EFFECTS OF STATOR CLOCKINGIN SYSTEMOF ROWS STATOR-ROTOR-STATOROF THE SUBSONIC AXIAL COMPRESSOR
N. M. Savin, V. E. Saren
The Central Institute of Aviation Motors Aviamotornaya st. 2, Moscow, 111116, Russia *
Abstract Results of researches of blade rows unsteady interaction in the three-rows stage of the axial compressor are presented with the purpose of definition the gas – dynamical mechanism of clocking effects in system of rows stator-rotor-stator. Experiments were carried out on the large-dimensional low-speed compressor with measurements of stationary and unsteady fbw parameters. Mutual circumferential position of stator rows, axial gaps and numbers of blades in rows are varied. Results of measurements are compared to calculation of few parameters, received on the half-analytical theory of potential-vortical interaction of the airfoil cascades and by numerical simulation of averaged on Reynolds 2-D unsteady Navier-Stokes equations.
Keywords: Subsonic compressor, clocking effect
Perfection of modern axial turbomachines demands already at a design stage of the account of unsteady interaction of rotors and stators. As have shown researches of last years, this circumstance is connected not only to a traditional problem of resonant blade vibrations, but also with infhence of unsteadiness on the time-averaged gasdynamical characteristics of turbomachines. The level of periodic pressure pulsations in a flawing path of the axial turbomachine, designed on specified parameters, is determined by aerodynamic loading of the rows, axial gaps between them and the relation of numbers blades (or pitches) in rotors and stators.
*Work is executed at financial support of International scientific and technical centre (ISTC), the grant number 672.2.
K. C. Hall et al. (eds.),
Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines, 581-601. © 2006 Springer. Printed in the Netherlands.
One of displays of the mutual inflience of rows on their fbw is the effect of a mutual circumferential position of stators and (or) rotors (clocking effect). As have shown the first experiments at a transonic compressor stage with IGV [1,2] and on 4-stages turbine [3,4], at typical axial gaps between rows and equal (or multiple) numbers of vanes in stators their mutual circumferential position essentially infhences on a ft>w in rotor [1,2], and also on efficiency of stags [3,4].
According to the further experimental researches on turbines [5,6] change of efficiency at change of a mutual circumferential position of stators, having equal numbers of vanes, achieves 0,5 %. Detailed researches of atypical subsonic stage of the high pressure compressor [7,8] have shown, that appropriate change of efficiency achieves 1,5 %. Thus the level of stagnation pressure pulsation in an absolute ft>w changes twice. The done work changes a little bit, and change of efficiency is provided, mainly, due to change of useful work [7,8].
From theoretical methods of research of effect of mutual circumferential position of stators have received application a half-analytical method of potential – vortical interaction of mutually moving cascades [1,2,9-11] and a method of direct numerical integration of averaged on Reynolds 2-D unsteady Navier – Stokes equations, closed by this or that model of turbulence [3,4-8]. First of the specified methods is based on the most simple quasi-steady model of an incompressible flow and allows to describe qualitative features of investigated flow. This method theoretically predicted influence of a mutual circumferential position of stators on a flow of the located between them rotor before performance of the first experiments.
Numerical methods are widely used by various authors, however for a task unsteady interaction of rotors and stators demand significant computing resources. Besides it is necessary to recognize that for similar tasks there are not clear requirements to construction of calculation grid zones, and also inflience of used model of turbulence on accuracy of description of the unsteady vortical wakes dissipation. By that less, in overwhelming majority of the mentioned above works calculation and experimental data are compared.
Thus, available theoretical and experimental results allow to consider optimization of a mutual circumferential position of blade rows in an axial turbomachine as an effective control mean of unsteady interaction of rotors and stators for decrease of losses and pressure pulsations.
In given paper results of theoretical and the experimental researches are presented, executed on the large-dimensional compressor, which was specially created in CIAM for research of effects of unsteady interaction of blade rows of the axial compressor. The work was executed at financial support of the International Science and Technology Centre (ISTC), the Grant No.672-98. The first results, received on this compressor, were reported on previous ISUAAAT
Symposium in Lyons . As against the experiments executed earlier at modelling stages of the axial compressor [1,2,7,8], on the created compressor the complex research was carried out, including fbw laser anemometry between rows and digital processing of results of measurements of instant values of static pressure on the rotor case and on the stator vanes and also stagnation pressure between rows and behind a compressor. Researches are carried out at various axial gaps between rows and various numbers of blades in rows.
The basic attention in the paper is given to statement of the research problem, the developed measurement technique and the analysis of the results, allowing to reply on the questions, connected to use in the practical purposes of effect of a mutual circumferential position of stators in system of compressor rows stator-rotor-stator.