Efficient Time Resolved Multistage CFD Analysis Applied to Axial Compressors

Abstract

Unsteady computations are necessary if blade row interactions effects are relevant, for example for detailed optimization of a compressor at off-design conditions towards the aerodynamic stability limit, or for structural mechanical tuning of the blades. Modeling time accurate transient multistage flow is expensive both in terms of computer time and memory. Recently the implicit time-resolved Time Transformation method (based on Giles’ time inclining) has been shown to be computationally efficient and a good alternative for modeling transient flow in a single stage (one pitch ratio) turbomachinery configuration. A further advantage of this time resolved method is its ability to capture not only blade passing frequencies but also self-excited frequencies such as in wakes and tip vortex shedding. In this work, an extension of the Time Transformation method (TT) to multistage modeling has been employed to assess the method’s ability in predicting modern multistage compressor performance speedline curve, as well as its ability in capturing dominant machine frequencies. The multistage TT method is verified on a two and a half stage modified Hannover compressor, followed by an industrial validation on a Siemens Energy half scale six stage axial compressor based on the last stages of the Siemens Platform Compressor (PCO). Reference transient solutions on reduced portions of the compressor and/or modified blade count solutions are obtained and compared directly to single passage multistage Time Transformation predictions for the Hannover compressor. The method is then applied directly to the full six stage Siemens compressor employing the true blade counts for all six stages. The first goal of this work is to investigate the ability and accuracy of the multistage TT method to capture all relevant blades passing frequencies, including the impact of different degrees of pitch change between components. The second goal of this work is to explore how best to apply the method for the prediction of a compressor map, up to the surge line. Solutions are compared to experimental test rig data. Physical explanations of the key flow features observed in the experiment, as well as of the differences between the predictions and experimental data, are given.

Application of the Time-Transformation Method for a Detailed Analysis of Multistage Blade Row Interactions in a Shrouded Turbine

“…These results are not included in this work but looked promising compared to a reference calculation. For additional disturbances we saw erroneous frequencies coming up, like Cornelius et al (2013Cornelius et al ( , 2014 observed as well.…”

“…In the literature the TT method has shown very promising results in terms of predicting turbo machinery performance data as Biesinger et al (2010) demonstrated by the example of a one stage case (inlet guide vane (IGV) and rotor) of the 1.5 stage transonic Purdue compressor and later on the full 1.5-stage case (Biesinger et al (2012)). Cornelius et al (2013Cornelius et al ( , 2014 investigated the multistage extension of the TT method on a modified 2.5-stage version of the 4-stage axial Hannover Compressor and a Siemens 6-stage axial compressor rig ("PCO Rig"). The performance data revealed very good correlation with the experimental data and numerical reference calculations.…”

An Efficient Approach for Predicting Resonant Response with the Utilization of the Time Transformation Method and the Harmonic Forced Response Method

“…The amplitude and phase angle of the loads are determined by fast Fourier transform (FFT) analysis. The out-of-phase loads are specified in real and imaginary components, as shown in Equation (19). Then, the Equation ( 17) can be rewritten in Equation (21), which calculates only the steady-state vibration response of the structure.…”

“…The TT method was validated on several test cases [12,[18][19][20]. However, the discussion of this method in the open literature was more concerned about the total performance parameters (mass flow, efficiency, and total pressure ratio) and time-averaged variables.…”

Assessment of curvature correction and reattachment modification into the shear stress transport model within the subsonic axial compressor simulations

“…11 Hence, in recent years, the SST-RM model has been frequently used to investigate various issues in different geometries. [12][13][14] However, up to now, most of the assessment of the SST-CC and SST-RM models were conducted in simple cases, such as wing tip vortex flow, 5 rotating channel flow, 5,15,16 and diffuser flow. 11 In turbomachines, the flows are usually more complicated and affected by multiple factors, such as strong adverse pressure gradient effect, high curvature effect, intense rotating effect, and also complicated 3D separations, hence, the assessments of SST-CC and SST-RM models in such cases are extremely challenging and should be conducted with caution.…”