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 E30: Turbulence: Shear Layers I - Simulations |
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Chair: Cyrus Madnia, University at Buffalo - The State University of New York Room: 408 |
Sunday, November 24, 2013 4:45PM - 4:58PM |
E30.00001: Characteristics of the Turbulent/Non-Turbulent Interface in Compressible Shear Layers Navid S. Vaghefi, Cyrus K. Madnia Direct numerical simulation (DNS) of temporally evolving compressible turbulent shear layer at varying convective Mach numbers are used to assess the dynamics of the flow across the turbulent/non-turbulent (T/NT) interface separating the turbulent and the irrotational regions. This interface is detected by using a certain threshold for the vorticity norm. The conditional flow statistics based on the normal distance from the T/NT interface plane are compared for different convective Mach numbers. It is shown that the T/NT interface thickness for compressible cases examined is of order of the Taylor microscale, similar to the previous studies for incompressible flows with mean shear. Various terms in kinetic energy and vorticity transport equations are examined in order to determine the effects of compressibility on the transport mechanisms across the T/NT interface. [Preview Abstract] |
Sunday, November 24, 2013 4:58PM - 5:11PM |
E30.00002: Numerical study of shear layer instability in transverse jets Krishnan Mahesh, Prahladh Iyer Direct numerical simulations are performed to study the transition from absolute to convective instability for incompressible jets in crossflow using an unstructured finite volume solver. Flow conditions are based on experimental conditions of Megerian {\it et al.} (2007) for a flush injected jet. Results obtained from simulated jet velocity ratios of 2 and 4 are compared with experimental data (Getsinger {\it et al.} 2011 and Megerian {\it et al.} 2007) and show good agreement in instantaneous and time averaged flow characteristics as well as velocity spectra. Proper orthogonal decomposition (POD) and Koopman mode decomposition of the three-dimensional flow field is performed to identify the dominant flow features and their corresponding frequencies. [Preview Abstract] |
Sunday, November 24, 2013 5:11PM - 5:24PM |
E30.00003: The Turbulent/Non-Turbulent Interface in Non-Premixed Reacting Mixing Layers Reza Jahanbakhshi, Navid S. Vaghefi, Cyrus K. Madnia The results of the direct numerical simulation (DNS) of temporally evolving reacting mixing layer are used to study the flow characteristics across the turbulent/non-turbulent (T/NT) interface separating the turbulent and the irrotational regions. This interface is detected by using a certain threshold for the vorticity norm. The compressible form of the conservation equations for mass, momentum, and energy are solved. The hydrogen-air combustion is mimicked by a one-step global reaction. The infinitely fast chemistry approximation is used. The dynamic viscosity and heat capacities depend on local temperature and species mass fractions. The main objective of this work is to study the effects of heat release and flame location on kinematics and dynamics of the T/NT interface. [Preview Abstract] |
Sunday, November 24, 2013 5:24PM - 5:37PM |
E30.00004: Direct Numerical Simulation of a Temporal Mixing Layer and Detection of the Turbulent/Non-Turbulent Interface Fabian Hennig, Jonas Boschung, Michael Gauding, Norbert Peters The direct numerical simulation of a temporally evolving mixing layer is presented. Using the DNS data we compare two different approaches of detecting the so called turbulent/non-turbulent interface that is found between the fully turbulent and the irrotational outer flow. Standard and conditional statistics are evaluated and compared with literature results. [Preview Abstract] |
Sunday, November 24, 2013 5:37PM - 5:50PM |
E30.00005: Temporal behavior of strong shear layers in high Reynolds number turbulence Pradeep K. Jha, Takashi Ishihara High resolution direct numerical simulation (DNS) of isotropic turbulence with the Taylor micro-scale Reynolds number $R_\lambda=O(10^3)$ on $4096^3$ grid points was used to study the temporal behavior of strong shear layers in high Reynolds number turbulence. A time span of $10\tau_\eta=2.55\lambda/u'$ was simulated and analyzed, where $\tau_\eta$ is the Kolmogorov time-scale, $\lambda$ is the Taylor micro-scale and $u'$ is the $rms$ value of the velocity fluctuations. Detailed visualization showed excellent correspondence between regions with high enstrophy values and the existence of strong shear layers. Reasonably close-packed elongated strong vortices were found to exist in layer-like regions with thickness of the order of $\lambda$. A quantitative analysis of the DNS data showed that in these strong shear layers, strong vortices interact with the neighboring vortices and move drastically at a speed of the order of $u'$, maintaining an effectively constant distance between each other. The average size of these peak vortices also remains quasi-time-independent. The strong shear layers at the interfacial region remain sharp during the time evolution. These shear layers are significant intermittent structures of high Reynolds number turbulence. [Preview Abstract] |
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