Testing and adaptation of new approaches to unsteady flow simulation for aerodynamic problems
Aerospace propulsion engineering
Аuthors*, **, ***
United Engine Corporation “Saturn”, 163, Lenin av., Rybinsk, Yaroslavl region, 152903, Russia
Results of unsteady flow simulation for 1½ model turbine stage are considered. For cases with unequal numbers of blades/vanes in adjacent rows (“unequal pitch”) a computation over multiple passages is required to ensure that simple periodic boundary conditions can be applied. For typical geometries, a time accurate solution requires computation over a significant portion of the wheel or full wheel. It require prohibitive computing resources and becomes problematical especially for aviation industry with hard regulated times of developing. In this case it is necessary to use some simplifications (change number of blades, geometric and gas-dynamic scaling, transformation of problem to 2D simulation), which may result in inaccuracy in developing, because this technique is not allow to correctly simulate interaction of blade rows with unequal blade pitch. A number of methods are now available that address the issue of unequal pitch while significantly reducing the required computation time. Considered here are a family of related methods (“Transformation Methods”) which transform the equations, the solution or the boundary conditions in a manner that appropriately recognizes the periodicity of the flow, yet do not require solution of all or a large number of the blades in a given row. This paper will concentrate on comparing and contrasting these numerical treatments. The first method, known as “Profile Transformation”, overcomes the unequal pitch problem by simply scaling the flow profile that is communicated between neighboring blade rows, yet maintains the correct blade geometry and pitch ratio. The next method, known as the “Fourier Transformation” method applies phase shifted boundary conditions. To avoid storing the time history on the periodic boundary, a Fourier series method is used to store information at the blade passing frequency and its harmonics. In the final method, a pitch-wise time transformation is performed that ensures that the boundary is truly periodic in the transformed space. This method is referred to as “Time Transformation”. The three methods are realized in ANSYS CFX v.14 solver. Verification of used technique and comparison of simulation results with results of full mesh simulation is also presented in this paper.
Keywords:unsteady flow, turbomachine, blade row, rotor-stator interaction, profile transformation, time transformation, Fourier transformation, 3D simulation
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