International Journal of Heat and Fluid Flow

Passive scalar dynamics in a turbulent channel flow is studied with Direct Numerical Simulation at friction Reynolds number Re_tau=160 and Prandtl number Pr=1. The goal of the study is to assess the grid spacing requirement for an accurate estimation of various integral turbulent statistics, with a special focus on the scalar dissipation rate. The implemented spatial resolutions span from the resolution comparable to the similar Direct Numerical Simulations (DNS) studies in the past, to the very fine resolution implemented by Galantucci and Quadrio. All scalar fields are computed in parallel using a single velocity field resolved with the finest resolution, thus reducing the statistical variability. In addition, to confidently assess the grid spacing requirement, we also evaluate the statistical uncertainty. The standard resolution of the DNS studies (resolution used by Kim et al.) is usually sufficient for predictions of first and second-order integral turbulence scalar field statistics. Non-negligible corrections of the fourth-order integral statistics, especially the scalar dissipation variance profile, are observed with enhancement of the scalar resolution from the one used in the standard DNS studies to the resolution recommended by Vreman and Kuerten, which is roughly two times finer in each spatial direction. Further resolution enhancements produce only marginal differences.

We present an experimental benchmark database for the transitional cavity flow. The database is obtained by planar Particle Image Velocimetry measurements at the median plane of the cavity model, for Reynolds numbers between 6,300 and 19,000 based on the cavity height. A detailed uncertainty analysis of the experimental results is performed via the correlation statistics method for PIV uncertainty quantification and linear error propagation. The data contain the following variables:- x/H and y/H: locations (relative to the cavity H) in the streamwise and transverse directions, respectively-u, v: streamwise and transverse velocity components, respectively. These quantities are normalized with respect to the free-stream velocity.- TKE: turbulent kinetic energy. The TKE is normalized with respect to the square of the free-stream velocity.- Rxy: shear Reynolds stress. Rxy is normalized with respect to the square of the free-stream velocity.- Uncertainties of the above quantities (also normalized)- isValid: parameter that assumes the value 1 for valid vectors and 0 for invalid vectors.