This paper presents the implementation of a non-reflecting boundary condition for steady and unsteady turbomachinery flow computations. Here, the truncation of the computational domain can lead to spurious numerical reflections due to artificial open boundary surfaces. To face this issue, Giles introduces a popular set of non-reflecting boundary conditions for turbomachinery applications. Whereas the steady formulation is exact within the linearisation approach, Giles suggests an approximate boundary condition for unsteady simulations. Resulting from this approximation, the unsteady boundary conditions are not perfectly nonreflecting. Thus, steady and time averaged unsteady flow solutions do not necessarily coincide, even if the flow field contains no unsteadiness.We suggest a single boundary condition formulation suitable for steady and unsteady simulations. This approach applies a modal decomposition and, thus, undesired incoming modes can easily be ruled out. Steady modes can be handled as in the steady case. Apart from the assumptions made by starting from the linearised, two-dimensional Euler equations, this approach does not require any further approximation, and, therefore, the time-averaged unsteady and the steady solutions coincide in the limit of steady flows.We apply and assess the presented boundary condition in steady and unsteady computations of two turbomachinery test cases.
The aim of this study was to assess the capabilities of different simulation approaches to predict the flutter stability of a steam turbine rotor. The focus here was on linear and nonlinear frequency domain solvers in combination with the energy method, which is widely used for the prediction of flutter onset. Whereas a GMRES solver was used for the linear problem, the nonlinear methods employed a time-marching procedure. The solvers were applied to the flutter analysis of the first rotor bending mode of the open Durham Steam Turbine test case. This test case is representative of the last stage of modern industrial steam turbines. We compared our results to those published by other researchers in terms of aerodynamic damping and local work per cycle coefficients. Time-domain, harmonic balance, and time-linearised methods were compared to each other in terms of CPU efficiency and accuracy.
The aim of the present work is to facilitate insight into the modeling errors in the context of blade row coupling approaches which capture unsteady flow phenomena at different levels of detail. The focus is on RANS-based steady mixing plane computations as well as time domain and frequency domain unsteady computations. The concept of mixing loss is revisited to quantify the amount of unsteadiness in a flow field. Following an idea by Fritsch and Giles, we compute a second order approximation of the mixing losses which are generated at blade row interfaces. The resulting formula decomposes the entropy jump into contributions of circumferential and temporal fluctuations. The mathematical derivation, however, is based upon simpler arguments. It is shown that Fritsch and Giles’ main result can be extended to non-ideal gases. Moreover, the second order mixing loss formula is applied to time and frequency domain unsteady simulations. It is shown that an additional term has to be computed which accounts for the interaction of evanescent acoustic modes if the method is applied to unsteady flows. The methodology decomposes the overall mixing entropy into contributions of single perturbation types and harmonics. This may be used to assess whether unsteady flow phenomena of interest are adequately resolved and, in particular, to quantify the unsteadiness contained in the unresolved harmonics. A detailed investigation of the transonic IGV-rotor configuration of DLR’s Rig 250 compressor demonstrates the approach.
The flow field of a Ranque-Hilsch vortex tube is characterized experimentally. Firstly conventional probe based technology is used in order to measure inlet and outlet temperatures as well as to acquire temporally resolved wall pressure data over a wide range of operating conditions. Secondly the filtered Rayleigh scattering technique is employed in order to gather detailed temporally averaged planar information on the vortex tube's flow topology. These measurements form the basis of a detailed numerical study in part II of this contribution.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.