TY - JOUR

T1 - Velocity and surface shear stress distributions behind a rough-to-smooth surface transition

T2 - A simple new model

AU - Chamorro, Leonardo P.

AU - Porté-Agel, Fernando

N1 - Funding Information:
Acknowledgements The authors gratefully acknowledge funding from NSF (grant EAR-0537856) and NASA (grant NNG06GE256). Computing resources were provided by the University of Minnesota Supercomputing Institute.

PY - 2009/1

Y1 - 2009/1

N2 - A simple new model is proposed to predict the distribution of wind velocity and surface shear stress downwind of a rough-to-smooth surface transition. The wind velocity is estimated as a weighted average between two limiting logarithmic profiles: the first log law, which is recovered above the internal boundary-layer height, corresponds to the upwind velocity profile; the second log law is adjusted to the downwind aerodynamic roughness and local surface shear stress, and it is recovered near the surface, in the equilibrium sublayer. The proposed non-linear form of the weighting factor is equal to ln(z/z01)/ ln(δi/z01), where z, δi and z01 are the elevation of the prediction location, the internal boundary-layer height at that downwind distance, and the upwind surface roughness, respectively. Unlike other simple analytical models, the new model does not rely on the assumption of a constant or linear distribution for the turbulent shear stress within the internal boundary layer. The performance of the new model is tested with wind-tunnel measurements and also with the field data of Bradley. Compared with other existing analytical models, the proposed model shows improved predictions of both surface shear stress and velocity distributions at different positions downwind of the transition.

AB - A simple new model is proposed to predict the distribution of wind velocity and surface shear stress downwind of a rough-to-smooth surface transition. The wind velocity is estimated as a weighted average between two limiting logarithmic profiles: the first log law, which is recovered above the internal boundary-layer height, corresponds to the upwind velocity profile; the second log law is adjusted to the downwind aerodynamic roughness and local surface shear stress, and it is recovered near the surface, in the equilibrium sublayer. The proposed non-linear form of the weighting factor is equal to ln(z/z01)/ ln(δi/z01), where z, δi and z01 are the elevation of the prediction location, the internal boundary-layer height at that downwind distance, and the upwind surface roughness, respectively. Unlike other simple analytical models, the new model does not rely on the assumption of a constant or linear distribution for the turbulent shear stress within the internal boundary layer. The performance of the new model is tested with wind-tunnel measurements and also with the field data of Bradley. Compared with other existing analytical models, the proposed model shows improved predictions of both surface shear stress and velocity distributions at different positions downwind of the transition.

KW - Atmospheric boundary layer

KW - Large-eddy simulation

KW - Roughness transition

KW - Surface shear stress model

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U2 - 10.1007/s10546-008-9330-x

DO - 10.1007/s10546-008-9330-x

M3 - Article

AN - SCOPUS:58049204300

SN - 0006-8314

VL - 130

SP - 29

EP - 41

JO - Boundary-Layer Meteorology

JF - Boundary-Layer Meteorology

IS - 1

ER -