Showing papers by "Richard J Goldstein published in 2007"

Heat Transfer Study in a Linear Turbine Cascade Using a Thermal Boundary Layer Measurement Technique

Abstract: An experimental system is designed, constructed, and operated to make local measurements of heat transfer from constant-temperature surfaces in a linear turbine cascade. The system includes a number of embedded heaters and a control system to maintain the turbine blades and end walls in the cascade at a uniform temperature. A five-axis measurement system is used to determine temperature profiles normal to the pressure and suction sides of the blades and to the end wall. Extrapolating these measurements close to the surface, the local heat transfer is calculated using Fourier's law. The system has been tested in the laboratory, and results are shown for the temperature distributions above the surfaces and for the local variations in the Nusselt number on the different surfaces in the cascade. The system can also be used to study the heat and mass transfer analogy as considerable data are available for mass transfer results with similar geometries.

A Numerical Study of Energy Separation in a Jet Flow

Abstract: Redistribution of the total energy of a fluid in motion, which is called "energy separation," has been observed in various flow situations. Understanding the underlying mechanism of this interesting phenomenon has been limited due to lack of the temporal information on flow and temperature fields. In the present study, numerical simulation of a viscous circular jet was performed to provide detailed temporal information on pressure, vorticity, and total temperature fields. Nondimensionalized governing equations, including mass, momentum, and total energy conservation equations, were simultaneously solved by an equal-order linear finite element and fractional four-step method. The results show that the formation and transport of vortices induce a pressure fluctuation in the flow field. The fluid, which flows through the disturbed pressure field, exchanges pressure work with the surroundings, and gains or loses total energy. This work exchange leads to higher and lower total temperature regions than the surroundings. In addition to the presence and movement of the vortices, the results indicate that the vortex-pairing process significantly intensifies the pressure fluctuation and corresponding total temperature difference. This implies that the vortex-pairing process is a very important process in intensifying energy separation and might explain the enhancement of energy separation in a jet using acoustic excitation.

Flow visualisation and heat/mass transfer in a linear turbine cascade with tip clearance

Abstract: Flow visualisation and heat/mass transfer measurements in a linear turbine cascade with tip/casing clearances ranging from 0.60% to 6.90% of chord show the influence of blade tip geometry for a standard flat tip, a squealer tip and a geometry with a winglet on the pressure side and a squealer on the suction side of the blade. Oil-lampblack and oil-dot techniques show the surface flow on the blade endwall and tip while a laser light-sheet and a smoke wire indicate the three-dimensional flow in the tip clearance and blade passages. Local heat/mass transfer from the blade tips is measured using the naphthalene sublimation technique. Experiments with the standard flat tip blade clearly show that a separation bubble exists at the pressure side edge of the tip surface at all tip clearance levels. The effect of the tip leakage vortex on the secondary flows in the blade passage is also evident: with an increase of tip clearance, the horseshoe vortices disappear while the passage vortex is weakened and pus...