Lecture 39: Geomteric and dynamic similarities, examples
Example: A sphere of diameter 1 ft is to be dragged at a speed of 8.45 ft/s in seawater at . To predict the drag, we want to conduct an experiment on a 6” diameter sphere in air flowing past the model sphere. The drag on the model is to be kept at 6 lb-f. Determine the drag on the prototype. Answer: Ignoring any cavitation or compressibility effects, we have expression for drag:
Therefore, to predict the drag on the prototype one has to first match Reynolds number of two cases:
. To predict the drag, we want to conduct an experiment on a 6” diameter sphere in air flowing past the model sphere. The drag on the model is to be kept at 6 lb-f. Determine the drag on the prototype.
of two cases: 
and 
if 
