A Numerical Method for Turbulent Flows in Highly Staggered and Low Solidity Supersonic Turbine Cascades

Abstract

Two main problems are associated with conventional numerical methods for simulating turbulent flows in high-reaction-type supersonic turbine cascades near the tip of the last stage blade in a steam turbine: the large skewness of computational grids and treatments of boundary conditions when the shock waves hit boundaries. This paper presents a numerical method to deal with these issues. A grid generation technique which uses five-block structured grids has been developed. The orthogonality of the grid is good even for highly staggered and low solidity cascades. In addition, the grids are completely continuous at the boundary between the blocks and at the periodic boundaries. Both the gradient of the grid lines and the change rate of the grid widths connected smoothly. As a result, shock waves can be captured accurately and stably. The inflow and outflow boundary conditions based on the two-dimensional characteristic theory have been applied and diminished the spurious reflections and fluctuations of shock waves at both the inlet and outlet boundaries. Therefore the non-physical reflection does not affect the flow in the cascades. A low Reynolds number k-ε turbulent model has been proposed. Distance from a wall is not used as the characteristic length of turbulent flows so that the turbulent model can be applied to a wake and a separation flow. The validity of the numerical method was verified by comparisons of the pressure distributions on the blade, the loss coefficients, and flow angles with linear cascade experiments of transonic compressor cascades.

Advances in axial turbine blade profile aerodynamics

“…It offers advantages, for example, better understanding of flow features related to turbine profiles, and quick and less expensive process. Recently, a number of numerical investigations deal with turbine blade boundary layer flow characteristics, wake passing effects, blade profile loss prediction, flow control on turbine blade profiles, design optimization methods for blade profiles, and so on, using RANS 91,92 (Figures 16 and 17), LES, 30 or even DNS 93 (Figure 18).…”

“…Therefore, although the RANS results are quite promising, there is still space for performance improvement in the transition and turbulence models, especially in low Reynolds number applications. 91,92 As the computational power increases, the application of LES becomes more popular for understanding the complex flow physics of turbine blade profiles, and to overcome the deficiencies of RANS simulations. Since the LES method is inherently an unsteady analysis and capable of time-dependent capturing of highly resolved motions associated with blade separated flows, it does not contain any transition modeling, regardless of separation-induced or disturbance-induced ones.…”

Development of Titanium 3600rpm-50inch and 3000rpm-60inch Last Stage Blades for Steam Turbines

“…Features of three types of aerofoils are described as follows. Mach number contours for subsonic aerofoils near the hub are calculated by a two-dimensional (2D) turbulent flow analysis code, which is the internally developed CFD software named TURBO2D (Senoo and White, 2006;Senoo et al, 2011), and shown in Fig. 11.…”