TRANSIENT ANALYSIS OF A TRANSONIC COMPRESSOR ROTOR WITH AEROELASTIC EFFECTS

High fidelity aeroelastic analysis of gas turbine blading is becoming increasingly common. It is used in vibration analysis and prevention, to increase accuracy of off-design flow analysis and performance prediction, and in damage investigation. Here, an aeroelastic analysis is performed of the transient response of a transonic rotor to a change in operating point. An existing aeroelastic method is used that was originally developed and validated for aircraft applications. The method consists of a time-accurate CFD-method coupled with a modal approach for geometry deformation. The validity of the aeroelastic method is confirmed using the standard aeroelastic test case STCF4. Next, the transient behavior of a transonic rotor due to a change in operating point is investigated. Two scenarios are analyzed: from design point to near stall, and from design point to near choke conditions. These scenarios were analyzed using time-accurate U-RANS calculations with rigid and deformable blading, using six vibration modes to describe the blade deformation in the latter case. In the case of a rigid blade, the shock quickly moves from the original position to the position associated with the new operating point. The duration of this process is approximately one rotor revolution, but a small oscillatory movement remains after three rotor revolutions. With deformable blading, the changing pressure distribution deforms the blade shape during the transient process. The geometric displacement is very small, on the order of 10 mu m, and has only a minor effect on the observed shock movement. The final extent of deformation is reached within 0.5 rotor revolutions, but the blade continues to vibrate after three rotor revolutions. The oscillatory displacements of both the shock and the blade are very small for this particular geometry. For different configurations, the blade deformations might be large enough to influence the shock motion, possibly giving rise to noise and fatigue problems.