A Multi Blade-Row Linearised Analysis Method for Flutter and Forced Response Predictions in Turbomachinery

Abstract

A three-dimensional time-linearised unsteady Navier-Stokes solver is presented for the computation of multistage unsteady flow in turbomachinery. The objective is to address multistage aeroelastic effects for both flutter and forced response. Since the method is currently being developed, only forced response applications are studied in this paper. With this approach, travelling waves, known as spinning modes, are propagated across the multistage domain in order to take into account the interaction between the blade-rows. The method is first validated over two simple test cases for which analytical solutions were available. It is then tested on a turbine stage test case and multistage effects are evaluated from the contribution of one spinning mode included in the model. The results are compared with both time-linearised single-row and nonlinear multirow methods. Multi-row effects are shown not to be important in this case. However, the test case serves as a validation for the implementation of the methodology and further work will focus on the implementation of several spinning modes and the computations of forced response and flutter cases with several blade-rows.

Acoustic scattering by cascades with complex boundary conditions: compliance, porosity and impedance

“…Aspirations for lighter and more efficient engines have driven the design of thinner and lighter blades in turbomachinery (Saiz 2008). As a result, aeroelastic effects such as flutter and resonance must be considered in modern turbomachinery design and testing (Hall, Kielb & Thomas 2006).…”

Computational aeroelastic modelling of airframes and turbomachinery: progress and challenges

“…Notable methods based on this feature are those by Cizmas & Hall (1995), Holmes et al (1997), Ning (1998) and Sbardella & Imregun (2000) for turbomachinery applications. A method which takes into account multistage effects in turbomachinery was developed for inviscid flows by Silkowski & Hall (1998) and Hall & Kivanc (2005) and later extended along this vein to viscous flows for rotor stator interaction by He et al (2002) and to multiple blade row viscous flows by Saiz et al (2006).…”

Flutter analysis of a one-and-a-half-stage fan at low speed using nonlinear harmonic method

“…Their results show that the aero-damping can be significantly influenced by the gap size. Ekici et al, 8 Saiz et al, 9 and Sotillo and Gallardo 10 developed their own time linearized Navier-Stokes solvers to analyze the multirow effects, especially the acoustic reflection. Rahmati and He 11 developed a nonlinear time-domain solver as well as a frequency-domain solver and validated the code with two test cases.…”

“…This method was first proposed by He and Ning. 13 Similar to the 3D time linearized solver in Ekici et al, 8 Saiz et al, 9 and Sotillo and Gallardo, 10 the idea of the NLH method is that flow variables are decomposed into time-mean value and a sum of periodic perturbations, which are then Fourier decomposed in time into several harmonics. Then, the unsteady Reynolds-averaged Navier-Stokes (RANS) equation is casted into the frequency domain.…”