On the Validity of Scaling Transient Conjugate Heat Transfer Characteristics

Abstract

Accurate prediction of unsteady thermal loads is of paramount importance in several engineering disciplines and applications. Performing time-accurate unsteady conjugate heat transfer (CHT) simulations presents considerable challenges due to the markedly different time scales between the solid and fluid domains. Two methods have been recently proposed, aimed at addressing this issue: multiscale modeling (MSM) and equalized time-scales (ET). The former is based on the separation of the disparate short and long temporal scales of the solution and subsequent averaging of the flow/energy equations. In the latter, the equalization of the time scales is achieved through manipulation of the solid's thermal properties. Both methods are very appealing due to the possibility of being easily implemented on an existing solver. It becomes, thus, relevant to assess their performance and/or limitations. This paper work presents a comparative study of the two methods for the prediction of transient thermal load, first using a simplified case of a solid body with uniform temperature, then through the investigation of the prewarming phase of a steam turbine. Both methods are then compared against a reference baseline fully coupled (FC) CHT solution. The results show how the MSM allows greater accuracy and robustness with considerable saving in computational cost with respect to the baseline solution.

Study on Oxy-Methane Flame Stability in a Cylindrical Porous Medium Burner

“…Consequently, the time of the conjugate heat transfer is scaled, accompanied by scaling the product of density and heat capacity of the solid. The scaling will affect neither the Fourier nor the Biot number of the problem for transient simulations [41,42]. This method reduces the computational cost by more than 10 times.…”

Conjugate heat transfer: Some fundamentals and recent progress

“…It should be noted that there have been various efforts to explore potential options to circumvent or mitigate the challenge arising from the time-scale disparity. The possibility of moderating the time scale disparity with a modified solid material is explored by Diefenthal et al [25], and Łuczynski et al [26], which can lead to some considerable speedup of the transient CHT, but may also be associated to some non-negligible and non-physical fluctuations in the solid, (see Maffulli et al [27]). A hybrid approach is also employed to first use the modified material to provide more rapidly an approximate initial field.…”