Physics Help Forum change in flow / velocity direction and the Reynolds number

 Oct 19th 2009, 01:37 PM #1 Junior Member   Join Date: Oct 2009 Posts: 1 change in flow / velocity direction and the Reynolds number Hi, I am interested in the relationship between changes in flow direction (and changes in flow velocity) and the Reynolds number. Reynolds number = (fluid density) * (velocity) * (tube length) / (viscosity) Reynolds number = (flow rate) * (tube length) / [(viscosity) * (cross-sectional area)] So, if the magnitude of the velocity vector remains the same, but the direction changes, how does this affect the Reynolds number? Would the velocity vector just be decomposed into the vertical (sine) and horizontal (cosine) components, and be analyzed independently? Or is there some way of taking the direction into account in the overall Reynolds equation? Also, is there a way of taking the angle of the change in direction into account when the tube curves in a single arc? Thanks!
 Oct 19th 2009, 10:12 PM #2 Physics Team   Join Date: Feb 2009 Posts: 1,425 I dont know much about this, but i feel that though we say velocity what is inferred is speed. Else, we will end up with a -ve reynolds number which is not consistent with the two definitions which you have provided unless we treat length also as a vector. Since it also deals with turbulence, i dont feel reversing the flow should change the onset of turbulence etc. We may also speak of the vel of light, but infer speed.