Can Kang

Comparison Study of a Vertical-Axis Spiral Rotor and a Conventional Savonius Rotor

A vertical-axis spiral rotor with two end plates and one middle plate was proposed for achieving a high wind energy transfer efficiency. Computational fluid dynamics (CFD) technology was adopted to evaluate the performance of the spiral rotor. Three-dimensional flow simulation was conducted by using Spalart-Allmaras one-equation turbulence model. Comparison of the spiral rotor with a conventional Savonius rotor was performed. Flow characteristics around the two rotors were analyzed to illustrate the correlation between flow and rotor performance. The study indicates that torque performance of the spiral rotor is more favorable during its whole rotation cycle. When maximum torque coefficient is generated, large pressure difference can be found between the convex and concave side of the blade. Oppositely, the minimum static coefficient is accompanied by indistinctive pressure difference and large-scale boundary layer separation zones.

Analysis on Turbulent Flow in the Impeller of Chemical Pump

To study the phenomena of two-phase flow with salt crystallizing in the chemical pump, the 3-D turbulent flow in the impeller of chemical pump was simulated under the condition of rinsing. The internal flow between the impellers of 1H65 chemical pump was investigated. Based on the Reynoldsaveraging N-S equations and the standard k -ɛ two equations turbulent model, the simulations of turbulent flow between the impellers are performed by using the flow computing software Fluent under different operating conditions. The calculation results are compared with the experimental data by particle image velocimetry (PIV). Based on the analysis of the calculated results of velocity and pressure profiles in the chemical pump and experimentally observed phenomenon of flow impact, secondary flow and recirculation, some design improvements are proposed, which give suggestions on the optimal design and internal two-phase flow study of the chemical pump.

Experiment and Performance Evaluation of a New Vertical-axis Spiral Rotor

To evaluate the performance parameter of a new vertical-axis spiral wind rotor with two end plates and a middle plate, an experiment was carried out by using a low-speed circulation wind tunnel. The tested rotor has a height of 400 mm and rotor diameter of 136 mm. Under two conditions of with and without central shaft, no-load rotation speed, static torque coefficient and power output at different air velocities were measured. The results indicate that the tested rotor has good and stable operation property. The static torque coefficient under condition of with central shaft is more satisfying than that under condition of without central shaft. When air velocity ranges from 10 m/s to 15 m/s, wind energy utilization ratio distributes smoothly with comparatively high values under the condition of with central shaft.

Statistical Characteristics in Water Jet Discharged From a Central-Body Nozzle

As a special nozzle, central-body nozzle has attracted a lot of attention since its concept was proposed in 1980s. With Karman vortex street principle and phase-change theory, cavitation is expected to occur just after the central body. However, turbulent features in water jet flow discharged from central-body nozzle have not been illustrated by sufficient experimental data when water is ejected into ambient air. Under jet pressures of 11MPa, 13MPa and 17MPa, free water jet discharged from a central-body nozzle was experimentally studied. Phase Doppler particle anemometry (PDPA) was applied to measure non-intrusively the flow fields. Four traverse sections were selected for data visualization and representative description of the flow features. Control volumes at center and rim of the four sections were monitored for recording of every validated single droplet passing through. Experiment results indicate that pressure increase influences maximum velocity significantly. Obvious statistical characteristics exist at jet center and jet rim. The statistical feature of the droplet distribution varies slightly with pressure increase. Turbulent fluctuation is proved to be in reasonable relation to droplet behavior and droplet diameter distribution.Copyright

Cavitation Analysis Near Blade Leading Edge of an Axial-Flow Pump

In an axial-flow impeller, rotating flow with cavitation is simulated and experimentally studied with high speed photography technique. Special attention is paid to cavitation profile and its evolution near the blade leading edge. Flow field is firstly computed without cavitation model and low-pressure area is defined, then with cavitation model, the cavity volume fraction distributions are obtained. With corresponding model pump and a test rig, cavitation near blade leading edge is recorded with high-speed photography technique. Observed cavity profile and cavitation inception location are both in good accordance with that obtained through simulation. Cavity movement from suction surface to pressure surface through blade tip is also analyzed.

