Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session G20: Boundary Layers V: Compressible and Thermal |
Hide Abstracts |
Chair: Farzad Mashayek, University of Illinois at Chicago Room: 315 |
Monday, November 25, 2013 8:00AM - 8:13AM |
G20.00001: A quantitative theory for the mean velocity distribution of compressible ramp flow Wei-Tao Bi, Bin Wu, Hong-Yue Zou, Xin-Liang Li, Fazle Hussain, Zhen-Su She The flow induced by a compression ramp is of practical importance as a typical flow in the intake of a scramjet engine, yet no quantitative theory is available. This study proposes a quantitative theory for the mean velocity profile (MVP) of the compression ramp flow, based on a multi-layer description of turbulent boundary layers. Application of the theory on the direct numerical simulation (DNS) data shows that the mixing length function in the boundary layer after the reattachment point has a five-layer structure. A formula is given for the streamwise MVP, in very good agreement with the DNS data. Variation of the parameters in the formula with the spatial position is measured and discussed. These results further support the validity of the Structural Ensemble Dynamics approach to a wide class of wall-bounded flows, and a new modeling strategy for engineering computation of complex supersonic flows. [Preview Abstract] |
Monday, November 25, 2013 8:13AM - 8:26AM |
G20.00002: Turbulence Structure and Wall Signature in Hypersonic Boundary Layer Yin Chiu Kan, Pino Martin We will investigate the turbulence structure from direct numerical simulation (DNS) data of Mach 3 and Mach 7 turbulent boundary layers. In particular, we will use linear stochastic estimation to provide evidence of hairpin structures, examine the character of coherent structures statistically and instantaneously, as well as their wall signatures. In addition, we will use a spatio-temporal pattern finding process to track multiple packets evolutions concurrently. [Preview Abstract] |
Monday, November 25, 2013 8:26AM - 8:39AM |
G20.00003: Thermal boundary condition effects on compressible turbulent boundary layers Izaak Beekman, Pino Martin Numerous questions about the physics of compressible boundary layers, and their modeling remain open. While Morkovin's hypothesis has proven remarkably robust for zero pressure gradient, smooth wall, compressible, turbulent boundary layers, accounting correctly for thermal energy transport and its impact on the density and momentum fields remains challenging. We use spatially developing DNS data over strongly and weakly adiabatic walls at Mach 3 and Mach 7. The strongly adiabatic boundary condition further stresses common assumptions of weak direct compressibility and weak total temperature fluctuations. We observe non-trivial differences between the two cases. The simulations are performed at $Re_{\tau} \approx 500$ on very large domains in the streamwise and spanwise directions, approximately $50$ by $10 \delta_{inlet}$, with a rescaling method providing the inflow. We examine the effects of this boundary condition on common scaling laws, temperature-velocity relations, and suggest improvements, where possible. A dimensionless parameter is proposed, the ``fluctuation Nusselt number,'' to quantify the impact of the wall material for laboratory and engineering flows and relate it to these idealized, numerical boundary conditions. [Preview Abstract] |
Monday, November 25, 2013 8:39AM - 8:52AM |
G20.00004: Interaction of a Mach 2.25 turbulent boundary layer with a fluttering panel using direct numerical simulation Daniel Bodony, Christopher Ostoich, Philippe Geubelle The interaction between a thin metallic panel and a Mach 2.25 turbulent boundary layer is investigated using a direct numerical simulation approach for coupled fluid-structure problems. The solid solution uses a finite-strain, finite-deformation formulation, while the direct numerical simulation of the boundary layer uses a finite-difference compressible Navier-Stokes solver. The initially laminar boundary layer contains low amplitude unstable eigenmodes that grow in time and excite traveling bending waves in the panel. As the boundary layer transitions to a fully turbulent state, with $Re_\theta \approx 1200$, the panel's bending waves coalesce into a standing wave pattern exhibiting flutter with a final amplitude approximately 20 times the panel thickness. The corresponding panel deflection is roughly 25 wall units and reaches across the sonic line in the boundary layer profile. Once it reaches a limit cycle state, the panel/boundary layer system is examined in detail where it is found that turbulence statistics, especially the main Reynolds stress $-\langle u' v' \rangle$, appear to be modified by the presence of the compliant panel, the effect of which is forgotten within one integral length downstream of the panel. [Preview Abstract] |
Monday, November 25, 2013 8:52AM - 9:05AM |
G20.00005: Acoustic Radiation from High-Speed Turbulent Boundary Layers Lian Duan, Meelan Choudhari Direct numerical simulations (DNS) are used to examine the pressure fluctuations generated by a high-speed turbulent boundary layer with nominal freestream Mach number of 6 and Karman number of $Re_\tau \approx 464$. The emphasis is on comparing the primarily vortical pressure signal at the wall with the acoustic freestream signal under higher Mach number conditions. Moreover, the Mach-number dependence of pressure signals is investigated by comparing the current results with those of a supersonic boundary layer at Mach 2.5 and $Re_\tau \approx 510$. It is found that the freestream pressure intensity exhibits a strong Mach number dependence, irrespective of whether it is normalized by the mean wall shear stress or by the mean pressure. Spectral analysis shows that both the wall and freestream pressure fluctuations of the Mach 6 boundary layer have enhanced energy content at high frequencies. The computed Mach-number dependence of the acoustic field, including radiation intensity, directionality, and convection speed, is consistent with trends in measurements. The numerical database is used to understand the acoustic source mechanisms for both adiabatic and cold wall configurations. [Preview Abstract] |
