scholarly journals Effects of inlet velocity profiles for thermal stripping phenomena in T-junctions

2021 ◽  
Vol 2116 (1) ◽  
pp. 012026
Author(s):  
Lisa Lampunio ◽  
Yu Duan ◽  
Raad Issa ◽  
Matthew D. Eaton

Abstract This paper investigates the effects of different inlet velocities on thermal stripping phenomena within a T-junction. The computational flow domain is modelled using the Improved Delayed Detached Eddy Simulation (IDDES) turbulence model implemented within the commercial CFD code STAR-CCM+ 12.04. The computational model is validated against the OECD-NEA-Vattenfall T-junction Benchmark data. The influence of flat and fully developed inlet velocity profiles is then assessed. The results are in good agreement with the experimental data. The different inlet velocity profiles have a non-negligible effect on the mean wall temperature. The mean velocity shows lower sensitivity to changes in inlet velocity profiles, whose influence is confined mainly to the recirculation zone near the T-junction.

Author(s):  
Elizaveta Ivanova ◽  
Gregory M. Laskowski

This paper presents the results of a numerical study on the predictive capabilities of Large Eddy Simulation (LES) and hybrid RANS/LES methods for heat transfer, mean velocity, and turbulence in a fundamental trailing edge slot. The geometry represents a landless slot (two-dimensional wall jet) with adjustable slot lip thickness. The reference experimental data taken from the publications of Kacker and Whitelaw [1] [2] [3] [4] contains the adiabatic wall effectiveness together with the velocity and the Reynolds-stress profiles for various blowing ratios and slot lip thicknesses. The simulations were conducted at three different lip thickness and several blowing ratio values. The comparison with the experimental data shows a general advantage of LES and hybrid RANS/LES methods against unsteady RANS. The predictive capability of the tested LES models (dynamic ksgs-equation [5] and WALE [6]) was comparable. The Improved Delayed Detached Eddy Simulation (IDDES) hybrid method [7] also shows satisfactory agreement with the experimental data. In addition to the described baseline investigations, the influence of the inlet turbulence boundary conditions and their implication for the initial mixing layer and heat transfer development were studied for both LES and IDDES.


2019 ◽  
Vol 128 ◽  
pp. 05002
Author(s):  
Ali Cemal Benim ◽  
Michael Diederich ◽  
Ali Nahavandi

The present paper presents a detailed computational analysis of flow and dispersion in a generic isolated single–zone buildings. First, a grid generation strategy is discussed, that is inspired by a previous computational analysis and a grid independence study. Different turbulence models are appliedincluding two-equation turbulence models, the differential Reynolds Stress Model, Detached Eddy Simulation and Zonal Large Eddy Simulation. The mean velocity and concentration fields are calculated and compared with the measurements. A satisfactory agreement with the experiments is not observed by any of the modelling approaches, indicating the highly demanding flow and turbulence structure of the problem.


2018 ◽  
Vol 240 ◽  
pp. 04001
Author(s):  
Ali Cemal Benim ◽  
Michael Diederich ◽  
Fethi Gül

Aerodynamic behavior of a small wind turbine is analyzed, both experimentally and numerically. Mainly, an unsteady three-dimensional formulation is adopted, where the flow turbulence is modelled by an Improved Delayed Detached Eddy Simulation framework, using the four-equation transitional Shear Stress Transport model, as the turbulence model. A quite good agreement between the measurements and calculations is observed.


1967 ◽  
Vol 27 (2) ◽  
pp. 253-272 ◽  
Author(s):  
W. C. Reynolds ◽  
W. G. Tiederman

The Orr-Sommerfeld stability problem has been studied for velocity profiles appropriate to turbulent channel flow. The intent was to provide an evaluation of Malkus's theory that the flow assumes a state of maximum dissipation, subject to certain constraints, one of which is that the mean velocity profile is marginally stable. Dissipation rates and neutral stability curves were obtained for a representative two-parameter family of velocity profiles. Those in agreement with experimental profiles were found to be stable; the marginally stable profile of greatest dissipation was not in good agreement with experiments. An explanation for the apparent success of Malkus's theory is offered.


