scholarly journals Effect of Splitter Blades on Performances of a Very Low Specific Speed Pump

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3785
Author(s):  
Lilian Chabannes ◽  
David Štefan ◽  
Pavel Rudolf
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Detailed Analysis ◽  
Performance Characteristics ◽  
Absolute Velocity ◽  
Numerical Studies ◽  
Impeller Outlet ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Average Wall Shear Stress

The usage of splitter blades to enhance the performances of low specific speed pumps is common practice. Based on experimental and numerical studies, the influence of the addition of one and two splitter blades is investigated on a very low specific speed pump to assess their impact not only on the performance characteristics but also on the losses in all pump domains. First, the main characteristic curves are discussed and it is shown that the usage of splitter blades enhances the head of the pump while not impairing its efficiency. Secondly, a detailed analysis of the losses in the pump reveals that splitter blades improve the flow in all parts of the pumps, but the volute. The flow at the impeller outlet shows that splitter blades largely benefit the slip factor and discharges a more blade-congruent flow in the volute. However, higher absolute velocity at the outlet of the impeller with splitter blades increases friction at the volute wall, as confirmed by the average wall shear stress in the different tested cases.

Effect of the Broken Rib Locations on the Heat Transfer and Fluid Flow in a Rotating Latticework Duct

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Wei Du ◽  
Lei Luo ◽  
Songtao Wang ◽  
Jian Liu ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Nusselt Number ◽  
Wall Shear Stress ◽  
Flow Structure ◽  
Suction Side ◽  
Spiral Flow ◽  
Numerical Studies ◽  
Rotational Number ◽  
Wall Shear

AbstractA numerical method was used to study the effect of the broken rib locations on the heat transfer and flow structure in the latticework duct with various rotational numbers. The latticework duct had eleven subchannels on both the pressure side and the suction side. The crossing angle for each subchannel was 45 deg. The numerical studies were conducted with five different broken rib locations and six rotational numbers (0–0.5). The Reynolds number was fixed as 44,000. The flow structure, wall shear stress, and Nusselt number distributions were analyzed. It was found that the upward spiral flow and helical flow dominated the flow structure in the latticework duct. In addition, the impingement region (at the beginning of the subchannel) induced by the upward spiral flow was responsible for the high Nusselt number and wall shear stress. After adoption of the broken rib in the latticework duct, the Nusselt number was increased by 6.12% on the pressure endwall surface and increased by 6.02% on the rib surface compared to the traditional latticework duct. As the rotational number was increased, the Nusselt number on the pressure endwall surface was decreased by up to 5.4%. However, the high rotational number enhanced the heat transfer on the suction side. The high rotational number also decreased the friction factor in the latticework duct. Furthermore, the overall thermal performance was increased by 12.12% after adoption of the broken ribs on both the turn region and the impingement region.

scholarly journals Preliminary Computational Hemodynamics Study of Double Aortic Aneurysms under Multistage Surgical Procedures: An Idealised Model Study

2013 ◽  
Vol 2013 ◽  
pp. 1-9
Author(s):  
Yosuke Otsuki ◽  
Nhat Bui Minh ◽  
Hiroshi Ohtake ◽  
Go Watanabe ◽  
Teruo Matsuzawa
Keyword(s):  
Shear Stress ◽  
Aortic Aneurysm ◽  
Wall Shear Stress ◽  
Aortic Aneurysms ◽  
Average Pressure ◽  
Navier Stokes Equation ◽  
Staged Surgery ◽  
Continuity Equations ◽  
Wall Shear ◽  
Average Wall Shear Stress

Double aortic aneurysm (DAA) falls under the category of multiple aortic aneurysms. Repair is generally done through staged surgery due to low invasiveness. In this approach, one aneurysm is cured per operation. Therefore, two operations are required for DAA. However, post-first-surgery rupture cases have been reported. Although the problems involved with managing staged surgery have been discussed for more than 30 years, investigation from a hemodynamic perspective has not been attempted. Hence, this is the first computational fluid dynamics approach to the DAA problem. Three idealized geometries were prepared: presurgery, thoracic aortic aneurysm (TAA) cured, and abdominal aortic aneurysm (AAA) cured. By applying identical boundary conditions for flow rate and pressure, the Navier-Stokes equation and continuity equations were solved under the Newtonian fluid assumption. Average pressure in TAA was increased by AAA repair. On the other hand, average pressure in AAA was decreased after TAA repair. Average wall shear stress was decreased at the peak in post-first-surgery models. However, the wave profile of TAA average wall shear stress was changed in the late systole phase after AAA repair. Since the average wall shear stress in the post-first-surgery models decreased and pressure at TAA after AAA repair increased, the TAA might be treated first to prevent rupture.

scholarly journals Comparison of energy parameters of a centrifugal pump with a multi-piped impeller in cooperation either with an annular channel and a spiral channel

