Study On Flow in Diffusers for Centrifugal Turbomachines : Report 3, Effects of Circumferential Nonuniformity of Inlet Flow

Abstract

Experiments were carried out to study diffuser performance in off-design conditions of turbomachines. Test apparatus consists of the diffuser and a set of approaching channels, which give various circumferential velocity distributions at the inlet. (1) A calculation method for boundary layer growth and diffuser performance was obtained as an extension of the calculation for logarithmic spiral diffusers. Here the main flow velocity is treated as a sum of a fundamental (log. spiral) part and an additive part. (2) In regions which are free from the direct influence of the inlet flow, forms of the secondary flow and pressure distribution are invariable regardless of variations of the inlet flow. (3) In the range of low flow-rates, the effective inlet radius becomes large and it decreases the pressure-rise. (4) It was also made clear that cases with leading edges could be treated as applications of the logarithmic spiral diffusers.