<DOC>
<DOCNO>
212
</DOCNO>
<TITLE>
theory and tunnel tests of rotor blade for supersonic
turbines .
</TITLE>
<AUTHOR>
stratford,b.s. and sansome,g.e.
</AUTHOR>
<BIBLIO>
arc r + m 3275, 1960.
</BIBLIO>
<TEXT>
  in special circumstances where a large work
output is required from a turbine in a single stage
it is necessary to use high pressure ratios across the
nozzle blades, thus producing supersonic velocities at
inlet to the rotor .  as part of an investigation into such
turbines, several designs for the inter-blade passages of
the rotor have been tested in a two-dimensional tunnel,
a design theory being developed concurrently .
  the first design, featuring constant passage width
and curvature as in steam-turbine practice, but having
thin leading and trailing edges, was found to suffer from
focusing of the compression waves from the concave
surface, with consequent flow separation from the
opposite convex surface .  it gave a velocity coefficient of
measured at an inlet mach number of 1.90 and turning
angle of 140 deg .  the measured value compares favourably
with values from previous steam tests, where the
results have been in the range from 0.65 to 0.92 .
  from theoretical reasoning, and from additional test
observations, a subsequent passage was designed
having an inlet transition length of small curvature, leading
to a free-vortex passage of double the transition
curvature,. a small amount of contraction was incorporated .
schlieren photographs showed the flow in this
passage to be almost shock free .  a thin region of low-energy
air existed close to the convex surface, but liquidinjection
tests located only one small bubble of reversed flow .
pressure traverses at exit indicated a velocity
coefficient of 0.952, based on the area-mean total pressure .
when allowance is made for turning angle and
reynolds number this result appears to compare quite favourably
with previous work .
  it would seem that the optimum blade pitching in a turbine
would be about 20 to 30 per cent closer than in a
two-dimensional cascade .  however, the resultant pitching
tends to become very close, except at very large
turning angles, with the result that in some applications
difficulties could arise in the practical design and
manufacture .
  several uncertainties remain and the present design must be regarded
as still experimental .
</TEXT>
</DOC>
