Jianjun Feng

Unsteady Flow Visualization at Part-Load Conditions of a Radial Diffuser Pump: by PIV and CFD

The present study provides flow visualization on complex internal flows in a radial diffuser pump under part-load conditions by using the three-dimensional Navier-Stokes code CFX-10 with Detached Eddy Simulation (DES) turbulence model. Particle Image Velocimetry (PIV) measurements have been conducted to validate numerical results. The CFD results show good agreements with experimental ones on both the phase-averaged velocity fields and turbulence field. The detailed flow analysis shows that no separation occurs at 0.75Qdes although a low-velocity zone develops on the rear impeller suction side. Steady flow separations are observed on the impeller suction sides at 0.5Qdes but with different onsets and amounts. When reducing the flow rate to 0.25Qdes, CFD predicts different types of back flows in the impeller region, including steady leading edge separations, rotating vortex in the impeller wake region, and back flow on the impeller pressure side.

Numerical Investigation on Pressure Fluctuations for Different Configurations of Vaned Diffuser Pumps

Numerical simulations on impeller-diffuser interactions in radial diffuser pumps are conducted to investigate the unsteady flow, and more attention is paid to pressure fluctuations on the blade and vane surfaces. Calculations are performed at different operating points, different blade number configurations, and different radial gaps between the impeller and diffuser to examine their effects on the unsteady flow. Computational results show that a jet-wake flow structure is observed at the impeller outlet. The biggest pressure fluctuation on the blade is found to occur at the impeller trailing edge, on the pressure side near the impeller trailing edge, and at the diffuser vane leading edge, independent of the flow rate, radial gap, and blade number configuration. All of the flow rate, blade number configuration, and radial gap influence significantly the pressure fluctuation and associated unsteady effects in the diffuser pumps.

Investigation of Periodically Unsteady Flow in a Radial Pump by CFD Simulations and LDV Measurements

The periodically unsteady flow fields in a low specific speed radial diffuser pump have been investigated both numerically and experimentally for the design condition (Q des ) and also one part-load condition (0.5Q des ). Three-dimensional, unsteady Reynolds-averaged Navier―Stokes equations are solved on high-quality structured grids with the shear stress transport turbulence model by using the CFD (computational fluid dynamics) code CFX-10. Furthermore, two-dimensional laser Doppler velocimetry (LDV) measurements are successfully conducted in the interaction region between the impeller and the vaned diffuser, in order to capture the complex flow with abundant measurement data and to validate the CFD results. The analysis of the obtained results has been focused on the behavior of the periodic velocity field and the turbulence field, as well as the associated unsteady phenomena due to the unsteady interaction. In addition, the comparison between CFD and LDV results has also been addressed. The blade orientation effects caused by the impeller rotation are quantitatively examined and detailedly compared with the turbulence effect. This work offers a good data set to develop the comprehension of the impeller-diffuser interaction and how the flow varies with relative impeller position to the diffuser in radial diffuser pumps.

Comparison of Periodic Flow Fields in a Radial Pump among CFD, PIV, and LDV Results

The interaction between the impeller and the diffuser is considered to have a strong influence on the unsteady flow in radial pumps. In this paper, the unsteady flow in a low specific speed radial diffuser pump has been simulated by the CFD code CFX-10. Both Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) measurements have been conducted to validate the CFD results. Both the phase-averaged velocity fields and the turbulence fields obtained from different methods are presented and compared, in order to enhance the understanding of the unsteady flow caused by the relative motion between the rotating impeller and the stationary diffuser. The comparison of the results shows that PIV and LDV give nearly the same phase-averaged velocity fields, but LDV predicts the turbulence much clearer and better than PIV. CFD underestimates the turbulence level in the whole region compared with PIV and LDV but gives the same trend.

Qualitative Comparison between Numerical and Experimental Results of Unsteady Flow in a Radial Diffuser Pump

Comparison between numerical simulation and experimental results for unsteady flow field in a radial diffuser pump is presented for the design operating point. The numerical result is obtained by solving three-dimensional, unsteady Reynolds-averaged Navier-Stokes equations by the commercial CFD code CFX-10 withk-ω based shear stress transport turbulence model. Two-dimensional PIV measurements are conducted to acquire the experiment result. The phase-averaged velocity and turbulent kinetic energy fields are compared in detail between the results by the two methods in the impeller, diffuser and return channel regions. The qualitative comparison between CFD and PIV results is quite good in the phase-averaged velocity field. Although the turbulence level by PIV is higher than that by CFD generally, the main turbulence features are nearly the same. Furthermore, the blade orientation effect and other associated unsteady phenomena are also examined, in order to enhance the understanding on impeller-diffuser interaction in a radial diffuser pump.

