J0501-1-5 Numerical Study of Performance Improvement of Partial Admission Stage based on the Unsteady Flow Simulation
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This paper presents a numerical study for unsteady flows in a high-pressure steam turbine with a partial admission stage. Compressible Navier-Stokes equations are solved by the high-order high-resolution finite-difference method based on the fourth-order compact MUSCL TVD scheme, Roe's approximate Riemann solver, and the LU-SGS scheme. The SST-model is used for evaluating the eddy-viscosity. As numerical examples, unsteady two-dimensional flows in a partial admission stage of steam turbine are calculated. The effect of the nozzle box flange to the lift of rotors is numerically investigated. The performance of several types of partial admission stage is parametrically predicted. The efficiency was improved by the sloping flange.Keywords:
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Compressible flow
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Abstract A five‐equation model for compressible two‐fluid flow is proposed, that is based on physical flow equations only. The model is conservative and pressure‐oscillation free. Equations for continuous flow and jump conditions for discontinuities are given, as well as a discretization of the equations and an adaptation of the HLL Riemann solver to two‐fluid flow. Numerical tests in 1D and 2D show the accuracy of the method. Copyright © 2005 John Wiley & Sons, Ltd.
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Abstract An approximate Riemann solver is presented for the compressible flow equations with a general (convex) equation of state in a duct of variable cross‐section and within a Lagrangian frame of reference. The scheme is applied to a well‐known shock tube problem.
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In this article we introduce a new Riemann solver for traffic flow on networks.The Priority Riemann solver (PRS) provides a solution at junctions by taking into consideration priorities for the incoming roads and maximization of through flux.We prove existence of solutions for the solver for junctions with up to two incoming and two outgoing roads and show numerically the comparison with previous Riemann solvers.Additionally, we introduce a second version of the solver that considers the priorities as softer constraints and illustrate numerically the differences between the two solvers.
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A novel five-equation model for inviscid, non-heat-conducting, compressible two-fluid flow is derived, together with an appropriate numerical method. The model uses flow equations based on conservation laws and exchange laws only. The two fluids exchange momentum and energy, for which source terms are derived from fundamental physical laws. The Riemann invariants of the governing equations are derived, and used in the construction of an Osher-type approximate Riemann solver. A consistent finite-volume discretization of the source terms is proposed. The source terms have distinct contributions in the cell domain and at the cell faces. For the source-term evaluation at the cell faces, the Riemann solver is elegantly exploited. Numerical results are presented for shock-tube and shock-bubble-interaction problems. The resemblance with experimental results is very good. Free-surface pressure oscillations do not occur, without any precaution. The paper contributes to state of the art in computing two-fluid flows.
Inviscid flow
Compressible flow
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Roe solver
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Octree
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A cell-centered spatiotemporal coupled method is developed to solve the compressible Euler equations. The spatial discretization is performed using an improved weighted essentially non-oscillation scheme, where the Harten–Lax–van Leer–contact approximate Riemann solver is used for computing the numerical fluxes. A two-stage fourth-order scheme is adopted to carry out time advancement for unsteady problems. The proposed method is featured by spatiotemporal coupling time-stepping that can be generalized without using the case-dependent generalized Riemann problem solver. A number of one- and two-dimensional test cases are presented to demonstrate the performance of the proposed method for solving the compressible Euler equations on structured grids. The numerical results indicate that the novel method can achieve relatively large Courant–Friedrichs–Lewy (CFL) number compared to other studies that implement the two-stage fourth-order scheme, and that it is more capable of capturing small-scale flow structures than the Runge–Kutta (RK) method.
Compressible flow
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Oscillation (cell signaling)
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