TRANSIENT NUMERICAL INVESTIGATON OF ROTOR CLOCKING IN 1.5 STAGE OF AN AXIAL TEST TURBINE WITH A BLADE-TO-VANE RATIO OF 1.5

摘要

In recent years clocking of stators and rotors in multi-stage axial compressors and turbines has become an important scope of scientific investigations aiming to reduce aerodynamic losses in these turbo machines and to affect the aerodynamic and thermal load, the unsteady forces and the flow conditions of following stages. Regarding the loss reduction, the target of clocking is to find a relative circumferential position of successive rows of vanes or blades, so that the low momentum region in the wake of the upstream airfoil impinges the leading edge of the vanes or blades of the following stage. Numerical investigations of clocking in a multi-stage arrangement require the transient calculation of the instationary flow field, so that the transient interaction between stationary and rotating airfoils is part of the calculations. In the present investigation, the transient version of the conjugate fluid flow and heat transfer solver CHTflow has been used. In this theoretical study the 1st rotor, 2nd vane and 2nd rotor of an axial test turbine are investigated. The cooling of 1st rotor and 2nd vane is taken into account by slot injections on the blade surface. The influence of the blade clocking has been investigated at four different circumferential positions of the 2nd rotor with respect to the 1st rotor. Despite of this change, all other geometric parameters and the boundary conditions are unchanged for the four configurations. The transient flow structures are analyzed by visualization of the entropy distribution and the helicity at different time steps in a midspan section. Thereby, it can be seen how the wakes of the rotor 1 are chopped by the successive stator and how they impinge on rotor 2. It is shown that the flow pattern in front of rotor 2 is not equivalent for the 3 blades in the calculated segment. Thus, the wakes of rotor 1 cannot continuously impinge the leading edges of rotor 2, so that there is no significant influence of the clocking position on the time averaged total efficiency of the stages to be found, although the time dependent values of the total efficiency show different behaviors for the analyzed clocking positions. Therefore it can be concluded that for the investigated configuration the effect of clocking on the efficiency is significantly reduced in case of a blade-to-vane ratio of 1.5, so that the distinction between advantageous and disadvantageous assembly positions is not important.