2018 ◽  
Vol 8 (1) ◽  
pp. 513-522 ◽  
Author(s):  
Bartłomiej Chomiuk ◽  
Janusz Skrzypacz
Keyword(s):  
Centrifugal Pump ◽  
Annular Channel ◽  
Operating Parameters ◽  
Centrifugal Pumps ◽  
Impeller Outlet ◽  
Flow Geometry ◽  
Quantitative Verification ◽  
Flow Through ◽  
Low Specific Speed ◽  
Specific Speed

Abstract The article presents results of numerical analyzes, which raise a subject of influence of the cooperation the multi-piped impeller with a rationalized flow geometry of annular casing and volute casing for liquid flow through centrifugal pump and their operating parameters in the extremely low specific speed nq<10. The multi-piped impeller (patented by authors) is a major alternative to classic vane impellers. The stator type is responsible for the conversion of the kinetic energy of the liquid by the impeller outlet into potential energy, which determines the overall efficiency of the pump. Also, the article presents qualitative and quantitative verification of results obtained by computer modeling and an attempt to estimate their accuracy. The article focuses mainly on the comparison of the performance parameters of the pump with a multi-piped impeller in cooperation with two stator types with a rationalized flow geometry. Both outlet elements were tested in various configurations of constructional features. The complexity of the construction of the stator can significantly affect the manufacturing costs of pump unit. Knowledge concerning construction of hydraulic elements of centrifugal pumps working in the range of parameters corresponding specific speed (nq<10) is insufficient. As shown in the paper, the annular type casing model pump cooperating with a multi-piped impeller, designed in accordance with literature, reached far poorer operating parameters than the rational annular construction in a configuration with the same impeller.

Effect of the Section Area of Volute in Low Specific Speed Centrifugal Pumps on Hydraulic Performance

2009 ◽  
Author(s):  
Xiang Zhang ◽  
Yang Wang ◽  
Jianhui Fu ◽  
Cui Dai ◽  
Caihong Wang
Keyword(s):  
Flow Rate ◽  
Low Flow ◽  
Centrifugal Pumps ◽  
Blade Angle ◽  
Rate Condition ◽  
Section Area ◽  
Impeller Outlet ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Experimental Researches

The volute of low specific speed centrifugal pumps has a great impact on the performance of the pump in that the highest efficiency can only be achieved when the impeller is matched with a well-designed volute. At off-BEP conditions, the performance of pumps declines as a consequence of a mismatch between characteristics of the impeller and the volute. The section area is the most important factor of volute. Numerical simulations and experimental researches have been carried out on the routine-designed impeller and the non-overloading designed impeller (different impeller outlet blade angle between two types of impellers) in the hope of finding out the effect of the section area of volute on low specific speed centrifugal pumps. It has been found that the uneven flow rate on different volute sections caused by the backflow between volute and impeller is one of the reasons for the efficiency decline of pumps at off-BEP conditions, especially in the low flow rate condition. It has also been found that the routine-designed impeller is more easily affected by the section area of volute than non-overloading designed impeller.

Measurement of the Periodic Flow Field in a Radial Diffuser Pump by the PIV-Method

2007 ◽  
Author(s):  
Friedrich-Karl Benra ◽  
Jianjun Feng ◽  
Hans Josef Dohmen
Keyword(s):  
Particle Image ◽  
Flow Measurements ◽  
Piv Method ◽  
Diffuser Flow ◽  
Image Velocimetry ◽  
Impeller Outlet ◽  
Rear Part ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Inflow Conditions

Detailed flow measurements are conducted by two-dimensional Particle Image Velocimetry (PIV) in a low specific speed radial diffuser pump at the design operating point, in order to investigate the impeller-diffuser interaction. The measurements are conducted at midspan for different relative positions between the impeller and diffuser. The measuring region covers a complete impeller channel and also a complete diffuser channel. The analysis of the experimental results shows that a jet-wake structure is observed near the impeller outlet. The presence of the diffuser vanes mainly affects the impeller flow at the rear part near the impeller outlet. The diffuser flow strongly depends on the relative impeller position which provides different inflow conditions for the diffuser.

A New Probe for Measurement of Velocity and Wall Shear Stress in Unsteady, Reversing Flow

1981 ◽  
Vol 103 (3) ◽  
pp. 478-482 ◽  
Author(s):  
R. V. Westphal ◽  
J. K. Eaton ◽  
J. P. Johnston
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Turbulent Flows ◽  
Solid Wall ◽  
Flow Direction ◽  
Streamwise Velocity ◽  
Tracer Technique ◽  
Wall Shear ◽  
Initial Results ◽  
Average Wall Shear Stress

Separated turbulent flows exhibit instantaneous reversals of flow direction which make measurement of the velocity field extremely difficult. A three-wire heat-tracer technique has been employed to measure streamwise velocity of a low-speed air flow very near a smooth, solid wall; the wall shear stress is calculated using a similarity hypothesis. Initial results presented show the evolution of average wall shear stress and rms fluctuation intensity of wall shear stress in a reattaching 2-D flow downstream of a backward-facing step.

scholarly journals Effects of the impeller–volute tongue interaction on the internal flow in a low-specific-speed centrifugal pump with splitter blades

