A Direct Numerical Simulation of Flow Through a Low Pressure Turbine Stage

Abstract

The unsteady flow through a low-pressure turbine stage is computed via a direct numerical simulation using a high-order accurate upwind-biased finite-difference method. One objective of this investigation is to understand the interaction between the stator wake and the rotor; in particular flow separation and transition on the rotor pressure and suction surfaces. A second objective is to study the evolution of the stator wake as it convects through the rotor passage. The computed flow is explored with the aid of instantaneous velocity and vorticity contours and, timeand phase-averaged surface pressure. The distribution of the phaseaveraged turbulent kinetic energy and the production term in the b u d g e t of this energy are also used to understand the evolution of the stator wake in the rotor row. The rotor suction surface was found to be laminar (but disturbed) until about 60% chord. It then encounters periodic separation. The region of separation contains between two and three bands of separation. Interaction with the stator wakes results in a breakdown of some of these bands. Reattachment is achieved both via breakdown as well as convection off the rotor surface. Some suction surface flow separation is observed at most phases. The pressure side also exhibits periodic separation consisting of bands extending the width of the computational region in the spanwise direction; interaction with the stator wake results in their dissolution. The evolution of the stator wake in the rotor passage is similar to that observed in earlier studies. Bowing of the wake caused by varying velocity across the passage, the formation of an apex, an increase in turbulence intensity in the apex and other segments of the wake, observed elsewhere, are also seen here.