OF USE

Four necessary conditions for steady irrotational compressible flow-. through a straight cascade of blades are derived from the irrotationality condition and the conservation of mass and momentum. Expressions are obtained which measure the degree to which an approximate compressible-flow solution departs from these conditions. The expressions may be used as a measure not only of how well a given flow solution approxi-mates the flow of the usual polytropic gas, but also OY how well it approximates the flow of an arbitrary barotropic fluid..-As illustrations of’the use of the error expressions, they are applied to three basically different types of approximation to the flow of a pol.ytropicgas through a cascade of typical compressor blading; nemely, (1) the incompressible approximation, (2) the Prandtl-Glauert approximation, and (3) an approximation based on a linear relation between pressure and specific volume. The approximation based on the linear pressue-volume relation gave much the best agreement by satis