Investigation of turbulence and blade orientation effects in a radial diffuser pump by laser Doppler velocimetry

Abstract In this article, the unsteady flow field in a radial diffuser pump has been investigated by laser Doppler velocimetry measurements at the design condition Qdes and also at three off-design conditions 0.5Qdes, 0.75Qdes, and 1.15Qdes. Both the upstream effect and the downstream effect originating from the unsteady interactions are quantitatively examined, and these effects are also compared with the turbulence effect. The analysis of the experimental results shows that the upstream effect is only limited to the impeller rear part for all examined flowrates. The downstream effect is comparable to the turbulence effect before the diffuser inlet throat at Qdes and 1.15Qdes. However, the turbulence effect dominates totally over the downstream effect at part-flow conditions 0.5Qdes and 0.75Qdes.

Time-Resolved Particle Image Velocimetry (PIV) Measurements in a Radial Diffuser Pump

The truly time-variant unsteady flow in a low specific speed radial diffuser pump stage has been investigated by time-resolved Particle Image Velocimetry (PIV) measurements. The measurements are conducted at the midspan of the blades for the design condition and also for some severe part-load conditions. The instantaneous flow fields among different impeller channels are analyzed and compared in detail, and more attention has been paid to flow separations at part-load conditions. The analysis of the measured results shows that the flow separations at two adjacent impeller channels are quite different at some part-load conditions. The separations generally exhibit a two-channel characteristic.Copyright

Experimental investigation of velocity fluctuations in a radial diffuser pump

The strong interaction in a radial pump due to the relative movement between the impeller and the diffuser may excite not only strong pressure fluctuations but also velocity fluctuations. In this paper, the laser Doppler velocimetry (LDV) technique is successfully applied to measure the periodic flow field in a radial diffuser pump with low-specific speed, in order to investigate the velocity fluctuations caused by the impeller-diffuser interactions both in the impeller and diffuser regions. The velocity fluctuations in the impeller region are quantitatively examined at different radial positions, and the flow structure at the radial gap between two flow components is analyzed at different relative positions. In addition, the downstream effect on the diffuser flow is quantitatively and qualitatively assessed and compared with the turbulence effect.

Experimental Investigation on Turbulence Fields in a Radial Diffuser Pump Using PIV Technique

Particle image velocimetry (PIV) technique has been successfully employed to measure the unsteady periodic flow in a lowspecific speed radial diffuser pump, in order to obtain turbulence intensity fields caused by rotor-stator interaction at different operation conditions. The PIVmeasuring region covers a complete impeller channel and a complete diffuser channel, enabling the investigation of turbulence behavior in both the impeller and diffuser region simultaneously, and the turbulence transportation from the upstream impeller wake to the diffuser region. In addition, the flow rate effect on the turbulence field has also been investigated by comparing measured turbulence fields at different flow rates in both qualitative and quantitative manners. This work can enhance the understanding of turbulence generation mechanism, transport behavior, and development characteristics in rotor-stator interaction in vaned radial diffuser pumps.

Analysis of Unsteady Flow in a Radial Diffuser Pump

Three-dimensional, unsteady Reynolds-averaged Navier-Stokes equations are solved by the CFD code CFX-10 in a radial diffuser pump. The turbulence is simulated by the k- ɛ based shear stress transport turbulence model. To validate the CFD results, two-dimensional Laser Doppler Velocimetry (LDV) measurements have also been conducted. Both the phase-averaged velocity field and the turbulence field have been analyzed in detail. A comparison of the phase averaged velocity fields at the radial gap for both methods shows a very good agreement for the global periodic flow field. The analysis shows that a jet-wake structure is observed near the impeller outlet, and the diffuser flow strongly depends on the relative impeller positions which provide different inflow conditions for the downstream diffuser. The effects from the impeller rotation to the diffuser flow become very small at the diffuser outlet.