B. Dewar

Research output: Contribution to conferencePaperpeer-review


This work focuses on the CAD drafting, CFD analysis in ANSYS CFX and design optimisation using Optislang of a triple exit volute for a high speed centrifugal compressor. This work came about through a research project for a small high speed air compressor to drive the pneumatic systems of an electric bus. A drafting method is detailed, the volute scroll cross section parametrised and the circumferential variation of volute cross section expressed in terms of hydraulic diameter. Different cross section variations are tested and an optimal one found with a mostly linear profile. A CFD method is presented including mesh transforms and domain interfaces, a mesh convergence study is presented as well. Due to the high speed nature of the compressor the CFD method makes use of ramped functions in CEL (CFX Expression Language) for mass flow rate, RPM and time step. Different hydraulic diameter vs circumferential position functions are tested for a vaneless diffuser of a nominal size. It was shown that a linear profile is best with a slight jump in size at the tongue. The volute profile selected was the one with the highest static pressure rise from the volute inlet to the average of the three volute outlets. The selected volute profile was then tested with vaneless diffusers of different radii. It was shown that there exists an optimal radius between static pressure diffusion and total pressure drop, the one with the highest outlet static pressure was selected as optimal, in this case 1.375 times the impeller outlet radius. A channel type diffuser vane was drafted and parametrised allowing for manipulation of its main features, such as wedge angle and vaneless space. The domain was sliced in order to allow for more efficient computation, this method was proven to reproduce acceptable results compared to a full simulation of all blade and volute passages. A design database was generated allowing for the use of Optislang optimisation software. Response surfaces and correlation coefficient were determined between the vane input variables and the objective functions of static pressure rise and thermal efficiency. A gradient based method was used to find an optimal design. The optimal vane angle was 83 degrees, wedge angle of 3.46 degrees, the vane outer radius is 124% of the impeller outlet radius and the vanless space 10% of the impeller outlet radius. The diffuser radius is re optimised with the addition of the diffuser vanes and shown that a smaller diffuser is optimal when vanes are added compared to a vaneless diffuser. Finally, the vane number is adjusted and a final optimal vaned diffuser and volute reached. In this case the optimal vane number was 29, or 1.38 times the number of total impeller blades.

Original languageEnglish
Publication statusPublished - 16 Apr 2021
Event14th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics, ETC 2021 - Gdansk, Virtual, Poland
Duration: 12 Apr 202116 Apr 2021


Conference14th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics, ETC 2021
CityGdansk, Virtual


  • Ansys CFX
  • CFD
  • Compressor
  • Diffuser Vanes
  • Optimisation
  • Volute Design

ASJC Scopus subject areas

  • Mechanical Engineering
  • Mechanics of Materials
  • Condensed Matter Physics


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