The flow through two ISA nozzles of area ratio zero and 0.4 was investigated to determine the nature of the flow and its variation with Reynolds number. Separation occurs within the nozzle of zero area ratio, the size of the bubble increasing with decreasing Reynolds number. The predicted discharge coefficient based on a simplified flow model agrees with experiment for large Reynolds numbers. Upstream influences affect the performance of the nozzle of area ratio 0.4. The flows through the two nozzles are not comparable, and potential-flow results cannot be used to explain flow in venturis and nozzles in pipes. The discharge-coefficient curve for area ratio 0.4 shows a distinct hump when based on the head differential measured as for venturis, but no hump when based on the head differential across the corner taps.

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