Predicting the roughness length of turbulent flows over landscapes with multi-scale microtopography
Abstract
Abstract. The fully rough form of the law of the wall is commonly used to quantify velocity profiles and associated bed shear stresses in fluvial, aeolian, and coastal environments. A key parameter in this law is the roughness length, z0. Here we propose a predictive formula for z0 that uses the amplitude and slope of each wavelength of microtopography within a discrete-Fourier-transform-based approach. Computational fluid dynamics (CFD) modeling is used to quantify the effective z0 value of sinusoidal microtopography as a function of the amplitude and slope. The effective z0 value of landscapes with multi-scale roughness is then given by the sum of contributions from each Fourier mode of the microtopography. Predictions of the equation are tested against z0 values measured in ~105 wind velocity profiles from southwestern US playa surfaces. Our equation is capable of predicting z0 values to 50 % accuracy, on average, across a four order-of-magnitude range.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Oct 07, 2015
- Source ID
- 10.5194/esurfd-3-1107-2015
Entities
People
- J. D. Pelletier
- Jason P. Field
Organizations
- United States Army Research Laboratory