Journal: International Journal of Heat and Fluid Flow

Abbreviation

Int. J. Heat Fluid Flow

Publisher

Elsevier

Journal Volumes

ISSN

0142-727X
1879-2278

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Publications1 - 10 of 29
  • The significant impacts of urban canyon configuration on non-isothermal flow, ventilation, and heat removal: Insights from PIV-LIF measurements
    Item type: Journal Article
    Xue, Yunpeng; Zhao, Yongling; Mei, Shuo-Jun; et al. (2024)
    International Journal of Heat and Fluid Flow
    Urban climate investigations often demand a comprehensive grasp of airflow dynamics within urban settings, notably in the context of street canyons. Despite the well-recognised disparities between two-dimensional (2D) street canyon and three-dimensional (3D) building arrays, only a limited studies have undertaken a thorough quantification of these variances across diverse domains, encompassing aspects such as ventilation, pollutant dispersion, and heat flux. In this study, we deploy a simultaneous Particle Image Velocimetry and Laser-Induced Fluorescence (PIV-LIF) technique to amass intricate flow and temperature data concerning isothermal and non-isothermal flows within both 2D street canyon and 3D building array models. Evident differences in flow characteristics and temperature distributions within and above the canyons have been observed. Notably, under non-isothermal conditions with a Richardson number of 1.12, the vertical ventilation rate and heat removal capacity along the centreline of a 2D street canyon have been determined to exceed those of 3D configuration by factors of up to 3 and 2.5 times, respectively.
  • Comparison of state-of-the-art droplet turbulence interaction models for jet engine combustor conditions
    Item type: Journal Article
    Klose, G.; Rembold, B.; Koch, R.; et al. (2001)
    International Journal of Heat and Fluid Flow
  • LES of transitional flows using the approximate deconvolution model
    Item type: Conference Paper
    Schlatter, Philipp; Stolz, Steffen; Kleiser, Leonhard (2004)
    International Journal of Heat and Fluid Flow
    Large-eddy simulations of transitional incompressible channel flow on rather coarse grids are performed. The standard approximate deconvolution model (ADM) as well as two modifications are compared to fully resolved direct numerical simulation (DNS) calculations. The results demonstrate that it is well possible to simulate transitional flows on the basis of ADM. During the initial phase of transition, the models remain inactive and do not disturb the flow development as long as it is still sufficiently resolved on the coarse large-eddy simulation (LES) grid. During the later stages of transition the model contributions provide necessary additional dissipation. Due to the dynamic determination of the model coefficient also employed for the standard ADM, no ad hoc constants or adjustments are needed. The results of the modified ADM show excellent agreement with DNS already on coarser meshes than the standard ADM, e.g. in the skin friction throughout the transitional phase, while preserving the accuracy for the fully developed turbulent channel flow. A grid-resolution study demonstrates convergence of LES to the DNS results. Results of the dynamic Smagorinsky model are included for comparison.
  • Large eddy simulation of multiple impinging jets in hexagonal configuration - Mean flow characteristics
    Item type: Journal Article
    Draksler, Martin; Ničeno, Bojan; Končar, Boštjan; et al. (2014)
    International Journal of Heat and Fluid Flow
  • Combining magnetic resonance measurements with numerical simulations - Extracting blood flow physiology information relevant to the investigation of intracranial aneurysms in the circle of Willis
    Item type: Conference Paper
    Zuleger, Dorothea I.; Poulikakos, Dimos; Valavanis, Anton; et al. (2010)
    International Journal of Heat and Fluid Flow
  • Numerical simulation of magnetohydrodynamic flow in a toroidal duct of square cross section
    Item type: Journal Article
    Vantieghem, S.; Knaepen, B. (2011)
    International Journal of Heat and Fluid Flow
  • Direct numerical simulation of a transitional rectangular jet
    Item type: Conference Paper
    Rembold, Benjamin; Adams, Nikolaus A.; Kleiser, Leonhard (2002)
    International Journal of Heat and Fluid Flow
  • Turbulent transport in an inclined jet in crossflow
    Item type: Journal Article
    Coletti, Filippo; Benson, Michael J.; Ling, Julia; et al. (2013)
    International Journal of Heat and Fluid Flow
