Application of flow control on a radial compressor for operating range extension

The application of flow control (strategic injection and/or extraction of small amounts of fluid relative to the main flow) on compressors has mainly been evaluated for axial compressors to the present date. By injecting or recirculating a fraction of the main flow a benefit in terms of a significant increase in the stable operating range has been demonstrated. This paper presents an experimental study of the application of flow control on a radial compressor. High momentum flow is injected continuously through a discrete number of holes upstream of the leading edge of an unshrouded impeller with the aim to delay the inception of stall and surge. Overall three flow control modes were tested: Controlled injection, controlled extraction and a combination of controlled injection and extraction. After modifying the compressor stage the onset of two distinct rotating stall patterns could be suppressed by flow control and stall and surge margins were increased, though by a lesser amount than for axial compressors.