Handbook of Turbomachinery Second Edition Revised - Ventech!

for the ranges:
Re from 300 to 3610 4 ;
Zn=dh from 1:0 to4:8;
Xn=dh from 3:1 to12:5:
hav is based on an area one half-pitch on either side of any row in the crossflow
direction. Values of m and f 1 are each a function of both ðXn=dhÞ and
Re. The function f 2 is used to express the degradation effect of cross flow
caused by the accumulation of fluid from multiple rows of impingement jets,
it being unity when this effect is negligible.
In the absence of cross-flow effects, the simpler square array
correlation of Gardon and Cobonpue [85] is recommended:
Nud ¼ 0:286ðrVa Xn=mÞ 0:625
It should be noted that in-line hole rows appear to be superior in heattransfer
performance to staggered rows.
In the leading-edge region of an airfoil, where the external heat load
generally tends to be at its highest, the application of impingement cooling
becomes particularly valuable. Here, a row or array of impinging jets are
directed at the inside concave wall of a vane or blade leading edge from
either a tube insert (typical of a vane application) or from a cast-in or
machined feature (typical of a blade application). In these types of
applications, the impinged air is generally designed to flow in a chordwise
direction, either then exiting as a film or being utilized for further internal
cooling. Radial flow of the impinged air is largely avoided as this produces a
degradation of the system resulting from cross-flow effects.
The detailed impingement data of Chupp et al. [83] were obtained
with test models simulating turbine airfoil leading-edge configurations and
is therefore particularly useful in turbine airfoil leading-edge cooling
design applications. The experimental model used is typical of a vane
airfoil application with a single row of holes impinging into the leading
edge from a tube insert, with spent air flowing, unrestricted, in a chordwise
direction around the impingement tube. An equal flow split around each
side of the tube is assumed. The Chupp et al. correlations are
recommended for this geometry type. Heat-transfer coefficients were
correlated over the leading-edge radius region. Information on the
distribution of the heat-transfer coefficient was also obtained. The average
(over an arc of 1808 of the impinged target) and stagnation point (an arc
of approximately 258 of the impinged target) heat-transfer coefficients are
Copyright © 2003 Marcel Dekker, Inc.