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

Particle image velocimetry measurements are used to identify the unsteady f low structures and turbulence in a transparent centrifugal pump with a vane d 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 a nd in the volute. A custom-made 2 Kx2 K digital camera with a unique digita l image-shifting feature is used to record the images. For the measurements made close to design conditions, phase averaged velocity and vorticity fie lds are presented along with the corresponding turbulent stresses at differ ent impeller blade orientations (relative to diffuser vanes). The statistic ally converged results show that the entire flow field is dominated by wake s generated by impeller blades, diffuser vanes, and unsteady separation phe nomena. The boundary layer structure in the diffuser and the associated tur bulence are strongly affected by the unsteadiness generated by the impeller The impact of the impeller blade orientation includes direct effects, jett ing 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 varia tions are higher (typically twice) than the turbulent fluctuations within t he impeller and between the diffuser vanes, bur decrease below the turbulen ce level with increasing distance downstream of the trailing edge of the di ffuser vanes. [S0098-2202(00)00801-4].