Aerodynamics of a Trapped Vortex Combustor: A Comparative Assessment of RANS Based CFD Models

Hesham Khalil; Khalid Saqr; Yehia Eldrainy; Walid Abdelghaffar

Authors

Hesham Khalil Mechanical Engineering Department, Faculty of Engineering, Alexandria University, Alexandria, Egypt
Khalid Saqr Mechanical Engineering Department, Arab Academy for Science, Technology and Maritime Transport, Alexandria, Egypt
Yehia Eldrainy Mechanical Engineering Department, Faculty of Engineering, Alexandria University, Alexandria, Egypt
Walid Abdelghaffar Mechanical Engineering Department, Faculty of Engineering, Alexandria University, Alexandria, Egypt

Abstract

Trapped vortex combustion, TVC, has shown promising results in terms of wide stability range and low pressure drop. However, previous experimental and numerical studies, which were limited to DNS, have provided only global performance assessments. Also, high computational cost limitations of DNS motivated the need for evaluating other lower cost turbulent models. Consequently, three RANS turbulence models were assessed in the present work; RKE, SST-KW, and RSM, using 2D numerical computations. In addition, the effect of inlet flow Re on cavity flow physics and stability was explored for more detailed physical insight. Ansys Fluent 12 has been used in the computations with the steady state compressible pressure based solver. RSM was found to have the least prediction error percentage against experimental data with maximum value of 12.1% for all cases studied compared with 23.9 % demonstrated by the SST-KW which was the least accurate model. Increasing inlet flow Re by order of magnitude had no apparent effect on the main flow structure for the same cavity size. However, the 300 % Re increase from 9229 to 27687 has led to 10 times increase in turbulence levels and 3 times increase in recirculation zone strength which confirms the high stability range of these combustors. Finally, multiple vortex structures, either behind the forebody for smaller cavity sizes of H/Df < 0.6 or behind the afterbody for larger cavity sizes H/Df > 1, were noticed to be the main reason behind increased pressure drop from 0.8 to 1.1%. This study was conducted as a ground base for future TVC analysis.