Rotating Stall Behavior in a Diffuser of Mixed Flow Pump and Its Suppression

2008 ◽  
Author(s):  
Masahiro Miyabe ◽  
Akinori Furukawa ◽  
Hideaki Maeda ◽  
Isamu Umeki
Keyword(s):  
Flow Rate ◽  
Internal Flow ◽  
Rotating Stall ◽  
Low Energy ◽  
Suction Surface ◽  
Mixed Flow ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Pump Design ◽  
Flow Pump

The relationship between pump characteristic instability and internal flow was investigated on a mixed flow pump with specific speed ωs = 1.72 (dimensionless) or 700 (m3/min, m, min−1) by using a commercial CFD code and a dynamic PIV (DPIV) measurement. As a result, it was clarified that the diffuser rotating stalls causes the positive slope of a head-flow characteristic and the backflow at hub-side of the vaned diffuser plays an important role on the onset of the diffuser rotating stall. The complex behaviors of diffuser rotating stall were visualized by the DPIV measurements and CFD simulation. Moreover, the internal flow was investigated in detail and the inception of characteristic instability was presumed as follows: At the partial flow rate, low energy fluids are accumulated in the corner between the hub surface and the suction surface of the diffuser vane. As the flow rate is further decreased, the low energy fluids region at the corner axi-symmetrically expands along the hub and become unstable due to adverse pressure gradient. Then, strong backflow occurs and impinges against passage flow from the impeller at the inlet of the vaned diffuser. In addition, the backflow blocks the passage flow from impeller and the inlet flow angle at the leading edge of adjacent diffuser vane is reduced. Therefore, flow separation occurs near the inlet of suction surface of the vaned diffuser, and a strong vortex is generated there. After that, the vortex develops and becomes a stall core. Based on above considerations, pump design parameter studies were numerically carried out and diffuser rotating stall was suppressed and pump characteristic instability was controlled by enlarging the inlet diameter of diffuser hub.

Investigation of Internal Flow and Characteristic Instability of a Mixed Flow Pump

2009 ◽  
Author(s):  
Masahiro Miyabe ◽  
Akinori Furukawa ◽  
Hideaki Maeda ◽  
Isamu Umeki
Keyword(s):  
Flow Rate ◽  
Internal Flow ◽  
Rotating Stall ◽  
Leakage Flow ◽  
Suction Surface ◽  
Mixed Flow ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Pressure Surface ◽  
Flow Pump

The relationship between pump characteristic instabilities and internal flow was investigated in a mixed flow pump with specific speed of 700 (min−1 m3/min, m) or 1.72 (non-dimensional) by using a commercial CFD code and a dynamic PIV (DPIV) measurement. This pump has two positive slopes of a head-flow characteristic at the flow rates of about 60%Qopt and 82%Qopt. In the authors’ previous study, it was clarified that the characteristic instability at 82%Qopt is caused by the diffuser rotating stall (DRS) and the backflow near the hub of the vaned diffuser plays an important role on the onset of the diffuser rotating stall. In the present paper, the investigation is focused on the instability at about 60% Qopt. Based on both of experimental and numerical results, it was clarified that the characteristic instability at 60%Qopt is caused by the backflow at the inlet of the impeller tip and the leakage flow from the impeller pressure surface to the suction surface plays an important role on the onset of the backflow. The behaviors of backflow at the impeller inlet were visualized by the DPIV measurements and CFD simulation. Moreover, internal flow was investigated in detail and the occurrence of characteristic instability is assumed as follows: At the partial flow rate, the flow angle at the inlet of the impeller tip decreases and the flow hits the impeller pressure surface. Then, the blade loading at the inlet of impeller tip is increased and the recirculation at the leading edge and the leakage flow rate from pressure surface to suction surface increases. The leakage flow causes to generate vortices at the inlet of the suction surface of the impeller. As the flow rate is further decreased, the vortices develop to backflow with swirl. The leakage flow has peripheral component of absolute velocity and the swirling energy is continuously supplied by the backflow. Therefore, even the passage flow at the inlet of the impeller has been getting pre-swirling. The theoretical head, the Euler head is decreased due to the pre-swirling. Moreover, based on the CFD results, the pre-swirling and unsteady vortices near the suction surface of the impeller causes pump characteristic instability. When the flow rate is decreased further more, total head rises because the flow pattern in the impeller changes to centrifugal type due to the backflow from the vaned diffuser at the hub region.

