Two Delayed-Detached Eddy Simulation (DDES) models, and a Large-Eddy Simulation (LES) model are used to investigate the turbulent flows and mixed convection between a hot plate and a cold plate via the software FLU-ENT. The two DDES models include Production-limited DDES (PL-DDES) and Improved DDES (IDDES) models. The Wall-Adapting Local Eddy-Viscosity (WALE) model is the used LES model. The numerical computations are performed at Reynolds number Re-b = 4494 and different Richardson numbers Ri = 0.025, 0.048, 0.1. The comparing data is from the Direct Numerical Simulation (DNS) at Re-b = 4494 and Ri = 0.048. The comparison reveals that the Iwo DDES models have better performance in predicting time-averaged parameters than the WALE model in the aiding flow. The best predicted time-averaged results are obtained by the PL-DDES model in the opposing flow. Furthermore, the results of different Ri obtained by the PL-DDES model agree well with the DNS data. (C) 2019 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.