516
14 Radial Compressors
14.2 Kinematic Parameters
We take a machine with radial end blades, as sketched in Fig. 14.3, as an example.
Departing from the results with this rotor shape, we determine the influence of the
backward sweep.
(14.1)
The degree of reaction is
,
−
=
−
2
1
02
01
h h
R h
h
We use here that the absolute inlet velocity lies in the meridional plane. We further
assume a constant meridional velocity component (v m ) within the rotor, so that
Thus
(14.2)
This relation is the same as the one derived for radial fans in Chap. 3. For radial end
blades:
0.9
y ≈ , thus R ≈ 0.55. Backward sweep of the blades decreases the work
coefficient and increases the degree of reaction.
The work coefficient is
.
D
y =
=
=
2 2u
2u
2
2
2
2
2
u v
v
W
u
u
u
with
and
/
/
.
2
2
02
01
2 2u
2
1
2 2u
2
1
h
h
u v
h h u v
(1 2v
1 2 v )
−
=
− =
−
−
with
.
/
,
/
/ .
2
2
2
2
2u
2m
2m
1
2
2
1
2 2u
2u
2u
2
v
v
v
v
v
h h u v
1 2 v
v
R 1 1 2
1 1 2
u
y
=
+
=
− =
−
= −
= −
Fig. 14.7 Diesel engine turbocharger with a radial compressor and an axial turbine
(courtesy KBB GmbH)