Influence of tip leakage flow and inlet distortion flow on a mixed-flow pump with different tip clearances within the stall condition

2019 ◽  
Vol 234 (4) ◽  
pp. 433-453 ◽  
Author(s):  
Leilei Ji ◽  
Wei Li ◽  
Weidong Shi
Keyword(s):  
Internal Flow ◽  
Energy Performance ◽  
Rotating Stall ◽  
Design Flow ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Mixed Flow ◽  
Tip Leakage ◽  
Flow Pump

In order to investigate the effect of impeller tip clearance on internal flow fields and the rotating stall inception impacted by tip leakage vortex and inlet unsteady flow in a mixed-flow pump, mixed-flow pump models with tip clearances of 0.5 mm, 0.8 mm, and 1.1 mm were numerically calculated, and then the energy performance curves and internal flow structures were obtained and compared. The results show that the pump efficiency and the internal flow fields of numerical calculation are in good agreement with experimental results at design flow rate and near-stall condition. A portion of the positive slope segment appears in the energy performance curves under different tip clearances. The lowest head of the mixed-flow pump in the positive slope region decreases with the increase of the tip clearance while the highest head shows an opposite situation indicating that mixed-flow pumps are easier to stall under small tip clearance. At the design flow rate condition, the tip leakage vortex is relatively stable under different tip clearances and appears as a “snail shell” shape, whereas in rotating stall conditions, the “snail shell” shape disappear and the tip leakage flow on blade front forms a “flat” vortex structure. The inlet swirl flow not only affects the tip leakage flow in rotating stall conditions under different tip clearances, but also blocks the fluid from the inlet pipe. Under the circumstance of the same tip clearance, the main frequency amplitude of pressure pulsation coefficient gradually shifts away from blade passing frequency (96.67 Hz) to the axial frequency (24.17 Hz) when the pump operates in the stall condition.

Effect of Tip Clearance on Rotating Stall in a Mixed-Flow Pump

2019 ◽  
Author(s):  
Wei Li ◽  
Ramesh K. Agarwal ◽  
Ling Zhou ◽  
Enda Li ◽  
Leilei Ji
Keyword(s):  
Flow Separation ◽  
Internal Flow ◽  
Energy Performance ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Pump Efficiency ◽  
Mixed Flow ◽  
Performance Curves ◽  
Flow Pump

Abstract The non-uniform disturbance in the circumferential direction is the main cause for the occurrence of rotating stall in turbomachinery. In order to study the effect of tip clearance leakage flow on rotating stall, the mixed-flow pump models with different tip clearances are numerically simulated, and then the energy performance curves and internal flow structures are obtained and compared. The results show that the computed pump efficiency and the internal flow field of the pump from numerical simulation are in good agreement with the experimental results. A saddle region appears in the energy performance curves of the three tip clearances, and with decrease in tip clearance, the head and efficiency of the mixed-flow pump increase and the critical stall point shifts, and the stable operating range of the mixed-flow pump decreases, which indicates that the mixed-flow pump stalls easily for smaller tip clearance. Under the deep stall condition, the influence of the leakage flow in the end wall area increases gradually with decrease in clearance. For small clearance, the leakage flow moves away from the suction surface to some distance to form a number of leakage vortex strips with the mainstream flow and flows over the leading edge of the next blade and then flows downstream into different flow passages, generating backflow and secondary flow separation at the blade inlet, which seriously damages the spatial structure of the inlet flow. This results in the earlier occurrence of stall. With increase in clearance, the leakage vortex develops along the radial direction towards the middle of the flow channel and large flow separation occurs in the downstream channel, which induces deep stall. For 0.8mm clearance, the whole impeller outlet passage is almost blocked by the backflow of the guide vane inlet, and a deep stall is induced.

