A common design goal for aircraft engines is to minimize size and weight while improving overall efficiency. One method to accomplish this reduction is to decrease the axial gaps between airfoil rows. However, for small axial gaps, strong viscous and inviscid interactions can occur between the airfoil rows and affect the efficiency of the turbine or compressor. Inviscid interactions occur as rotor or stator airfoils pass through the potential fields of adjacent airfoils. Viscous interactions are extremely complex because of the endwall boundary layer growth, passage vortical flows, wakes and tip leakage flows being generated within a turbomachine. These viscous flow features convect with the fluid to interact with other flow features as well as with downstream airfoils to form an extremely complicated aerodynamic environment within a turbomachine. In multistage turbomachines, wakes and other viscous structures can be convected many airfoil chords, causing the flow conditions in the downstream stages of the turbomachine to be much more complex than the conditions upstream.
The time-varying, multi-element geometries found in axial turbomachines make both experimental and computational investigations of these flows extremely challenging. Most computational investigations have focused on investigating the steady flow within a cascade to reduce the computational time and to eliminate problems associated with modeling both stationary and rotating components. In addition, many different time-averaged methods have also been used to determine the flow in multistage turbomachines. Among these approaches are Huber and Ni and Adamczyk, et al. who circumferentially average conditions on interface planes between rotor and stator airfoils to determine the time-averaged flow in multistage turbines. Adamczyk has used the passage-averaged method to evaluate some fluctuating terms due to deterministic stresses induced by airfoil wakes.
An approach developed by Rai and Madavan et al. has been used to compute the three-dimensional unsteady flow in a single-stage turbine. These efforts led to the development of the three-dimensional single-stage turbomachinery code, ROTOR-4. A concurrent effort by Gundy-Burlet et al. has led to the development of the two-dimensional STAGE-2 code which computes unsteady flows in multistage turbomachines. These studies used systems of patched and overlaid grids to compute rotor/stator interaction in axial-flow turbomachines.
The current effort focuses on the development of a three-dimensional multistage turbomachinery code, STAGE-3. STAGE-3 combines the three-dimensional algorithm used in ROTOR-4 with the database management and bookkeeping techniques developed for STAGE-2 to form a flexible and efficient code for the computation of three-dimensional flows in turbomachines with arbitrary numbers of stages. Results from the three-dimensional multi-stage turbomachinery code for a single-stage turbine configuration have been reported by Gundy-Burlet. In this paper, STAGE-3 has been used to compute the flow within a - stage turbine. Time-averaged surface pressures, surface oil-flows, and time-averaged pressure contours in the flow field of this - stage turbine are compared with experimental data where available. These results represent an initial validation of the capabilities of the STAGE-3 code to compute three-dimensional unsteady flowfields through multistage turbomachines.