Research on Cavitation Induced Noise in a Centrifugal Pump

To study the cavitation flow field and cavitation induced noise features in a centrifugal pump, a model pump is chosen as the research object. Cavitation flow field at design and off-design operating conditions is visualized by high speed camera. The cavitation bubbles spatial distribution changing with pump net positive suction head (NPSH) value have been captured. Meanwhile, cavitation noise signals from the pump at the corresponding operating conditions have been acquired in the frequency band from 10 up to 8kHz. Noise levels at broadband frequency and discrete frequency, such as rotating frequency (RF) and blade pass frequency (BPF), are discussed. It is of help to recognize the relationship between cavitation bubbles and emitted noise spectrum characteristics. Experimental results indicate that the total noise level is unlikely to raise before and in the cavitation inception period. But sound pressure level (SPL) over high frequency broadband increases obviously, as well as SPL at BPF and half of that. It is hard to change at RF. When the NPSH goes down until to the onset of cavitation damage, cavitation cloud appears. The volume fraction of bubbles in every impeller passage is different. The total and high frequency noise level reach peak values near the NPSH critical point. The discrete tone at half of BPF also raises steeply. Cavitation bubbles are filled both on suction and pressure side of the blades in fully developed cavitation stage. Emitted noise energy fluctuates due to the unsteady features of internal flow in the pump.Copyright

Characteristics of Impinging Water Jet Discharged From a Central-Body Nozzle

Submerged water jet discharged from a central-body nozzle was investigated through flow visualization, numerical simulation and impingement experiment. Under jet pressure of 15 MPa, three layout plans of central body were introduced and corresponding water jets were visualized by using high speed photography technique. Cavitating jet flow fields were simulated with commercial computational fluid dynamics (CFD) software Fluent which employs full cavitation model. Sandstone cuboid was used as the sample workpiece exposed to the submerged water jet of 15MPa. It is proved that cavitation tone exist in the wake flow after the central body. When the end cross-section of the central body is parallel with the nozzle outlet section, the largest axial length of cavitation zone is obtained. Compared with round water jet with the same equivalent nozzle outlet area, the central-body nozzle yields stronger impinging effect.Copyright

Experimental Study on Cavitating Flow in Impeller of Axial-Flow Pump

Based on the external characteristic test, the performance of designed axial-flow model pump was determined. The cavitation performance of model pump at the best efficiency point was confirmed through the cavitation test. The cavitating flows in impeller at different NPSH values were shot by the high speed digital camera. MiVnt image analysis software was utilized to process the shooting images, track the cavitation region and outline of cavitation bubbles cluster. The experimental results show that the incipient cavitation regions are located in the inlet of blade suction surface near the tip and the leading edge of tip airfoil. With the decrease of NPSH values, the cavitation region at tip airfoil moves gradually from leading edge to trailing edge and the type of cavitation is vortex cavitation, its rotation axis direction is the same as circumferential direction. The cavitation region at blade suction surface indicates the same moving trend as at tip airfoil. The emerging of cloudy cavitation at the middle of blade suction surface indicates the beginning of pump cavitation. With the further increase of volume proportion of cavitation bubbles in impeller channel, the pump performance decreases severally. The experimental results reveal the preliminary laws of cavitating flow and provide an effective reference for the cavitation region and development process in impeller of axial-flow pump.Copyright

Influence of Axial Vane on Inner Flow and Performance of a Molten-Salt Pump

A vertically installed two-stage pump transporting molten salt was studied. Axial vane diffuser was designed to relieve the effect of non-uniformity of circumferential pressure distribution near the impeller outlet. Performance test was carried out to evaluate the working ability and acquire the operation performance parameters of the designed pump. Numerical simulation was conducted to capture the variation of main flow parameters with time and space. Both steady and unsteady computations were performed and mediums of water and molten salt were defined in computation for comparative analysis. The results indicate that circumferential pressure distributions at different axial positions exhibit apparently different tendencies. Under the designed flow rate, energy loss in the rotor-stator interaction zone is relatively small, while under the condition of small flow rate, the loss can reach as high as 3.5% of the pump head. With impeller’s rotation, the flow pattern near blade outlet experiences drastic change. Dimension, shape and location of the typical flow structure change accordingly due to the interplay between rotating impeller and stationary axial vane.Copyright

Water Jet Performance Variation for Intrusion of a Cylinder Central-Body

Based on Karman vortex street principle, central-body nozzle is expected to arouse cavitation in the discharged jet and then result in strong impact on acted object. To discover the influence of central-body on flow characteristics, under the same jet pressure of 15MPa, comparison between the two free water jet fields produced respectively by a central-body nozzle and a round nozzle was conducted. Phase Doppler particle anemometry (PDPA) was applied to measure velocity distribution, turbulent fluctuation and droplet diameter distribution at different traverse sections. Experimental results show that although the annular jet tends to concentrate soon after the central body, the radial diffusion of the jet discharged from the central-body nozzle is more obvious. For the two jets kinetic energy is well remained along the jet direction and high-velocity zone is wider near the jet axis of the central-body nozzle. For the jet discharged from the central-body nozzle, turbulent fluctuation near the jet axis is relatively weak. As for possible cavitation, the position is right after the central body and the reachable distance of cavitation effect is short, which produces an inevitable restriction on the nozzle’s application. And similar Sauter mean diameter (SMD) distribution profiles are found in the two jet fields especially when distance between nozzle and traverse section gets large. The study here provides quantitative and comparative information for the two nozzles and can be referred to in further study and optimal design of central-body nozzle.Copyright