Effect of Tip Clearance on Rotating Stall in A Mixed-Flow Pump

2021 ◽  
pp. 1-39
Author(s):  
Wei Li ◽  
Leilei Ji ◽  
Enda Li ◽  
Ling Zhou ◽  
Ramesh Agarwal
Keyword(s):  
Flow Separation ◽  
Internal Flow ◽  
Energy Performance ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Pump Efficiency ◽  
Mixed Flow ◽  
Performance Curves ◽  
Flow Pump

Abstract The non-uniform disturbance in circumferential direction is main cause for occurrence of rotating stall in turbomachinery. In order to study the effect of tip clearance leakage flow on rotating stall, mixed-flow pump models with different tip clearances are simulated and energy performance curves and internal flow structures are obtained and compared. The results show that the computed pump efficiency and the internal flow field of the pump are in good agreement with experimental results. A saddle region appears in energy performance curves of three tip clearances and with decrease in tip clearance, the head and efficiency of mixed-flow pump increase and critical stall point shifts and stable operating range of mixed-flow pump decreases, which indicates that mixed-flow pump stalls easily for smaller tip clearance. Under deep stall condition, influence of leakage flow in end wall area increases gradually with decrease in clearance. For small clearance, the leakage flow moves away from suction surface to some distance to form number of leakage vortex strips with mainstream flow and flows over the leading edge of next blade and then flows downstream into different flow passages generating back flow and secondary flow separation at the blade inlet, which seriously damages the spatial structure of inlet flow. This results in earlier occurrence of stall. With increase in clearance, the leakage vortex develops along radial direction towards middle of flow channel and large flow separation occurs in downstream channel which induces deep stall.

Blade Interaction Forces in a Mixed-Flow Pump With Vaned Diffuser

2009 ◽  
Author(s):  
Cheng Li ◽  
B. P. M. van Esch
Keyword(s):  
Flow Rate ◽  
Mixed Flow ◽  
Interaction Forces ◽  
Vaned Diffuser ◽  
Shaft System ◽  
High Head ◽  
The Many ◽  
Direction Opposite ◽  
Flow Pump ◽  
Good Agreement

Hydrodynamic forces in turbomachinery can cause problems ranging from excessive wear to vibrations. Of the many different causes of fluid-induced forces, their source attributed to blade interaction is perhaps best studied. Most studies, however, focus on high head pumps. This paper presents a study of blade interaction forces in a mixed-flow pump with vaned diffuser. It covers both experimental and numerical results. A mixed-flow pump is built into a closed-loop test rig. In order to measure the instantaneous forces and bending moments on the impeller, a co-rotating dynamometer is used, which is built in-between the impeller and the shaft of the pump. Extensive calibration proved necessary to determine the dynamic behavior of the shaft system. Measurements of forces at blade passing frequency show an unexpected dependency on flow rate. Another important observation is that blade excitation forces cause the impeller to whirl in a direction opposite to shaft rotation. Results of measurements are compared with unsteady CFD calculations using FLUENT®. Computed global characteristics show a good agreement with measurements. Also the magnitude of blade interaction forces shows a good qualitative agreement. Over a large range of flow rates, the dependency of magnitude on flow rate agrees well with the trend found in the measurements. Deviations are explained.

