On influence of stators clocking on losses of total pressure in a compressor
The results of the presented above analysis of a fbw in system of rows IGV – R-S allow to make the conclusion, concerning observably in experiments [3-8] dependence of total pressure losses in a compressor stage from stators clocking
As follows from the experimental data received here, the parameter v does not influence on averaged on time aerodynamic characteristics of the R and S. At the same time the unsteady (periodic) part of velocity circulation on the R blades rather considerably may depend on a mutual circumferential position of stators. In this connection in works [5-8] the assumption was stated, that inflience v on losses of total pressure in a stage is caused by dissipation of the free vortexes, descending with R blades at change on them of velocity circulation. The results received in the given work directly allow to compare dependences from v intensity of free vortexes and losses of total pressure.
According to Thomson theorem running intensity of free vortexes 7 behind an airfoil at the moment of time t in a point of a wake with arc coordinate s, counted from a leading edge of an airfoil, is equal
where T is the period of a ft>w pulsation on the R blades.
The value є^) may be calculated according to experiment, which illustration is given on Fig.7. Function r(t) thus is determined as a result of the decision of the Cauchy-Lagrange equation concerning of velocity discontinuity on an airfoil pressure and suction sides at value of pressure difference known from experiment .
In turn the value of total pressure losses behind R is determined according to measurements by probes of the stagnation pressure, located behind the R and S, by calculation of value
APt = ((Pt2)t)y – ((Pt3)t)y
As shows experiment, as against time-averaged aerodynamic loadings on the R and S, values AP appear essentially dependent from v in particular for the assembly 1.
For the specified assembly on Fig. 14 dependences are presented
The received data show that in spite of the fact that r(t) is determined for peripheral section of the R blades, and value APt was measured on mean radius, character of dependences fi = fi(v) and A = A(v) are close. Areas v, appropriate to the lowered (increased) values of free vortexes intensity coincide with areas of the lowered (increased) values of total pressure losses behind the R.
It is necessary to notice that this result specifies also a source of the additional losses, caused a rotor-stator interaction in axial turbomachines.
The received results allow to formulate the following conclusions.
The presented experimental installation and the technique of data processing developed by authors allow to carry out complex researches of unsteady fbws, in particular, effects of a rotor-stator interaction in the subsonic axial compressors.
Researches of fbw properties show the following: – the rotor-stator interaction in a subsonic axial turbomachine at mean level of axial gaps (~ 15-25% of rotor blade pitch) does not infhence on time-averaged aerodynamic loadings on blades and structure of vortical wakes behind them;
– total pressure losses in a flow, caused a rotor-stator interaction, are bound up with additional losses owing to dissipation of free (periodic) vortexes in wakes behind blades.
Stator clocking effects in system of rows stator-rotor-stator of the axial compressor are bound up with influence of a mutual circumferential position of stators on unsteady aerodynamic characteristics of a rotor. The effects are most significant at equal number of stators vanes and essentially depend on axial gaps between rows. Stators clocking may serve as an effective practical control facility a level of the rotor-stator interaction in axial turbomachines.
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Figure 1. Compressor flow path and measurements
Fig.2 Radial distributions of stagnation pressure Pt and temperature Tt along flow path.
0 05 У* 1
0 0 5 Yigv 1 0 05 Yt
Fig. 4 Pitch-wise distributions of total pressure before R (left) and static pressure after R (right).
0 02 04 06 08 1 1 о 02 04 06 08 1 1
Fig. 7. Time variations of velocity circulation T.
Fia.8. Structure of vortical wakes behind R blade
0 0.2 0.4 0.6 0.8 1
Fig.9.Pitch-wise distributions of flow velocity behind R. Assembly 1.
a) Measure of circumferential distortion of time-average flow
b) Pitch-average measure of flow fluctuation
Assembly 1 Assembly 2 — Assembly 3
c) Measure of circumferential distortion of flow fluctuation
Fiq 10. Influence of mutual clocrinq positions of stators on relative flow velocity behind rotor.
Design operating mode: n=2000 rpm. Gcorr=30.8kg’s
0. 2 0.4 0.6
0. 2 0.4 0.6
Fig. 12.Static pressure pulsation on the S vanes, assembly 1