scholarly journals Simultaneous 1D hybrid fs/ps rotational CARS, phosphor thermometry, and CH* imaging to study transient near-wall heat transfer processes

2020 ◽  
Author(s):  
D. Escofet-Martin ◽  
A.O. Ojo ◽  
N.T. Mecker ◽  
M.A. Linne ◽  
B. Peterson
Keyword(s):  
Heat Transfer ◽  
Wall Heat Transfer ◽  
Transfer Processes ◽  
Phosphor Thermometry ◽  
Near Wall

Assessment of LES and RANS-LES Hybrid Models for Heat Transfer Predictions in Effusion Cooled Combustor Liners

2021 ◽  
Author(s):  
Vishwas Verma ◽  
Kiran Manoharan ◽  
Jaydeep Basani ◽  
Dustin Brandt
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Heat Flux ◽  
Hybrid Models ◽  
Surface Heat ◽  
Regions Of Interest ◽  
Wall Region ◽  
Wall Heat Transfer ◽  
Numerical Predictions ◽  
Near Wall

Abstract Accurate numerical predictions of surface heat flux on combustor liners in the presence of effusion cooling involve appropriate resolution of turbulent boundary layers and mixing of two different streams. Precise surface heat flux and wall temperature predictions are necessary for the optimal design of combustor liners to avoid burnout and damage to the combustor. Reynolds Average Navier Stokes (RANS) model has shown superior wall heat transfer predictions for steady flows; however, in combustor liners involving complex effusion jet mixing patterns, it fails. On the other hand, Large Eddy Simulation (LES) can capture to a good extent core flow mixing in such situations, but it requires very high-resolution near-wall meshes for accurate surface heat flux predictions. To overcome these issues, a hybrid model using RANS in the near-wall region and LES in the core region have been proposed for better wall heat transfer predictions. In this study, a numerical analysis is carried out to test the capability of RANS, LES and hybrid models (SBES, WMLES) for wall heat transfer predictions. The computational setup is a flat plate where freestream high-speed flow approaches a thirty-five degree inclined jet. The study is divided into two regions of interest, one before the jet freestream interaction and another post-interaction. We demonstrate with the SBES approach, surface heat flux can be predicted to much better agreement with the test data in both the regions of interest. Also, it is shown that such results can be obtained with much coarser mesh resolution, hence less computational cost, with hybrid models than pure LES.

Wall heat transfer of unsteady near-wall flow in internal combustion engines

2019 ◽  
Vol 20 (7) ◽  
pp. 817-833 ◽  
Author(s):  
Yuji Harada ◽  
Kenji Uchida ◽  
Tatsuya Tanaka ◽  
Kiyotaka Sato ◽  
Qianjin Zhu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Combustion Chamber ◽  
Wall Turbulence ◽  
Wall Heat Transfer ◽  
Proposed Model ◽  
Engine Combustion ◽  
Wall Flow ◽  
Near Wall Turbulence ◽  
Near Wall

Although the near-wall turbulence is not fully developed in the engine combustion chamber, wall heat transfer models based on flow characteristics in fully developed near-wall turbulence are typically employed in engine simulations to predict heat transfer. Only few studies reported the wall heat transfer mechanism in near-wall flow where the near-wall turbulence was not fully developed as expected in the engine combustion chamber. In this study, the velocity distribution and wall heat flux in such a near-wall flow were evaluated using a rapid compression and expansion machine. In addition to the experimental approach, a numerical simulation with highly resolved calculation mesh was applied in various flow fields expected in the engine combustion chamber. As a result, the turbulent Reynolds number that represents the relationship between turbulent production and dissipation varied in the wall boundary layer according to the near-wall flow condition. This behavior affects the wall heat transfer. Considering this finding, a new model was formulated by introducing a ratio of turbulent Reynolds number in an intended near-wall flow to that in fully developed near-wall turbulence. It was confirmed that the proposed model could improve the prediction accuracy of wall heat flux even in near-wall flow where the near-wall turbulence was not fully developed. By applying the proposed model in engine computational fluid dynamics, it was found that the proposed model could predict the wall heat flux in a homogeneous charge compression ignition gasoline engine with acceptable accuracy.

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