Session: 34-08 CFD and Modeling Methods

Paper Number: 152016

Application of the Pseudo-Spectral Time Marching Method to Blade Response Under Upstream Perturbations 

Turbomachinery flows are unsteady in nature. The cost of applying of conventional implicit Computational Fluid Dynamic (CFD) methods can be excessively expensive, because a significant number of time steps are required to accurately capture the unsteady phenomena. The cyclic nature of turbomachinery problems allows to capitalize on the temporal and spatial periodicity of the problem. Thus, different harmonic methods have been proposed to reduce the computational cost in time-periodic turbomachinery problems. However, a major drawback of the proposed methods to date is that they require a significant modification of the solver’s structure when departing from conventional implicit CFD solvers. This limits the widespread use of these approaches. Hence, alternative approaches that require fewer changes in the solver’s structure while maintaining the reduction in computational cost are necessary to increase the application of the harmonic methods.

In this work, a novel harmonic approach is applied to a fan stage under characteristic inlet distortion profiles for the first time. This novel approach, named as the Pseudo-Spectral Time-Marching (PSpTM) method, is based on a spectral definition of the temporal derivative through a truncated Fourier function, similar to a harmonic balance method (HB), but rearranged in a time marching fashion. This reformulation of the method, in combination with an acceleration of the dual time step convergence through a period informed approach, was designed to reduce the overall computational cost in comparison with conventional implicit approaches by reducing the number of time-steps required per period. The key advantage of this novel formulation compared with classical harmonic methods is that it requires minor modifications in the CFD solver structure.  The PSpTM method requires to define a priori the fundamental frequency of the problem, which in turbomachinery flows is conventionally related with the fan rotational speed. The PSpTM also requires defining the number of harmonics to be included in the solution which also determines the accuracy of the method.

The method was implemented into an existing unstructured edge-based, second-order, compressible RANS solver with Spalart-Allmaras used as the turbulence closure model. To benchmark the method, a well-established implicit time scheme based on a second-order backward implicit approach (BDF2) is used. Sample distortion profiles based on prescribed DC60 values are used to model the problem. The accuracy of the PSpTM method is verified by the comparison with the BDF2 baseline. The effect of the increase on the number of harmonics included in the solution is evaluated to determine the impact of this parameter in the method’s accuracy. The performance of the PSpTM method will be compared with the BDF2 approach to determine the speed-up factor.

Presenting Author: Jesus Matesanz-Garcia Universidad Politécnica de Madrid

Presenting Author Biography: Jesús Matesanz-García (Madrid, 1995) is currently based in the Universidad Politécnica de Madrid (UPM) as Post-Doctoral Researcher. He finished his Bachelor of Aerospace Engineering in the UPM in 2017, specializing in the track of propulsion. After a brief period working in the wind energy industry, Jesús moved to Cranfield University (UK) to start his PhD in Aerospace Engineering. He was based in the Centre of Thermal Power and Propulsion Engineering for 5 years, working withing the Rolls Royce UTC research centre. During his PhD studies he worked in the propulsion integration and aerodynamics for novel propulsion systems, such as boundary layer ingestion. Before finishing his studies, he started working as Fellow researcher in Cranfield, where he developed tools for aerodynamic optimization and analysis of the propulsion integration of civil aero-engines. In 2023 he moved back to Spain, where he is developing methods for unsteady aerodynamic analysis in turbomachiney, within the Gas Turbine research group of the UPM.

Authors:

Jesus Matesanz-Garcia Universidad Politécnica de Madrid
Roque Corral Universidad Politécnica de Madrid