Abstract: D turbulent flow fields in a rectangular volute of a small centrifugal compressor were measured with a hot wire probe at three across sections along its circumference at three different flow regimes.The space positions were adjusted with a three dimensional coordinate frame.Time average velocities and Reynolds stress tensors were calculated by means of a hot wire response equation with third order of precision.The measured results illustrated two recirculation regions near both side walls due to abrupt expansion at the inlet of the rectangular volute.The turbulent kinetic energy and Reynolds stresses in the recirculation regions were reduced as the flow rate increases and as the radius increases.In addition,asymmetry of the rectangular inlet induced the vortices at different cross sections of the volute,and made the trace of the flow as a curved spirochaeta.In consequence,the abrupt expansion and the asymmetry of the inlet must be avoided.