The Effect of Reynolds Number on the Passive Scalar Field in the Turbulent Wake of a Circular Cylinder

In this paper we investigate by experiments the effect of Reynolds number on a passive scalar (temperature) field in the turbulent wake of a slightly heated circular cylinder. The Reynolds number defined by Re≡U _∞ d/ν (see Nomenclature) is varied from Re= 1200 to Re= 8600. Temperature differential above ambient is chosen to be the passive scalar quantity. Present measurements are conducted using a cold wire (0.63 μm) probe. Results obtained suggest that Reynolds number in general has significant influence on the scalar mixing characteristics in the entire wake flow. Specifically, as Re increases, the mean scalar spreads out more rapidly, the scalar fluctuation intensity increases; however, its variance decays at a lower rate with downstream distance. It is also found that an increase of Re accelerates the streamwise evolution of the scalar probability density function from highly non-Gaussianity to near Gaussianity along the wake centreline. This reflects the reduction in length of the Karman-vortex street caused by an increase of Re.