A knowledge of the motion of a fluid as it undergoes a change in direction, and of the energy and pressure variations which accompany the directional diversion has many applications in engineering practice. The designing of duct and piping systems requires a knowledge of the pressure losses
incurred in the flow of a fluid around a bend. In large installations, it may be necessary to investigate means of reducing the pressure losses in elbows from the standpoint of power requirements. In installations such as wind tunnels and water tunnels constructed for aerodynamic and hydrodynamic research, the requirements for uniform velocity distribution and parallel
flow downstream from the bend are greater than pressure considerations, and a knowledge of the effects of guide vanes on flow around a corner is important. The efficiency of pumps, turbines, propellers, and fans is influenced by the relationships between curvature of the streamlines and the resulting pressures and velocities.