Investigation of a Three-Stage Transonic Research Axial-Flow Compressor: Aerodynamic Design and Overall Performance Page: 34 of 59
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NACA RM LS5G27
action is similar to setting the tip section loading. Axial velocities
can then be determined from equation (A9) written between the tip and
any other radial station. The hub radius is then determined by solving
equation (A10) for rh. This method has the desirable feature that it
eliminates a trial and error solution of equation (Al0) for Vam and
also permits a tip section loading to be set directly.
The computational method used in the design of the compressor
herein reported was to compute velocities from the previously described
equations for a prescribed inner contour. An approximate method of
determining the Va,, in equation (A9) that would satisfy equation (A10)
was used. It was assumed that the mean radius conditions at blade row
inlet and exit stations represented average conditions. Downstream Va,m
and pm were computed from inlet and exit passage areas and the inlet
mean radius axial velocities and densities, that is, from
(PiVai)mA = (pVa)mA.
After the satisfaction of continuity (equation (A10)) by the above
method, the hub casing radii were arbitrarily reduced to account for
casing boundary-layer growth. This reduction in area is similar to
assuming boundary-layer blockage factors (K = Wd/Wideal). A tabulation
of the corresponding K factors is presented in table II. To determine
the effective boundary-layer blockage factors that resulted from the
actual hub radii, the assumed K factors, and the approximate method
of satisfying continuity that was used, Wideal was computed at each
axial station by a numerical integration of the calculated weight-flow
distributions. The hub radii used in these integrations were the actual
hub radii. A tabulation of the effective K's is presented in table II.
The fact that some of the K values are greater than 1.00 resulted
because the previously mentioned approximate method used to satisfy con-
tinuity yielded weight flows which were from 1 to 1.5 percent below the
design value. At the time this compressor was designed, very little
information was available regarding what values of K to use. Hence,
a redesign of the compressor to provide a smooth decrease in effective
K values from inlet to exit was considered to be unnecessary. It was
also felt that the increase in angles of attack which would result in
the third stage for K values above unity would not exceed the high
efficiency angle-of-attack range of that stage.33
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Savage, Melvyn & Beatty, Loren A. Investigation of a Three-Stage Transonic Research Axial-Flow Compressor: Aerodynamic Design and Overall Performance, report, October 27, 1955; (https://digital.library.unt.edu/ark:/67531/metadc61670/m1/34/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.