Large-Eddy Simulation #141: Upwind Wall Experiment

LES RUN #125: Upwind Wall Experiment. This simulation was an experiment to determine if we could perturb the "prescribed inflow wall" randomly and in order to quickly generate large-eddies just downstream of it. To do this, the domain was 50 x 50 x 69 with dx=dy=dz=15. It was initialized horizontally homogeneous with a radiosonde sounding from the Sheboygan ISS during Lake-ICE on this morning of 13 Jan 98. Click here to see the NMSTASK file. This domain is 750 m (east-west) by 750 m (north-south) wide by 1.0 km tall and all over land with a roughness length of 10 cm. The flow is from the NW with a 400 m deep mixed layer. Radiation in the model is turned off and there is no surface heat flux. The west wall is a floating, prescribed inflow; the east wall is radiative outflow, and the north and south wall are cyclic.

Only the v-component of flow was randomly perturbed by + or - 0.5 m/s on each 1/2-s timestep along the west wall below 400 m. The results show the high-frequency noise quickly becoming correlated on the wall and the resulting roll-like structures immediately downwind of it. The movie is for 159 frames long (1-min and 39 s) and the time interval between frames is 0.5 s. One possible theory for coalesence of the eddies on the west wall is that the wall is a 2-D model. This prevents vortex tube stretching and larger scale structures grow on it.

UW Lidar // Oct 10, 1999 //

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