Monday, November 25, 2013 9:05AM - 9:18AM |
G20.00006: Effects of radiation in turbulent boundary layers: Analysis of the mean temperature profile Ronan Vicquelin, Yufang Zhang, Olivier Gicquel, Jean Taine Direct numerical simulations fully coupled with radiative energy transfer in a turbulent channel flow have been performed for different temperature, optical thickness (pressure) and wall emissivity conditions. Radiation is treated from the CK approach and a Monte Carlo transfer method. Analysis of the results shows that, beside an additional wall radiative flux, the structure of the mean temperature field and the wall conductive flux often strongly differ from results without radiation. It is found that gas-gas and gas-wall radiation interactions generate antagonist effects. The first one tends to increase wall conductive flux while the second one to decrease it. Classical wall log-laws for temperature are therefore strongly modified by the global radiation effects. Many conditions encountered in applications are discussed. The observed modifications depend on all the set of conditions (temperature level, wall emissivity, pressure, Reynolds number), i.e. on the relative magnitudes of radiation gas-gas and gas-wall phenomena and of global radiation flux and conductive flux without radiation. [Preview Abstract] |
Monday, November 25, 2013 9:18AM - 9:31AM |
G20.00007: A wall model for LES accounting for radiation effects Ronan Vicquelin, Yufang Zhang, Olivier Gicquel, Jean Taine In several conditions, radiation can modify the temperature law in turbulent boundary layers. In order to predict such an effect and the corresponding change in conductive heat flux at the wall, a new wall model for large eddy simulation (LES) is proposed. The wall model describes the inner boundary layer which cannot be resolved by the LES. The radiative power source term is calculated from an analytical expression of the intensity field within the inner layer. In the outer layer, wall stress and conductive heat flux predicted by the wall model are fed back to the LES which is coupled to a reciprocal Monte-Carlo method to account for radiation. Several mixing-length models and turbulent Prandtl number formula are investigated. Then, the level of accuracy of the discretized radiation analytical model is investigated. Finally, fully coupled results are compared with Direct Numerical Simulation/Monte-Carlo results of turbulent channel flows at different Reynolds number, wall temperature and pressure conditions. The proposed wall model greatly improves the accuracy of the predicted temperature profiles and wall conductive heat fluxes compared to approaches without radiation accounted for in the inner layer. [Preview Abstract] |
Monday, November 25, 2013 9:31AM - 9:44AM |
G20.00008: Experimental investigation of thermally stable turbulent boundary layers Alexander J. Smits, Owen Williams, Tristen Hohman, Tyler van Buren Thermally stable turbulent boundary layers are prevalent in the polar regions and instrumental in determining surface heat fluxes. At present, theoretical treatments of such flows have been found to be inaccurate. Experiments were thus conducted to gain further insight into changes in turbulent structure and corresponding statistics under stable conditions. Isothermal and constant heat flux boundary conditions were investigated as well as smooth and rough surfaces. PIV was used to examine the velocity field, and a thermocouple rake was used to measure the mean temperature profile. Under particular investigation are (1) the existence of a critical Richardson number at which turbulence was strongly suppressed and whether this was influenced by the surface roughness condition, and (2) the effects of increased stratification on the hairpin vortex structure and its organization into packets. This work was made possible by support received through Princeton University's Grand Challenges-Energy program, supported by the Thomas and Stacey Siebel Foundation. [Preview Abstract] |
Monday, November 25, 2013 9:44AM - 9:57AM |
G20.00009: Turbulent thermal boundary layers subjected to severe acceleration Guillermo Araya, Luciano Castillo Favorable turbulent boundary layers are flows of great importance in industry. Particularly, understanding the mechanisms of quasi-laminarization by means of a very strong favorable streamwise pressure gradient is indeed crucial in drag reduction and energy management applications. Furthermore, due to the low Reynolds numbers involved in the quasi-laminarization process, abundant experimental investigation can be found in the literature for the past few decades. However, several grey zones still remain unsolved, principally associated with the difficulties that experiments encounter as the boundary layer becomes smaller. In addition, little attention has been paid to the heat transfer in a quasi-laminarization process. In this investigation, DNS of spatially-developing turbulent thermal boundary layers with prescribed very strong favorable pressure gradients (K=4x10-6) are performed. Realistic inflow conditions are prescribed based on the Dynamic Multi-scale Approach (DMA) [Araya et al. JFM, vol. 670, pp. 581-605, 2011]. In this sense the flow carries the footprint of turbulence, particularly in the streamwise component of the Reynolds stresses. [Preview Abstract] |
Monday, November 25, 2013 9:57AM - 10:10AM |
G20.00010: ABSTRACT WITHDRAWN |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700