A prior simulation of a velocity field and a temperature field is carried out, and snapshot data of the velocity field and that of the temperature field are collected during the prior simulation. Then principal component analysis on the collected snapshot data obtains velocity-field and temperature field dimension transformation matrixes, on the based on which the analysis models of the velocity field and temperature field having respective first degrees of freedom are converted into reduced degree-of-freedom models. Consequently, a simulation of the velocity field and the temperature field is carried out using models having respective reduced degrees of freedom (i.e., second degrees of freedom).