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

V.

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 [16].

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.

2. Conclusions

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.

References

Saren, V. E. (1994) Some Ways of Reducing Unsteady Blade Loads Due to Blade Row Hydrodynamic Interaction in Axial Flow Turbomachines, Second International Confer­ence EAHE, Pilsen, Czech Republic, pp.160 – 165.

Saren, V. E. (1995) Relative Position of Two Rows of an Axial Turbomachine and Ef­fects on the Aerodynamics in a Row Placed Between Them, Unsteady Aerodynamics and Aeroelasticity of Turbomachines, Elsevier, pp.421 – 425.

Huber F. W., Johnson P. D., Sharma O. P. et ol. (1995) Performance Improvement Through Indexing of Turbine Airfols. Part 1. Experimental Investigation, ASME Paper No. GT-27.

Griffin L. W. , Huber F. W. and Sharma O. P. (1995) Performance Improvement Through Indexing of Turbine Airfols. Part 2. Numerical Simulation, ASME Paper No. GT-28.

5 Dorney D. J. and Sharma O. P. (1996) A Study of Turbine Performance Increases Through Airfoil Clocking, AIAA Paper No.2816.

6 Hohn W. (2001) Numerical and Experimental Investigation of Unsteady Flow Interac­tion in a Low Pressure Multistage Turbine, XV Intern. Sump. On Airbreathing Engines, Sept. 2-7, Bangalore, India.

7 Saren V. E., Savin N. M., Dorney D. J., Zacharias R. M. (1997) Experimental and Numer­ical Investigatin of Unsteady Rotor-Stator Interaction on Axial Compressor Stage (with IGV) Performance, Unsteady Aerodynamics and Aeroelasticity of Turbomachines: 8 th Intern. Symp., Stockholm, Dordrecht et al.: Kluwer, P. 407-416.

8 Saren V. E., Savin N. M., Dorney D. J., Sondak D. L. (1998) Experimental and Numerical Investigatin of Airfoil Clocking and Inter-Blade-Row Gap Effects on Axial Compressor Performance, International Journal of Turbo and Jet Engines, 15, P. 235-252.

9 Savin N. M. and Saren V. E (2000) Hydrodynamic Interaction of the Blade Rows in the Stator-Rotor-Stator System of an Axial Turbomachine, Fluid Dynamics. Vol.35, _3, pp. 145-158.

10 Saren V. E. (1971) On Hydrodinamical Interaction of Cascades of Profiles in Potential Flow, Izv. gS of USSR, > GG, _4, pp.75-84.

11 Judin V. A. 1981 Calculation of Hydrodinamical Interaction of Cascades of Profiles with account of wakes, Aeroelasticity of Turbomachines Blades. Tras. of the СІАМ, _953, pp.52-66.

12 Saren V. E., Savin N. M., Krupa V. G. (2000) Experimental and Computional Research of a Flow Structure in a Stator-Rotor-Stator System of an Axial Compressor, The 9th Internaional Symposium on Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines (ISUAAAT), Lyon, France, September 4-8, pp.494 – 502.

13 Ivanov M.. Ja, Krupa V. G., Nigmatullin R. Z. (1989) Implicit High Accuracy S. K. Go­dunov Scheme for Integration of Navier-Stokes Equations, Journal of Calculating Math­ematic and Mathematical Physic, vol.29, No.6.

14 Saren V. E., Savin N. M., Krupa V. G., Petrovitchev A. M. (2001) Inflience of a Rotor – Stator Interaction on the Steady and Unsteady Characteristics of the Axial Compressor, Paper from the XV ISABE, Bangalore, India.

15 Saren V. E and Smirnov S. A. (2003) Unsteady Vortical Wakes behind Mutually Mov­ing Rows of Axial Turbomachine, Thermophysics and Aerodynamics, Vol.10, No.2.

16 Saren V. E, Smirnov S. A. (2003) Structure of Unsteady Vortical Wakes behind Blades of Mutually Moving Blade Rows of an Axial Turbomachine, The 10th Internaional Sym­posium on Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines (ISUAAAT), Durham, North Carolina, USA, Sept. 7-11.

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

аамтЫу 3

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.

Assembly 1

Assembly 2

Assembly 3

a) Measure of circumferential distortion of time-average flow

Assembly 1

Assembly 2

Assembly 3

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

Pressure surface

0. 2 0.4 0.6

Suction surface

Fig. 12.Static pressure pulsation on the S vanes, assembly 1

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