Quantitative visualization of the flow in a centrifugal pump with diffuser vanes - I: On flow structures and turbulence

Particle image velocimetry measurements are used to identify the unsteady flow structures and turbulence in a transparent centrifugal pump with a vaned diffuser. The experiments are being performed in a special facility that enables simultaneous measurements of the flow between the impeller blades, the gap between the impeller and the diffuser, between the diffuser vanes and in the volute. A custom-made 2 Kx2 K digital camera with a unique digital image-shifting feature is used to record the images. For the measurements made close to design conditions, phase averaged velocity and vorticity fields are presented along with the corresponding turbulent stresses at different impeller blade orientations (relative to diffuser vanes). The statistically converged results show that the entire flow field is dominated by wakes generated by impeller blades, diffuser vanes, and unsteady separation phenomena. The boundary layer structure in the diffuser and the associated turbulence are strongly affected by the unsteadiness generated by the impeller The impact of the impeller blade orientation includes direct effects, jetting ahead and a trailing wake behind the blade, as well as indirect effects, such as two types of flow separation within the diffuser The cyclic variations are higher (typically twice) than the turbulent fluctuations within the impeller and between the diffuser vanes, bur decrease below the turbulence level with increasing distance downstream of the trailing edge of the diffuser vanes. [S0098-2202(00)00801-4].