A study of the unsteady flow in an axial flow turbine stage with a second stator blade row is presented. The low aspect ratio blades give way to a highly three-dimensional flow which is dominated by secondary flow structures. Detailed steady and unsteady measurements throughout the machine and unsteady flow simulations which include all blade rows have been carried out. The presented results focus on the second stator flow. Secondary flow structures and their origins are identified and tracked on their way through the passage. The results of the time-dependent secondary velocity vectors as well as flow angles and Mach number distributions as perturbation from the time-mean flow field are shown in cross-flow sections and azimuthal cuts throughout the domain of the second stator. At each location the experimental and numerical results are compared and discussed. A good overall agreement in the time-dependent flow behaviour as well as in the secondary flow structures is stated. ' fluctuation

This paper presents a computational method for the calculation of unsteady three-dimensional viscous flow in turbo-machinery stages. The method is based on a Finite-Volume Navier-Stokes solver for structured grids in a multiblock topology. The meshes at the stator/rotor interface are overlapped by two grid cells. An implicit residual smoothing method applicable to global time-stepping is used to accelerate the solution process. The problem of periodic boundary treatment for unequal pitches is handled using a method of time-inclined computational domains for three dimensions. The method applies a time transformation to the stator domain and to the rotor domain and uses different time-steps in the two domains. The results of a numerical simulation of the flow in a transonic turbine stage with a pitch ratio of 1.364 are presented. The time-averaged solution is compared to experimental data and satisfactory agreement is stated. Complex 3D-unsteady flow phenomena (shock motion, vortex shedding) are observed. Unsteady blade pressure fluctuations at various positions in spanwise direction are shown and the fluctuations are found to vary considerably along span. Instantaneous distributions of static pressure, Mach number, and entropy are presented.

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A numerical method to solve the three-dimensional Navier-Stokes equations for the flow in transonic turbine stages with tip gap leakage is presented. Viscous flow in a transonic turbine stage has been simulated. The high pressure difference at the rotor blade tip results in a supersonic jet. The relative motion of the casing wall is oriented against the tip leakage flow and tends to reduce it. Very large velocity gradients in the tip region pose a challenge for the numerical simulation. Computational results are compared with experimental data obtained in operation. Measurements include data for the tip leakage jet. The numerical method is based on a conservative finite volume cell–vertex scheme in cylindrical coordinates with central difference approximation and Runge–Kutta time stepping. Convergence is accelerated by use of a multigrid method and implicit residual smoothing with variable coefficients. The Baldwin–Lomax turbulence model is used for closure. The boundary condition treatment at inlet and outlet as well as the coupling of stator and rotor flow is achieved by use of non–reflective boundary conditions. The tip region is discretized by an additional grid within a multi-block approach.

To investigate the three-dimensional unsteady flow and the turbulence intensities behind rotating blade rows of turbomachines, a procedure using a fast-response pressure probe has been developed. The integration of the cylindrical miniature pressure transducers into the probe head minimizes the risk of mechanical damage. The dynamic behaviour of the probe was analyzed. The application of the probe to the rotor exit flow of an axial compressor is described and results are presented.