Fluctuating Pressure and Velocity Fields in the Near Field of a Round Jet (Turbulent, Shear Layer, Triple-Wire, Self-Preserving, Hot)
Chang, Paul Hsin-Pei
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https://hdl.handle.net/2142/70130
Description
Title
Fluctuating Pressure and Velocity Fields in the Near Field of a Round Jet (Turbulent, Shear Layer, Triple-Wire, Self-Preserving, Hot)
Author(s)
Chang, Paul Hsin-Pei
Issue Date
1985
Department of Study
Mechanical Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Abstract
A new analysis algorithm for analyzing signals of a triple-wire anemometer probe is presented which describes the performance of the hot-wire probe and shows the ambiguity in interpretation of the three effective cooling velocities for a range of flow vector directions. Jorgensen's (1971) cooling law for cylinders inclined to the flow vector is adopted. Inverted velocity vectors are multiple but a uniqueness domain, within which the vector coinciding with the true velocity vector can be singled out, is defined. Samples of linearized voltages were taken in the turbulent shear layer of a 6.35 cm diameter jet and analyzed by the algorithm. The results appear to support the methodology of the algorithm. The mechanisms that cause some of the samples to reside outside the realizable domain are discussed.
A dynamic test in terms of pressure-velocity correlation in an unsteady irrotational flow was performed for the bleed-type pressure transducer. Pressure-velocity correlations calculated from the unsteady Bernoulli equation agree closely with direct measurements with the pressure transducer. The consistency of the pressure probe measurement and the correlation inferred from the Bernoulli equation show that the pressure transducer has properly dynamic response.
The triple-wire probe together with the pressure transducer were used to investigate the shear layer of a round jet. Comparison between the triple-wire and a regular X-wire data shows good agreement in low turbulence level regions. Experimental results support the existence of an apparent self-preserving zone between 3 < X/D < 5. Single-point pressure-velocity correlations spanning the shear layer qualitatively support the generation of pressure fluctuation inferred from the Poisson equation except the localization instead of long range effect. P-u(,i) cross spectra show the power law behavior between K(,1)('-8/3) and k(,1)('-2), but closer to K(,1)('-8/3) power law. Data support the simple gradient transport model including the transport of pressure energy.
Two-point pressure-velocity spatial-time correlations were measured in detail with stationary velocity and moving pressure probes. Conditional average and linear estimation results agree very well. Conditional pressure fields show the vortex structure with a wavelength about 1.1 nozzle diameters.
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