A better understanding of turbulent unsteady flows is a necessary step towards a breakthrough in the design of modern compressors. Owing to high Reynolds numbers and very complex geometry, the flow that develops in such industrial machines is extremely hard to predict. At this time, the most popular method to simulate these flows is still based on a Reynolds-averaged Navier–Stokes approach. However, there is some evidence that this formalism is not accurate for these components, especially when a description of time-dependent turbulent flows is desired. With the increase in computing power, large eddy simulation (LES) emerges as a promising technique to improve both knowledge of complex physics and reliability of flow solver predictions. The objective of the paper is thus to give an overview of the current status of LES for industrial compressor flows as well as to propose future research axes regarding the use of LES for compressor design. While the use of wall-resolved LES for industrial multistage compressors at realistic Reynolds number should not be ready before 2035, some possibilities exist to reduce the cost of LES, such as wall modelling and the adaptation of the phase-lag condition. This paper also points out the necessity to combine LES to techniques able to tackle complex geometries. Indeed LES alone, i.e. without prior knowledge of such flows for grid construction or the prohibitive yet ideal use of fully homogeneous meshes to predict compressor flows, is quite limited today.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.2013.0323

Large eddy simulation of flows in industrial compressors: a path from 2015 to 2035

Grids have been used as a means of generating nearly isotropic turbulence for about fifty years. Even so, there does not appear to be a single document which gives adequate and simple rules for the design of such devices in an airflow installation. This paper attempts to fill this gap by means of a synthesis of experimental data with simple analyses, such that useful design guidelines are derived. Pressure losses, turbulence intensities, spectra, correlation functions and length scales are all examined. The present results are found to agree well with other data published in the literature.

The generation of nearly isotropic turbulence by means of grids

The purpose is to simulate numerically the flow and noise on the Advanced Noise Control Fan (ANCF). The ANCF model was developed by the NASA Glenn Research Center to provide measurement data of a turbofan flow and its corresponding generated noise. The aim of the numerical simulations is to predict accurately the tonal noise as well as the broadband content of the ducted rotor/stator model using as a reference the provided far-field noise measurements.

Noise Predictions of the Advanced Noise Control Fan Using a Lattice Boltzmann Method and Ffowcs Williams–Hawkings Analogy

This work was supported by the EPSRC through an iCASE award sponsored by Rolls-Royce plc. Rolls-Royce plc are gratefully acknowledged for allowing the use and modification of their CFD solver HYDRA. The work used the ARCHER UK National Supercomputing Service (http://www.archer.ac.uk) under EPSRC grant EP/L000261/1, and thanks go to both for their support.

Towards predictive eddy resolving simulations for gas turbine compressors

Effects of rotor height on the performance and flow features of mixed-flow type compressors

Axial compresso rs are often subject to poor inflow conditions which range from steady state , but spatially asymmetric velocity profiles due to imperfect intake geometry to time varying ingested vortices, turbulence or secondary inflow distortion s. The resulting periodic and/or random forces acting on the blades cause tonal and/or broadband interaction noise which sometimes dominates the noise radiation of the compressor . In th e present study, we appl y the large eddy simulation (LES) method to pre dict the unsteady forces on the blades of a single stage low pressure axial flow compressor without guide vanes. T urbulence is generated by a turbulence grid installed upstream of the impeller’s leading edge plane. The LES shows that the complex wake/vorte x flow downstream of the turbulence grid produces both , “random” (i.e. broadband) and periodic velocity fluctuations. The predicted blade response to the inflow turbulence (in terms of surface pressure fluctuations in the blade leading edge region) is in g ood agreement with our own surface pressure measurements. Assuming the impeller to be placed in an infinitely long duct a simple algebraic acoustic model proposed by Morfey is employed to predict the duct sound spectrum . By way of contrast, assuming a very short duct type inlet , the Ffowcs Williams and Hawkings analogy is employed to predict the spectral free field suction side sound pressure. Employing the LES data the acoustic calculation s yield a good first estimate of the absolute levels of the radiated sound. Also, the characteristic differences between clean inflow (i.e. without turbulence grid) and highly turbulent inflow are reasonably well predicted as compared to experiments. Discrepancies are attributed to insufficient boundary layer reso lution , t he omission of the tip clearance , and the limitations of the acoustical model s.

H. Reese

Papers

Large Eddy Simulation of Gust Noise Sources in a Low Pressure Axial Compressor