2017 ◽  
Vol 232 (2) ◽  
pp. 170-180 ◽  
Author(s):  
Yandong Gu ◽  
Shouqi Yuan ◽  
Ji Pei ◽  
Jinfeng Zhang ◽  
Fan Zhang ◽  
...  
Keyword(s):  
Energy Loss ◽  
Centrifugal Pump ◽  
Time History ◽  
Internal Flow ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Impeller Outlet ◽  
Pressure Peak ◽  
Low Specific Speed ◽  
Specific Speed

To investigate the effects of the main blades and splitter blades interacting with the volute tongue on the internal flow in a low-specific-speed centrifugal pump, the Reynolds-averaged Navier–Stokes equation, coupled with SST k-ω turbulence model, is employed to simulate the transient turbulent flow in the whole flow passage. The numerical simulation results have been verified with the experimental measurements by comparing the head and efficiency. The pressure fluctuation caused by impeller–volute tongue interaction, including time–history and frequency characteristics, is calculated and analyzed at five monitoring points adjoining the impeller outlet and tongue, as well as the torque of a single main blade and a single splitter blade. After that, both the energy loss and vorticity distributions on the middle section are discussed when the impeller rotates to four circumferential positions relative to the cutwater. The results show that the maximum pressures at the monitoring points occur before the blades reach the closest circumferential position with respect to the cutwater, and the peak pressure near the trailing edge of splitter blades is larger than main blades. There is only one torque peak of a single blade in one revolution when the angle between the monitoring blade and tongue is about 15°. Additionally, the torque peak arises before the torque valley, but the pressure valley at monitoring points in the impeller comes earlier than the pressure peak. Both the energy loss and vorticity are enlarged around the volute tongue evidently after the blades pass by the cutwater, and the splitter blades produce more unsteadiness and energy dissipation than main blades.

Unsteady Flow in the Vaned Diffuser of a Low Specific Speed Centrifugal Pump With an Unshrouded Impeller

2019 ◽  
Author(s):  
Asuma Ichinose ◽  
Tomoki Takeda ◽  
Kazuyoshi Miyagawa ◽  
Yohei Ogawa ◽  
Hideyo Negishi ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
Internal Flow ◽  
The Other ◽  
Vaned Diffuser ◽  
Design Point ◽  
Other Hand ◽  
Impeller Outlet ◽  
Outlet Flow ◽  
Low Specific Speed ◽  
Specific Speed

Abstract The unsteady internal flow in a low specific speed centrifugal pump was experimentally and numerically investigated. Unshrouded impellers enable high head designs but on the other hand, they exhibit complicated internal flow and an efficiency decline compared to shrouded impellers. Furthermore, the complicated impeller outlet flow induces unsteady internal flow in the vaned diffuser. Therefore, a detailed investigation of the internal flow is required in order to increase the efficiency of these low specific speed centrifugal pumps. The aims of this paper are to clarify the loss mechanisms in the impeller and to investigate the effect of impeller outlet flow to the diffuser internal flow at the design point. The detailed pump internal flow is investigated using unsteady computation, which enables the computation of the 3D flow pattern. The reversed flow and the secondary flow are induced by the tip leakage flow, and this creates a high loss region in the blade-to-blade region. On the other hand, the mixing effect is remarkable at the impeller outlet, and this affects the creation of the wake. This flow behavior makes the internal flow of the diffuser unsteady and the diffuser performance fluctuates due to the impeller wake at the design point.

Simulation analysis of aneurysm embolization surgery: Hemorheology of aneurysms with different embolization rates (CTA)

2021 ◽  
pp. 1-14
Author(s):  
Quan Bao ◽  
Xin Meng ◽  
Mingcheng Hu ◽  
Jian Xing ◽  
Dan Jin ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Cerebral Aneurysm ◽  
Endovascular Embolization ◽  
Oscillatory Shear ◽  
Oscillatory Shear Index ◽  
Aneurysm Embolization ◽  
Time Average ◽  
Wall Shear ◽  
Average Wall Shear Stress

BACKGROUND: Embolization degree acts as an important factor affecting recurrence of aneurysm. OBJECTIVE: To analyze the role of hemodynamics parameters of different degrees of embolization in the occurrence, development and post-treatment of aneurysms, and to determine the specific factors causing the occurrence and recurrence of aneurysms after hemodynamics treatment. Our study provides a theoretical basis for the prevention and treatment of aneurysms. METHODS: Computed Tomography Angiography (CTA) data of a patient with cerebral aneurysm were used to model 0%, 24%, 52%, 84% and 100% of endovascular embolization, respectively. The time average wall shear stress, time average wall shear stress, oscillatory shear index, hemodynamics formation index and relative retentive time were used to analyze the changes of hemodynamics indexes in different embolic models. RESULTS: With the increase of embolic rate, the values of time average wall shear stress, time average wall shear stress grade and aneurysm index formation gradually increased, and the values of relative retention time gradually decreased. Oscillatory shear index was higher in patients with incomplete embolization and decreased in patients with complete embolization. CONCLUSIONS: As the degree of embolization increased, the blood flow tended to stabilize, reducing the risk of cerebral aneurysm rupture, and finding that the wall of the vessel junction was susceptible to injury.

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