example 10 on page 325 showed that the power produced by a wind turbine is proportional to the cube of the wind speed v. von karman found empirically that when a fluid flows turbulently over a surface, the speed of the fluid is often well approximated by v « 21/7, where z is the distance from the surface. wind turbine towers are often constructed at heights of 50 m, but surveys of wind speeds are usually conducted at heights of about 3 m. by what factor should the predicted wind power density be scaled up relative to the survey data?