsteady flow over a generic Suboff submarine model is studied. The skin-friction magnitudes are measured by using hot-film sensors each connected to a constant temperature anemometer. The local minima in the skin-friction magnitudes are used to obtain the separation locations. Steady static pressure measurements on the model surface are performed at 10° and 20° angles of attack. Steady and unsteady results are presented for two model configurations: barebody and sail-on-side case. The dynamic plunge-pitch-roll model mount (DyPPiR) is used to simulate the pitchup maneuvers. The pitchup maneuver is a linear ramp from 1° to 27° in 0.33 seconds. All the tests are conducted at ReL=5,500,000 with a nominal wind tunnel speed of 42.7±1 m/s. Steady results show that the flow structure on the leeward side of the barebody can be characterized by the crossflow separation. In the sail-on-side case, the separation pattern of the non-sail region follow the barebody separation trend closely. The flow on the sail side is strongly affected by the presence of the sail and the separation pattern is different from the crossflow separation. The flow in the vicinity of the sail-body junction is dominated by the horseshoe type separation. Unsteady results of the barebody and the non-sail region of the sail-on-side case show significant time lags between unsteady and steady crossflow separation locations. These effects produce the difference in separation topology between the unsteady and steady flowfields. A first-order time lag model approximates the unsteady separation locations reasonably well and time lags are obtained by fitting the model equation with the experimental data. The unsteady separation pattern of the sail side does not follow the quasi-steady data with a time lag and the unsteady separation structure is different from the unsteady crossflow separation topology observed for the barebody and the non-sail region of the sail-on-side case. / Master of Science

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Numerical treatments have become the most accurate methods for transient liquid flows analysis. Based on a computer code provided by NASA/KSC, this paper presents two simulations of cryogenic transfer systems. Experimental data originated from the Space Shuttle Liquid Oxygen Servicing were obtained during drain flows. Two sets of data (pressure at various locations versus time) corresponding to a drain stop and a drain initiation were used for a comparison with the predicted pressures. The first test case was a single-phase flow whereas the second one was associated with liquid-column separation and vapor cavity collapse. Major modifications were made to the computer program for two-phase flow treatments. Encouraging results have been obtained validating the model and opening new perspectives for future work.

Studies on the effect of transport properties coupled with the interaction of fluid dynamics and combustion in acoustically forced laminar hydrogen jet diffusion flames have been performed using the planar laser-induced fluorescence (PLIF) technique. These unsteady diffusion flames are of particular interest because they are reproducible turbulent-like events that can be investigated to gain insight into turbulent combustion. Results reported herein add to the ongoing effort of understanding the complex transport processes taking place in the flames encountered in most modern heat-producing and power-producing devices. Fuel transport properties (i .e. fuel Lewis number, LeF) were varied by fuel dilution with various levels of helium (He) or argon (Ar). The fuel stream ofBurkeSchumann type hydrogen flames was acoustically excited by using a loudspeaker and the two-dimensional OH and temperature fields were measured. PLIF measurements were performed using an intricate two-laser, two-camera system; digital image analysis was implemented to reduce the large image data set obtained. The temperature of the unsteady flames departed significantly from the steadystate temperature as predicted by previous researchers. It was found that, regardless of LeF, unsteady He-diluted flames had maximum flame temperatures at some point during the speaker -oscillation that were always higher than the maximum temperatures of the H2-Ar flames. This was contrary to the trends seen in steady flames. An increased H2 mass flux to the flame zone in the unsteady H2-He flames was the reason for this observation since mass diffusion becomes important in the driven flames due to increased mass gradients and the difference in diffusivity of hydrogen in the diluents used. Low turbulence intensities (i.e.low frequency) allowed the flames to respond steadily to the changing flowfield. The structure of the reaction zone of unsteady flames at this low frequency was altered (i.e. stretched or compressed) slightly and, in general, these flames resembled the steady flames structurally. At high frequency, however, the flames responded to the imposed flow oscillation by considerable reaction zone stretch/compression. Results obtained from the present experiments suggest that, depending on the Lewis number, the flame temperature responds differently to the stretch imparted on the flame by the unsteady flowfield. These Lewis number effects were evidenced by both the low and high frequency flames, however, they were most obvious in the high frequency cases. The temperature of flames with LeF ~ l increased/decreased when the reaction zone thickened/thinned. On the other hand, flames with LeF < l increased/decreased in temperature when the reaction zone thinned/thickened. These trends competed with the thermal and mass transport processes present in the high-curvature regions of the flames.

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