Handbook of Turbomachinery Second Edition Revised - Ventech!

trailing edge. For convenience, we have positioned the first rake directly
behind one of the blade trailing edges, in this case the stator blade at top
dead center. Since we have chosen to use four rakes, the 32.78 blade spacing
is divided into four equal segments of 8.28 each. The second rake is then
positioned 8.28 past the trailing edge of blade number 4. Likewise, rake 3 is
positioned 16.48 past the trailing edge of blade number 7, with rake 4
positioned 24.68 past blade number 9. In this manner, each discrete part of
the nonuniform pressure flow field is measured. Should three rakes be used,
each rake would be indexed across a third of the blade passage, and so on
for any number of rakes in the measurement plane.
Similar care must be exercised in determining the radial position of the
sensors on the rake. Typical rakes will include between five and eight
individual pressure sensors per rake. Each sensor should be positioned at the
centroid of a constant-area ring. This is illustrated in Fig. 8. For this
example we have specified that a five-element rake be installed in the flow
field. In order to locate the position of the individual pressure sensors on the
rake the flow-path area is divided into five equal area rings as seen in Fig. 8.
The sensors are then located at the centroid of each equal-area ring. By
installing the sensors in this manner, each pressure tap ‘‘sees’’ equal-flow
areas. As a result, area-averaged data reduction can be accomplished by
Figure 8 Radial sensor distribution.
Copyright © 2003 Marcel Dekker, Inc.