Foreign Research Progress: Translations Issued by the N.A.C.A.

An investigation is made of two stapes of a multi‐stage turbo‐blower having a vanelcss diffuscr behind the impeller and guide vanes at the inlet to the next stage. The method employed was that of investigating the performance of the successive elements of the blower (the impeller, vaneless diffuser, etc.) whereby the kinematics of the flow through the blower could be followed and the pressure at the different points computed. The character of the flow and the physical significance of the loss coefficients could thereby be determined so as to secure the best agreement of the computed with the actual performance of the blower. Since the tests were carried out for various delivery volumes the dependence of the coefficients on a number of factors (angle of attack, velocities, etc.) could be obtained. The distribution of the losses that occur during the transformation of dynamic pressure at the impeller exit into static pressure could be found, and likewise the range within which the friction coefficient varies in the vaneless diffuser. With the aid of factors having a certain physical significance, the centrifugal blower could be computed on the basis of a more or less schematical consideration of the phenomena occurring during the air flow through it, and the use of arbitrary factors and recourse to the geometrical similitude law thus avoided. The present investigation largely summarizes all the previous work of the CAHI Blower Section on the different elements of a centrifugal blower. Some considerations on the analysis of model test data for application to full‐scale are presented in the appendix.