Model Experiments for the Design of a Sixty Inch Water Tunnel Part II

A recirculating type of water tunnel is designed to produce a steady stream of fluid having uniform velocity and pressure in the test section. However, the tendency of the recirculating system is to produce variations in velocity from point to point across a section of flow due to growth of the boundary layer. Superimposed on this variation of velocity in space is a variation of velocity in time caused by turbulence in the stream. The necessity of diverting the stream through 360 degrees and of adding energy by means of a rotary impeller introduces the possibility of superposition of steady large-scale turbulence on the stream, but correct design of elbows and pump can effectively eliminate this source of velocity variation.