Multi-Disciplinary Optimization of a Mixed-Flow Compressor Impeller

Abstract

In this paper the procedure and results of the aeromechanical optimization of a mixed-flow compressor impeller to be used in a 600 N micro gas turbine (MGT) are presented. Today’s unmanned aerial vehicles (UAVs) demand high thrust-to-weight ratios and low engine frontal area. This may be achieved using mixed-flow compressors. The initial impeller design was obtained using a 1-D turbomachinery layout tool. A multi-point optimization of the impeller aerodynamic performance was completed, followed by a mechanical optimization to reduce mechanical stresses in the impeller. A coupled aero-mechanical optimization was concluded with the purpose of increasing the choke limit and reducing stresses while conserving aero-performance. Subsequently, a modal analysis of the rotor was conducted to determine its vibrational characteristics. The optimization process was set up and controlled in an integrated environment that includes a 3-D Navier-Stokes flow solver and a 3-D finite element (FE) structural solver. The optimization process is based on the use of a database, an artificial neural network (ANN), a user-defined objective function and a genetic algorithm (GA). The overall optimization process achieved an increase in pressure ratio (total-to-total) of 30.6% compared to the initial design while the efficiency (isentropic total-to-total) was increased by 5% at design conditions. A decrease in the surge margin was experienced, but the final surge margin was still acceptable (12%). The choke limit was increased meaningfully. This was achieved while also decreasing the peak von Mises stress from far above the material yield strength to 30% below the yield limit.

A Large Design Space Multidisciplinary Optimization of a Mixed Flow Micro Gas Turbine Compressor Stage

“…This negated the need for a separate 90 • bend and axial de-swirlers as required in purely radial diffusers. Diener et al (2016) initiated research at Stellenbosch University focused on mixed flow MGT compressors. Diener performed a CFD optimization of a mixed flow impeller for an increased thrust output requirement of 600 N. Kock (2017) further modified the MLC for the design of a mixed flow crossover diffuser suited to the impeller developed by Diener et al (2016).…”

“…Diener et al (2016) initiated research at Stellenbosch University focused on mixed flow MGT compressors. Diener performed a CFD optimization of a mixed flow impeller for an increased thrust output requirement of 600 N. Kock (2017) further modified the MLC for the design of a mixed flow crossover diffuser suited to the impeller developed by Diener et al (2016). Kock determined that the crossover diffuser outperforms a vaneless diffuser fitted with de-swirling vanes.…”

“…Bindeman (2019) adapted the MLC for use with mixed flow impellers. This was done by implementing a new slip model and a new method of calculating the impeller throat area to better match with CFD results of the impeller designed by Diener et al (2016). Swanepoel (2018) experimentally tested the crossover compressor developed by Kock (2017) at a reduced speed of 50 000 RPM (design speed of 95 000 RPM) due to testing facility limitations.…”

A Large Design Space Multidisciplinary Optimization of a Mixed Flow Micro Gas Turbine Compressor Stage

“…Bindeman 2019adapted the MLC for use with mixed flow impellers. This was done by implementing a new slip model and a new method of calculating the impeller throat area to better match with CFD results of the impeller designed by Diener et al (2016).…”

Development of Efficient Compressors for Turbochargers

“…The time taken for this exercise was a cumulative CPU time of 28 days with 4 CFD solvers running on 64 cores. Multi-disciplinary optimization of compressors has been presented recently by Perrone et al [12] for a centrifugal compressor and by Diener et al [13] for a mixed flow compressor. These studies involved a large number of calculations.…”