Showing papers by "Terrence W. Simon published in 2011"

Experimental investigation of disc cavity leakage flow and hub endwall contouring in a linear rotor cascade.

Abstract: University of Minnesota M.S. thesis. April 2010. Major: Mechanical Engineering. Advisor: Terrence W. Simon. 1 computer file (PDF); xv, 163 pages, appendix A. Ill. (some col.)

Enhancing Heat Transfer of Air-Cooled Heat Sinks Using Piezoelectrically-Driven Agitators and Synthetic Jets

Abstract: Air-cooled heat sinks prevail in microelectronics cooling due to their high reliability, low cost, and simplicity. But, their heat transfer performance must be enhanced if they are to compete for high-flux applications with liquid or phase-change cooling. Piezoelectrically-driven agitators and synthetic jets have been reported as good options in enhancing heat transfer of surfaces close to them. This study proposes that agitators and synthetic jets be integrated within air-cooled heat sinks to significantly raise heat transfer performance. A proposed integrated heat sink has been investigated experimentally and with CFD simulations in a single channel heat sink geometry with an agitator and two arrays of synthetic jets. The single channel unit is a precursor to a full scale, multichannel array. The agitator and the jet arrays are separately driven by three piezoelectric stacks at their individual resonant frequencies. The experiments show that the combination of the agitator and synthetic jets raises the heat transfer coefficient of the heat sink by 80%, compared with channel flow only. The 3D computations show similar enhancement and agree well with the experiments. The numerical simulations attribute the heat transfer enhancement to the additional air movement generated by the oscillatory motion of the agitator and the pulsating flow from the synthetic jets. The component studies reveal that the heat transfer enhancement by the agitator is significant on the fin side and base surfaces and the synthetic jets are most effective on the fin tips.Copyright © 2011 by ASME

Separation Control Using Plasma Actuators: Steady Flow in Low Pressure Turbines

Abstract: A Dielectric Barrier Discharge plasma actuator is operated in flow over the suction surface of a Pack-B Low Pressure Turbine (LPT) airfoil at a Reynolds number of 50,000 (based on exit velocity and suction surface length) and inlet free-stream turbulence intensity of 2.5%. Measurements of total pressure using a glass total-pressure tube are taken. Corrections for streamline displacement due to shear and wall effects are made, and comparisons with previous hot-wire measurements are used to validate data. Measurements from previous work have shown that separation control is possible without stream-wise momentum addition, by adding disturbances that cause transition in the separated shear layer. The present results are from measurements taken using a glass dielectric, with a conventional two-electrode geometry, and a new three-electrode geometry. The region of high momentum flow produced due to the presence of the actuator is found to be above the shear layer, and not at the wall. The near-suction-surface total pressure field in the trailing part of the airfoil passage and its wall-normal gradient are used to demonstrate effective prevention of flow separation using the plasma actuator.Copyright © 2011 by ASME

Effects of stator/rotor leakage flow and axisymmetric contouring on endwall adiabatic effectiveness and aerodynamic loss

Abstract: The high pressure turbine stage possesses a wealth of complexities for designers to consider. One of recent interest is that of leakage (or purge) flow ejection at the stator-to-rotor interface. At this interface, a small cavity is designed into the engine to provide clearance between the rotor disk and the stator. The dimensions of this cavity can vary as a result of transient operating conditions. The ideal cavity is as small as practical. The cavity must be protected from hot gas ingression. Current designs meter flow bled from the high pressure compressor into the cavity using labyrinth seals, as shown in Figure 1. This flow, used to prevent ingression of hot gas from the passage, also offers cooling. Its interaction with the hot gas path flow as it exits the disc cavity, is the topic of this study.

A Polymeric Piezoelectric Synthetic Jet for Electronic Cooling

Abstract: Polymer synthetic jets driven by cantilever PZT bimorphs were fabricated and their cooling performance on a heat sink fin tip surface was investigated. Geometrical parameters of the synthetic jets, including cavity size, cavity depth, orifice size, orifice length, and diaphragm thickness, were optimized for increased jet velocity and high cooling performance using the Taguchi test method. Based on the test results, a synthetic jet with an optimized structure was fabricated. Measurements showed that the optimized jet can produce a peak air velocity of 50 m/s at 900 Hz from a round orifice 1.0 mm in diameter. The power consumption of the jet in this condition is 0.69 W and the total mass is 6 g. Using the optimized synthetic jet, a heat transfer coefficient of 576 W/m2 K was achieved on the fin tip, indicating an increase of 630% over natural convection values.Copyright © 2011 by ASME

A Computational Study of Active Heat Transfer Enhancement of Air-Cooled Heat Sinks by Actuated Plates

Abstract: Heat transfer performance of air-cooled heat sinks must be improved to meet thermal management requirements of microelectronic devices. The present paper addresses this need by putting actuated plates into channels of a heat sink so that heat transfer is enhanced by the agitation and unsteadiness they generate. A proof-of-concept exercise was computationally conducted in a single channel consisting of one base surface, two fin wall surfaces, and an adiabatic fourth wall, with an actuated plate within the channel. Air flows through the channel, and the actuated plate generates periodic motion in a transverse direction to the air flow and to the fin surface. Turbulence is generated along the tip of the actuated plate due to its periodical motion, resulting in substantial heat transfer enhancement in the channel. Heat transfer is enhanced by 61% by agitating operation for a representative situation. Translational operation of the plate induces 33% more heat transfer than a corresponding flapping operation. Heat transfer on the base surface increases sharply as the gap distance between it and the plate tip decreases, while heat transfer on the fin wall surface is insensitive to the tip gap. Heat transfer in the channel increases linearly with increases of amplitude or frequency. The primary operational parameter to the problem is the product of amplitude and frequency, with amplitude being slightly more influential than frequency. The analysis shows that the proposed method can be used for modern levels of chip heat flux in an air-cooled model forestalling transition to liquid or phase-change cooling.Copyright © 2011 by ASME