Numerical prediction of shrouded probe sampling performance and a study of subgrid scale models in large eddy simulation /
A numerical method was developed to predict the performance of a shrouded probe sampling at a zero yaw angle to a turbulent flow stream. The mean turbulent flow was calculated using the standard k - E turbulence closure model. The trajectories of particles in the flow field were simulated by solvi...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1996.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=743266361&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | A numerical method was developed to predict the performance of a shrouded probe sampling at a zero yaw angle to a turbulent flow stream. The mean turbulent flow was calculated using the standard k - E turbulence closure model. The trajectories of particles in the flow field were simulated by solving the corresponding Lagrangian equations of particle motion that includes such effects as inertia, drag, gravity, Saffinan force and turbulent diffusion. Three parameters describing the performance of a sampling probe: aspiration ratio, transmission ratio and wall loss, were calculated by tracking a large number of particles. A comparison was made between the numerically calculated and the experimentally measured values of wall loss and aspiration ratio. The agreement between the numerical prediction and tile experimental data was good. A predictive equation was formulated for the aspiration coefficient of shrouded probes. Use was made of a model for a single probe. A correlation function was proposed to take into account tile particle inertial enrichment in tile entrance region near the shroud walls. The correlation function was expressed as a function of Stokes number and velocity ratio for the shroud and determined using numerical results for the performance of shrouded probes. Tests of two first-order dynamic subgrid scale models and their base models - the Smagorinsky model and the kinetic energy model, were made using direct numerical simulation data at high Reynolds number (Taylor microscale Reynolds number RA =: 102 - 216) for homogeneous, isotropic forced flow and decaying flow and homogeneous rotating flow. The results show that the correlation coefficients between exact and modeled subgrid-scale stresses for both first-order models are fairly low and less than 30%. Based on the general relation between the subgrid-scale stress and the velocity gradient tensors, a second-order dynamic model was formulated, which includes the rotation rate tensor and the strain rate tensor. Numerical testing shows that the second-order dynamic model significantly improves the correlation coefficient. Subgrid nonlinear interaction and energy transfer were analyzed using direct numerical simulations of forced and decaying isotropic turbulence. Influence of cutoff wave number at different range of scale on the energetics and dynamics has been investigated. |
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| Item Description: | Vita. "Major Subject: Mechanical Engineering". |
| Physical Description: | xii, 101 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references. |