Turbulent Fluid Flow over Aerodynamically Rough Surfaces Using Direct Numerical Simulations

Abstract

Incompressible turbulent fluid flow in aerodynamically rough channels is investigated using direct numerical simulations. A comprehensive database of simulation data for rough surfaces with different topographical properties has been developed for 17 industrially relevant rough surface samples. It includes numerous commonly-seen industrial rough surfaces such as concrete, graphite, carbon-carbon composite and ground, shotblasted and spark-eroded steel. Other surfaces such as cast, filed and gritblasted steel are also studied, along with replicas of ship propeller surfaces eroded by periods of service. The Reynolds number considered is $Re_{\tau } = 180$, for which the flow is in the transitionally rough regime. A study with variable $\delta /S_q$ ratio, while keeping $S_q^+$ constant, where $S_q$ is the root mean squared roughness height, is conducted for one of the samples with the mean profiles showing convergence for $\delta /S_q >\approx 25$. A Reynolds number dependence study is conducted for two of the samples with $Re_{\tau }$ up to 720 showing a more complete range up to the fully rough flow regime, allowing the equivalent sandgrain roughness height, $k_s$, to be computed. A correlation based on the frontal and wetted roughness area is found to be superior to the surface skewness in predicting $\varDelta {U^+}$ based on the topographic surface parameters.