Numerical and Experimental Study of Inner Flow and Hydraulic Performance of the Mixed-Flow Pump With Low Specific Speed

2018 ◽  
Author(s):  
Jianping Yuan ◽  
Meng Fan ◽  
Yanjun Li ◽  
Yanxia Fu ◽  
Rong Lu
Keyword(s):  
Rapid Development ◽  
Internal Flow ◽  
Fluctuation Analysis ◽  
Market Demand ◽  
Mixed Flow ◽  
Pump Design ◽  
Flow Rates ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Flow Pump

Mixed flow pumps are very suitable for market demand with the rapid development of urbanization, especially for low specific speed mixed flow pumps which has been widely used in various fields [1–3]. In this study, the calculations of the incompressible 3D internal flow of the mixed-flow pump with low specific speed was carried out by using CFD technique based on the N-S equation coupled with the standard k-ε turbulence model at different flow rates. The hydraulic performances of the mixed-flow pump as well as the inner flow were analyzed in comparison with the corresponding experimental data. Meanwhile, the static pressure and relative velocity distribution on blades were studied at low, design as well as large flow rates, respectively. Finally, it can obtain that the predicted pump performance curves based on numerical simulation have a good agreement with the experimental results, which verify the numerical method applied in this work accurate in a certain extent. Furthermore, the results also provide some references to hydraulic forces and pressure fluctuation analysis and the performance improvement for the mixed-flow pump design.

Internal Flow Mechanism of Axial-Flow Pump With Adjustable Guide Vanes

2013 ◽  
Author(s):  
Honggeng Zhu ◽  
Rentian Zhang ◽  
Bin Xi ◽  
Dapeng Hu
Keyword(s):  
Flow Rate ◽  
Axial Flow ◽  
Internal Flow ◽  
Flow Angle ◽  
Guide Vanes ◽  
Setting Angle ◽  
Pumping Efficiency ◽  
Outlet Flow ◽  
Axial Flow Pump ◽  
Flow Pump

Axial-flow pumps are widely used in many fields where low pumping head and large flow rate are required such as irrigation and drainage, flood control, bio-environmental protection and inter-basin water diversion. Conventional axial-flow pump diffuser is designed with post fixed guide vanes to eliminate circulation, diffuse water and decrease flow velocity while converting dynamic energy to pressure energy. Under designed flow rate the inlet setting angle of the fixed guide vanes is designed to be equal to the outlet flow angle of the impeller blades which is regarded to be the best operating condition. Under off-design conditions the outlet flow angle of the impeller blades does not match the inlet setting angle of guide vanes any more. As a result hydraulic losses are increased, flow separation appeared and vortex generated inside the diffuser, the operation conditions of pump is deteriorated, bringing in bad cavitation characteristics, more energy consumption and lower pumping efficiency. The proposal of Axial-flow pumps with adjustable guide vanes are put forward in this paper, in which the inlet setting angle of guide vanes can be adjusted to coordinate with the change of flow rate and impeller blade setting angle and guarantee the outlet flow angle of impeller blades matching the inlet setting angle of guide vanes. The three-dimensional time-averaged N-S equations, closed by the standard κ–ε turbulence model, are adopted to simulate the internal flow fields of axial-flow pumps with fixed and adjustable guide vanes, and their performances are predicted. The internal flow mechanism of an axial-flow pump with adjustable guide vanes is investigated, and computational fluid dynamics is adopted to simulate and analyze the internal flow fields. Computation results indicate that the value of the highest pumping efficiency is slight changed while the vane setting angle is adjusted when the inlet setting angles of blades are fixed and the setting angles of guide vanes are regulated. Under off-design conditions the flow conditions inside the diffuser of axial-flow pump with adjustable guide vanes can be improved, the hydraulic loss reduced and the pumping efficiency can be raised effectively.

