Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session H22: Turbulence Mixing II: Heat Transport |
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Chair: Stefano Leonardi, University of Puerto Rico Room: 30C |
Monday, November 19, 2012 10:30AM - 10:43AM |
H22.00001: Direct Numerical Simulations (DNS) of the thermal field in a turbulent channel flow with spanwise sinusoidal blowing/suction Can Liu, Guillermo Araya, Luciano Castillo, Stefano Leonardi Direct Numerical Simulations (DNS) of an incompressible turbulent channel flow with given local perturbations at the walls are performed. Steady blowing and suction are applied at both walls by means of five spanwise holes. The sinusoidal perturbing velocity is considered at several amplitudes (0.025, 0.1 and 0.2 based on the centerline velocity) as well as at two different angles (30 and 40 degrees with respect to the flow direction) in order to explore its effects on the adiabatic efficiency. The Reynolds number of the unperturbed case is Re = 394 and the molecular Prandtl number is Pr = 0.71. Isoflux conditions are assumed for the lower and the upper walls. Furthermore, turbulence statistics, energy budgets and energy spectra are going to be examined for the velocity and thermal fields. [Preview Abstract] |
Monday, November 19, 2012 10:43AM - 10:56AM |
H22.00002: ABSTRACT WITHDRAWN |
Monday, November 19, 2012 10:56AM - 11:09AM |
H22.00003: Devising scaling parameters for wall bounded turbulent thermal transport Chiranth Srinivasan, Dimitrios Papavassiliou Scaling of turbulent heat transfer from a wall with the friction temperature does not work well for all turbulence quantities and for all Prandtl number (Pr) fluids. The lack of a comprehensive database covering heat transfer statistics for a wide range of Pr and Reynolds numbers (Re) has hindered recent investigations to obtain more appropriate scaling parameters. This study uses turbulent transport statistics from our extensive database to propose a new scaling framework for turbulent transport. The database is obtained by using DNS in conjunction with Lagrangian tracking of heat markers to generate heat transfer statistics in a turbulent channel flow. The simulated cases involve applying uniform heat flux on one wall while maintaining the other wall adiabatic, or applying uniform heat flux on both walls. The channel half-height is equal to 150 and 300 in viscous wall units and the Pr varies between 0.1 and 50,000. It is found that the peak value of the turbulent heat flux appears to be a parameter that can be used to asymptotically collapse the mean and the fluctuating scalar profiles to corresponding single profiles for different Re and Pr, thus, establishing the peak normal turbulent heat flux as an important scaling parameter. [Preview Abstract] |
Monday, November 19, 2012 11:09AM - 11:22AM |
H22.00004: Preliminary Results in an Ablation Wind Tunnel Michael Allard, Christopher White, Yves Dubief We have constructed a small-scale boundary layer wind tunnel to study rapid turbulent ablation of a surface subjected to a heated flow to better understand the complex coupling between an erodible surface and an eroding agent. The test section of the tunnel is 303mm $\times$ 141mm cross-section and 2.75m in length. The turbulence management section contains a 4:1 contraction, honeycomb, and 4 screens of decreasing mesh size. A 3/4HP fan is used to establish air flow in the tunnel and a frequency controller is used to control and maintain constant flow speed, which can be varied between 0.1 to 18m/s. A bank of electric heaters and a proportional integral derivative (PID) controller is used to maintain constant inlet air temperature. Characterization of the flow field over a non-ablative surface is reported, and qualitative observations of vortex induced erosion patterns on an ablative wall are presented. [Preview Abstract] |
Monday, November 19, 2012 11:22AM - 11:35AM |
H22.00005: A POD analysis of rough surface pressure and temperature fluctuations in a spatially developing turbulent boundary layer Luciano Castillo, Jensen Newman, Ronald Adrian, Yi Chen It is desired to gain a better understanding of how the presence of surface roughness in a turbulent boundary layer affects phenomena such as heat transfer and aeroacoustic noise generation. With this in mind, it is expected that by examining the most dominant features of these scalar fields in flows with and without surface roughness progress could be made towards this end. Hence, a Proper Orthogonal Decomposition (POD) was performed on the surface temperature and pressure fluctuations of a DNS simulation with a smooth wall, and one with a rough wall. The rough topography corresponded to an actual rough topography measured from 24 grit sand paper. Reynolds numbers based on momentum thickness ranges for the simulations were 1922-2269 for the smooth and 2077-2439 for the rough. The low order POD modes correspond to the dominant features of interest in these scalar fields. By comparing the smooth and rough cases, important qualitative differences in the dominant features were observed. [Preview Abstract] |
Monday, November 19, 2012 11:35AM - 11:48AM |
H22.00006: Effect of surface heating on the drag crisis of sphere Masaya Muto, Hiroaki Watanabe, Makoto Tsubokura The characteristics of flow past a heated sphere are investigated at around critical Reynolds number in conditions using three-dimensional numerical simulation in which temperature dependence of fluid properties such as density and viscosity is exactly considered. Boussinesq approximation is no longer applicable due to large temperature difference adopted in this study. And the order of the buoyancy effect becomes relatively small compared to inertia effect in present Reynolds number region. The result shows that drag coefficient of the heated sphere in drag crisis region becomes larger than that of the unheated case and it increases up to the coefficient found in subcritical region. This is because the temperature difference between the sphere and ambient fluid strongly affects the flow separation points, resulting in small recovery of the pressure in the wake and reduction of the temporal fluctuation of the lift force acting on the sphere. These effects are considered to attribute to the temperature dependence of fluid properties in the vicinity of the sphere and effect on the transient of the boundary surface. [Preview Abstract] |
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