The tests covered measurements of the losses involved, of the pressure distributions round the bends, and shadowgraph observations of the flow patterns and shock waves in the bends. A range of bend radii as well as a range of aspect ratios of the cross-sectional shapes were covered. In each case the investigation was carried from low entry Mach numbers up to, and beyond, the point at which the pipe bend "choked". The main conclusions from these tests are:—n(1) For a given cross-sectional area and radius of the centre line of the bend, the most efficient shape for a rectangular cross-section at high entry Mach numbers is square.n(2) If the radius of such a bend is fairly gentle (e.g. 4-in. radius for a 2-in. square cross-section) the increase in bend losses with increase in entry Mach number is small up to the entry Mach number at which the bend "chokes".
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