Comparison techniques for small sonic nozzles

Two techniques are described that allow small sonic nozzles to be compared. The first allows one nozzle to be compared easily and accurately with another at the same inlet conditions. The second allows a nozzle with a particular inlet pressure to be compared with the same nozzle at a different inlet pressure. A description of the calibration of two sets Of sonic nozzles is given in some detail. The first is a set of nominally equal nozzles and the second is a set of nozzles of varying sizes used to produce a range of closely spaced flows for the calibration of flow meters. The redundant measurement scheme with its design and variance-covariance matrices is described, and some results of actual measurements given. Results of the measurement of the change of discharge coefficients with Reynolds number for nozzles of throat diameters 0.7, 1.0 and 1.4 mm are given and compared with previous work. (C) 1997 Elsevier Science Ltd.