Direct numerical simulation of compressible turbulent flows close to their vapor-liquid critical point

Turbulent heat transfer characteristics of supercritical pressure fluids are quite different from those of subcritical pressure fluids. Experimental studies showed that heat transfer to supercritical fluids can exhibit dramatic heat transfer deterioration or enhancement. These phenomena lead to the presence of local minima/maxima in heat transfer coefficients or wall temperatures along a heated surface. In nuclear reactors the prediction of wall temperature is of paramount importance to improve the safety and performance of the nuclear power plants. We perform Direct Numerical Simulation (DNS) of a heated pipe flow to study in detail the occurring mechanisms leading to the heat transfer deterioration. The strong variation of the speed of sound (which exhibits a local minimum at the critical point) makes it necessary to account for acoustic wave propagations. Here we perform compressible DNS of wall bounded turbulent flows with supercritical fluids to study the occurring flow physics due to acoustic effects, and density and viscosity stratification.