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The initial conceptual design of centrifugal fan and compressor volutes is considered and extended to accommodate overhung volute designs often used in process and turbocharger compressors. The initial passage design is then developed through the application of a commercial computational fluid dynamics (CFD) code. Based on the experimental data of a turbocharger compressor volute, three-dimensional, compressible, steady flow computations were carried out for alternative volute designs. Detailed internal flow data in both a conventional and a modified volute design, at both design and off-design flow conditions, are presented. The design investigation showed that enlarging the flow passage area near the tongue region, but without changing the exit-inlet area ratio of the volute, led to an improvement in the internal flow distribution at off-design flow conditions. NOTATION 1 INTRODUCTIONA spiral-shaped volute which collects the flow from the B width of vaneless diffuser (m) diffuser and passes it to a single discharge pipe is a basic C absolute velocity (m/s) component of centrifugal compressors and fans. C r radial velocity component (m/s) Assessment of the design and performance of the col-C h tangential velocity component (m/s) lecting volute has received only limited investigation. The P static pressure (Pa) volute is usually designed through the application of a oneq v flowrate (m3/s) dimensional analysis assuming a free vortex flow from the Q m mass flowrate (kg/s) volute inlet to the centre of the volute passage [1]. The r radius of volute passage sectional circle (m) design objective is to achieve a uniform flow at volute inlet. R radius from impeller axis to any arbitrary This is usually attained at the design flowrate only; at offposition in the volute passage (m) design conditions the volute is either too small or too large R c radius from impeller axis to centroid of volute and a pressure distortion develops circumferentially passage (m) around the volute passage. At low flowrates the pressure a angle from the radial direction (deg) increases with azimuth angle while at high flowrates the h volute azimuth angle (deg) pressure decreases. These circumferential pressure distortions are transmitted back to the impeller discharge and have been observed at impeller inlet. The pressure distorSubscripts tions reduce the stage performance and have a direct impact on diffuser and impeller flow stability. Yao et al. d volute discharge [2] and Qi et al. [3] described a volute design technique 3 vaneless diffuser inlet/impeller discharge that allowed a controlled distribution of the volute inlet 4 volute inlet/vaneless diffuser discharge flow angle, leading to the development of an 'optimum' volute design and improved fan performance. In recent years three-dimensional viscous compuThe MS was received on 8 September 1997 and was accepted after tational fluid dynamics (CFD) codes have been used revision for publication on 2 June 1998. to study the internal flows of volutes [4-6 ]. The com-* Corresponding author: Depa...

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