Unsteady airflow measurement results of the experiment by Lance were rediscovered by attempting different RANS turbulence models. And the differences between the model of low Reynold models, zero equation models and standard models are compared when natural convection is dominant. The simulation results show that the robustness of standard turbulence model is superior to the low Reynold models. For unsteady airflow simulation, when the fluid flow characteristics change into natural convection, according to the characters of the required sample point and switch to the corresponding suitable turbulence model, can increase the accuracy of unsteady simulation and reduces computation time.