    The present study experimentally investigates a turbulent jet in crossflow relevant to film cooling applications. The jet is inclined at 30°, and its mean velocity is the same as the crossflow. Magnetic resonance imaging is used to obtain the full three-dimensional velocity and concentration fields, whereas Reynolds stresses are obtained along selected planes by Particle Image Velocimetry. The critical role of the counter-rotating vortex pair in the mixing process is apparent from both velocity and concentration fields. The jet entrainment is not significantly higher than in an axisymmetric jet without crossflow, because the proximity of the wall inhibits the turbulent transport. Reynolds shear stresses correlate with velocity and concentration gradients, consistent with the fundamental assumptions of simple turbulence models. However the eddy viscosity is strongly anisotropic and non-homogeneous, being especially low along the leeward side of the jet close to injection. Turbulent diffusion acts to decouple mean velocity and concentration fields, as demonstrated by the drop in concentration flux within the streamtube issued from the hole. Volume-averaged turbulent diffusivity is calculated using a mass–flux balance across the streamtube emanating from the jet hole, and it is found to vary slowly in the streamwise direction. The data are compared with Reynolds-Averaged Navier–Stokes simulations with standard k − ε closure and an optimal turbulent Schmidt number. The computations underestimate the strength of the counter-rotating vortex pair, due to an overestimated eddy viscosity. On the other hand the entrainment is increasingly underpredicted downstream of injection. To capture the correct macroscopic trends, eddy viscosity and eddy diffusivity should vary spatially in different ways. Therefore a constant turbulent Schmidt number formulation is inadequate for this flow.
  • Spatio-temporal analysis of the turbulent flow in a ribbed channel
    Item type: Journal Article
    Coletti, Filippo; Cresci, Irene; Arts, Tony (2013)
    International Journal of Heat and Fluid Flow
    The turbulent flow in a channel with transverse ribs over one wall is studied experimentally. The height of the obstacles is about one tenth of the channel height, and the spacing is 10 times their height. The Reynolds number based on the channel hydraulic diameter and bulk flow velocity is 15,000. Velocity fields are obtained with high spatial and temporal resolution along the streamwise/wall-normal plane by means of time-resolved particle image velocimetry. Beside mean velocity and Reynolds stresses, the flow is investigated through two-point correlations, distributions of spanwise-swirling events, space–time velocity diagrams and power spectral density. Although the separated flow reattaches before the following obstacle is approached, a strong rib-to-rib interaction occurs. Spanwise vortices, 0.2 rib heights in size, are generated in the free shear layer, travel across the whole pitch, and may impact on the next rib. The large scale motions triggered by the separation grow in size until they reach the following obstacle. Flapping of the separated shear layer is observed at frequencies consistent with previous studies, causing the instantaneous reattachment point to fluctuate. The flapping initiates at the downstream edge of the obstacle tip, rather than at the upstream edge where the instantaneous separation occurs.
  • Subcritical spatial transition of swept Hiemenz flow
    Item type: Conference Paper
    Obrist, Dominik; Henniger, Rolf; Kleiser, Leonhard (2012)
    International Journal of Heat and Fluid Flow ~ 7th Symposium on Turbulence & Shear Flow Phenomena (TSFP7)
    It is known from experimental investigations that the leading-edge boundary layer of a swept wing exhibits transition to turbulence at subcritical Reynolds numbers, i.e. at Reynolds numbers which lie below the critical Reynolds number predicted by linear stability theory. In the present work, we investigate this subcritical transition process by direct numerical simulations of a swept Hiemenz flow in a spatial setting. The laminar base flow is perturbed upstream by a pair of stationary counter-rotating vortex-like disturbances. This perturbation generates high- and low-speed streaks by a non-modal growth mechanism. Further downstream, these streaky structures exhibit a strong instability to secondary perturbations which leads to a breakdown to turbulence. The observed transition mechanism has strong similarities to by-pass transition mechanisms found for two-dimensional boundary layers. It can be shown that transition strongly depends on the amplitude of the primary perturbation as well as on the frequency of the secondary perturbation.
Publications1 - 10 of 29