Numerical modelling of the turbulent flow developing within and over a 3-D building array, part I: A high-resolution Reynolds-averaged Navier-Stokes approach

A study of the neutrally-stratified flow within and over an array of three-dimensional buildings ( cubes) was undertaken using simple Reynolds-averaged Navier-Stokes (RANS) flow models. These models consist of a general solution of the ensemble-averaged, steady-state, three-dimensional Navier-Stokes equations, where the k-epsilon turbulence model (k is turbulence kinetic energy and epsilon is viscous dissipation rate) has been used to close the system of equations. Two turbulence closure models were tested, namely, the standard and Kato-Launder k-epsilon models. The latter model is a modified k-epsilon model designed specifically to overcome the stagnation point anomaly in flows past a bluff body where the standard k-epsilon model overpredicts the production of turbulence kinetic energy near the stagnation point. Results of a detailed comparison between a wind-tunnel experiment and the RANS flow model predictions are presented. More specifically, vertical profiles of the predicted mean streamwise velocity, mean vertical velocity, and turbulence kinetic energy at a number of streamwise locations that extend from the impingement zone upstream of the array, through the array interior, to the exit region downstream of the array are presented and compared to those measured in the wind-tunnel experiment. Generally, the numerical predictions show good agreement for the mean flow velocities. The turbulence kinetic energy was underestimated by the two different closure models. After validation, the results of the high-resolution RANS flow model predictions were used to diagnose the dispersive stress, within and above the building array. The importance of dispersive stresses, which arise from point-to-point variations in the mean flow field, relative to the spatially-averaged Reynolds stresses are assessed for the building array.