Author(s):  
N. Kharoua ◽  
L. Khezzar ◽  
Z. Nemouchi ◽  
M. AlShehhi

Large Eddy Simulation study of plane impinging jets with different inlet velocity profiles was conducted. The inlet velocity profile was forced at a frequency equal to 600Hz and amplitude equal to 30% of the mean inlet velocity. The Reynold number, based on the jet width W and the inlet velocity, is equal to 5600. The distance of the jet exit from the target wall was varied from 2W to 10W to cover different types of impinging jets with different flow structures. The time-averaged Nusselt Number Nu profiles, along the curved wall, are characterized by two peaks for the shortest distance 2W and only one peak, at the impingement region, for the largest distance 10W. The first peak, at the impingement region is investigated through profiles of the mean axial velocity, the rms axial velocity, the mean static pressure, and the mean static temperature plotted on the jet centerline. For the second peak of the Nu (2W case), the turbulence level and the thickness of the highly turbulent layer near the curved wall were depicted on curved lines parallel and very close to the target wall. Forcing the considered jets at 600Hz was found to reduce the Nu while a fully developed inlet velocity profile causes an important increase of the Nu at the impingement region compared with flat inlet velocity profiles.


2007 ◽  
Vol 129 (11) ◽  
pp. 1372-1383 ◽  
Author(s):  
Kyoungsik Chang ◽  
George Constantinescu ◽  
Seung-O Park

The three-dimensional (3D) incompressible flow past an open cavity in a channel is predicted using the Spalart–Almaras (SA) and the shear-stress-transport model (SST) based versions of detached eddy simulation (DES). The flow upstream of the cavity is fully turbulent. In the baseline case the length to depth (L∕D) ratio of the cavity is 2 and the Reynolds number ReD=3360. Unsteady RANS (URANS) is performed to better estimate the performance of DES using the same code and meshes employed in DES. The capabilities of DES and URANS to predict the mean flow, velocity spectra, Reynolds stresses, and the temporal decay of the mass of a passive contaminant introduced instantaneously inside the cavity are assessed based on comparisons with results from a well resolved large eddy simulation (LES) simulation of the same flow conducted on a very fine mesh and with experimental data. It is found that the SA-DES simulation with turbulent fluctuations at the inlet gives the best overall predictions for the flow statistics and mass exchange coefficient characterizing the decay of scalar mass inside the cavity. The presence of inflow fluctuations in DES is found to break the large coherence of the vortices shed in the separated shear layer that are present in the simulations with steady inflow conditions and to generate a wider range of 3D eddies inside the cavity, similar to LES. The predictions of the mean velocity field from URANS and DES are similar. However, URANS predictions show poorer agreement with LES and experiment compared to DES for the turbulence quantities. Additionally, simulations with a higher Reynolds number (ReD=33,600) and with a larger length to depth ratio (L∕D=4) are conducted to study the changes in the flow and shear-layer characteristics, and their influence on the ejection of the passive contaminant from the cavity.


2017 ◽  
Vol 34 (2) ◽  
pp. 123-134 ◽  
Author(s):  
L. Zhang ◽  
J. Li ◽  
Y. F. Mou ◽  
H. Zhang ◽  
W. B. Shi ◽  
...  

AbstractAccurate prediction of the flow around multi-element airfoil is a prerequisite for improving aerodynamic performance, but its complex flow features impose high demands on turbulence modeling. In this work, delayed detached-eddy-simulation (DDES) and zonal detached-eddy-simulation (ZDES) was applied to simulate the flow past a three-element airfoil. To investigate the effects of numerical dissipation of spatial schemes, the third-order MUSCL and the fifth-order interpolation based on modified Roe scheme were implemented. From the comparisons between the calculations and the available experimental result, third-order MUSCL-Roe can provide satisfactory mean velocity profiles, but the excessive dissipation suppresses the velocity fluctuations level and eliminates the small-scale structures; DDES cannot reproduce the separation near the trailing edge of the flap which lead to the discrepancy in mean pressure coefficients, while ZDES result has better tally with the experiment.


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