An efficient method for numerical modeling of thin air layer drag reduction on flat plate and prediction of flow instabilities

Abstract

Experimental researches on flat plates and ship models show that among many different methods of drag reduction, Air Layer Drag Reduction (ALDR) seems to be one of the most efficient methods. The physics behind different phenomena in this method is not completely clear and numerical modeling can help resolving this manner. There is a lack of exact numerical modeling of this flow because of its complexity and huge numerical cost due to the two-phase instabilities in case of DNS. Also common CFD simulations using URANS models involve significant errors. In this paper an efficient method for numerical modeling of ALDR is introduced which is a combination of linear stability and URANS modeling of the flowfield. The base flow is extracted from CFD which is used in linear stability analysis as the basis which results the frequency of the most unstable mode. The final CFD simulation is then carried out plus an additional perturbation term with that specific frequency. Results show that the implementation of this strategy significantly improves the results of the numerical modeling compared to the experimental results. The predicted flowfields also show some new aspects of physics of ALDR that had not been previously shown in experimental tests.