Numerical investigation on the unstable flow at off-design condition in a mixed-flow pump

2019 ◽  
Vol 233 (7) ◽  
pp. 849-865 ◽  
Author(s):  
Yongfei Yang ◽  
Wei Li ◽  
Weidong Shi ◽  
Yuanfeng Ping ◽  
Yang Yang ◽  
...  
Keyword(s):  
Flow Rate ◽  
Pressure Fluctuation ◽  
Guide Vane ◽  
Dominant Frequency ◽  
Rotating Stall ◽  
Unstable Flow ◽  
Mixed Flow ◽  
Propagation Process ◽  
Stall Inception ◽  
Flow Pump

The mixed-flow pump is wildly used in industrial and agricultural fields, and the requirements for its stability become more and more restricted with the improvement of the capacities. When the pump is operated under part-loading conditions, unstable characteristic like rotating stall happens and brings intensive vibration and noise. To reveal the internal unstable flow characteristics in mixed-flow pump, unsteady numerical simulation is conducted under different flow rates in the current research. The secondary flow and the vortex induced by the unsteady flow in the pump, which vary with the change of the flow rate, are analyzed according to the simulation results. Pressure fluctuation in different parts of the impeller is numerically predicted and correlated to the rotating stall propagation process. With the reduction of the flow discharge, a critical flow rate (0.6 Qdes in the current model pump) is found related to the rotating stall inception. Unstable vortex structure is found in part of the flow passages of the impeller under the stall inception stage; 0.56 Qdes is the flow rate related to the deep rotating stall under which stable stall vortexes are found in each flow passage of the impeller. Three types of pressure fluctuation characteristics representing different flow field pattern in the impeller are found. When the pump is working at designed flow rate, the pressure fluctuation is regular with the dominant frequency being the rotation frequency fs of the rotor. At the stall inception condition, when the stall core appears in the flow passages of the impeller in turn, the amplitude of the pressure fluctuation is increased and the dominant frequency is changed to a low-frequency signal. When the flow rate is reduced below deep stall condition, owning to the reflux from the guide vane and the intensive rotor–stator interaction, the blade passing frequency of the guide vane fb2 becomes the dominant frequency. Finally, unsteady characteristics of the flow field under stall inception condition are analyzed to demonstrate the propagation process of the rotating stall. The stall vortex is found to propagate from the stalled flow passage to the next, through the tip area of the blade leading edge. During the propagation process, the first vortex shrinks and disappears gradually, while the second vortex grows continuously, and the third vortex shows up at the vanishment of the first stall vortex. This research provides detailed information for the unstable flow especially related to rotating stall evolution with the variation of the operating flow rate of the mixed-flow pump with guide vane.

Surge in a Low-Speed Radial Compressor

1998 ◽  
Author(s):  
Corine Meuleman ◽  
Frank Willems ◽  
Rick de Lange ◽  
Bram de Jager
Keyword(s):  
Flow Rate ◽  
Pressure Rise ◽  
Flow Coefficient ◽  
Lumped Parameter Model ◽  
Pressure Oscillations ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Radial Compressor ◽  
Low Speed ◽  
Lumped Parameter

Surge is measured in a low-speed radial compressor with a vaned diffuser. For this system, the flow coefficient at surge is determined. This coefficient is a measure for the inducer inlet flow angle and is found to increase with increasing rotational speed. Moreover, the frequency and amplitude of the pressure oscillations during fully-developed surge are compared with results obtained with the Greitzer lumped parameter model. The measured surge frequency increases when the compressor mass flow is throttled to a smaller flow rate. Simulations show that the Greitzer model describes this relation reasonably well except for low rotational speeds. The predicted amplitude of the pressure rise oscillations is approximately two times too small when deep surge is met in the simulations. For classic surge, the agreement is worse. The amplitude is found to depend strongly on the shape of the compressor and throttle characteristic, which are not accurately known.

Effect of Blade Thickness on Rotating Stall of Mixed-Flow Pump Using Entropy Generation Analysis

Energy ◽  
2021 ◽  
pp. 121381
Author(s):  
Leilei Ji ◽  
Wei Li ◽  
Weidong Shi ◽  
Fei Tian ◽  
Ramesh Agarwal
Keyword(s):  
Entropy Generation ◽  
Rotating Stall ◽  
Mixed Flow ◽  
Blade Thickness ◽  
Flow Pump
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