Scaling of Turbulent Mixed Convection under High Pressure

Abstract

Measurement of turbulent mixed convection at reduced model size by aerodynamic scaling is a promising approach to simplify the investigation of many technical configurations and offers the potential to make large scale flows accessible on a laboratory scale. First results of an experimental study of turbulent mixed convection in a generic convection cell at ambient and high pressure are reported. The aim of these measurements is to prove the possibility of scaling mixed convection by varying fluid pressure and inflow velocity. We present and discuss results for mixed and forced convection obtained with air as working fluid (Pr 0.7) at ambient pressure for Gr = 3.52 · 10⁶, Re = 1.1 · 10³ and thus Ar = 1.81 and at 10 bar with Gr = 3.51 · 10⁸, Re = 1.1·10⁴ and thus Ar = 1.83. The scaling theory, which allows to scale the cell, is presented as well as the PIV set up used for measurement at high pressure conditions in the High Pressure Wind Tunnel of Göttingen (HDG) and the convection cell. At elevated fluid pressure a significant increase of the velocity fluctuations was observed. Furthermore for mixed convection a transition of a stable 2D flow into an instationary 3D flow has been found.