Tangential Leakage Research Articles

Analysis of Tangential Leakage Flow Characteristics in a Variable Diameter Dual Circular Arc Vortex Compressor

(1) To address issues such as a low compression ratio and severe leakage in uniform wall thickness vortex compressors, this paper adopts a new scroll compressor model with a variable diameter double arc combined profile, which has a larger pressure ratio and smaller leakage than the scroll compressor with equal wall thickness that can bring new ideas and methods to the research in the field of scroll compressors. (2) This paper determines the theoretical equation of the variable diameter dual circular arc vortex profile and the combined profile, and infers mathematical models for the leakage line length, working chamber volume, and gas leakage per unit rotation angle of the vortex compressor, followed by simulation. (3) The results show that compared to the uniform wall thickness involute profile, the variable diameter dual circular arc combined profile model reduces the leakage line length by 25%, increases the average total pressure at the working chamber outlet by 2.38%, and decreases the leakage amount by 3.2%, consistent with theoretical analysis. (4) The tangential leakage caused by the radial gap in the variable diameter dual circular arc combined profile model has a significant impact on the uneven distribution of temperature and velocity fields in the working chamber of the vortex compressor, but a smaller impact on the pressure field.

Numerical calculation of scroll compressor geometry and assessment of its delivery

This paper proposes innovative numerical methods for calculating the chamber volumes and tangential leakage gaps in a scroll compressor, a critical aspect of enhancing its performance and efficiency. It proposes two methods, namely, moving away from traditional analytical approaches and presenting a 0D model for mass flow delivery at varying rotational frequencies and discharge pressures. The first method utilizes the numerical identification of conjugate points with a minimum distance within the fixed and orbiting involute pair to calculate chamber volumes. This approach compensates for integration errors by considering the subareas defined by the normal distance of each involute to the other. The second method simplifies the process by assuming that the line defining the orbital angle intersects the involutes at the conjugate points, with volumes calculated using area discretization on triangles. Both methods underwent validation against three analytical calculations, showing an agreement within an overall uncertainty error of 3% for the maximum suction volume. The 0D model’s results were compared with Ma et al.'s hybrid method and actual measurements. Upon improving Ma’s model by accounting for intake air heating and negative pressure in the intake volume, a significant agreement between modeling and measurements was observed. This study concludes that the proposed numerical methods can enhance the accuracy of scroll compressor geometry calculation and mass flow delivery, considering the tangential gap.

Investigation on the wet compression performance of a co-rotating scroll hydrogen recirculation pump for fuel cell engine systems

The scroll-type hydrogen recirculation pump is critical for fuel cell vehicle powertrain systems, yet its performance under multiphase conditions remains poorly understood. This study proposes a co-rotating scroll hydrogen pump with array scrolls and investigates its aerodynamic performance, including volumetric efficiency, isentropic efficiency, and power consumption, under varying inlet humidity through 3D transient numerical simulations. Additionally, the effects of operational and geometric parameters (rotational speed, radial clearance, and axial clearance) on the wet compression performance of the pump at the maximum inlet humidity are carried out. Results show that inlet humidity primarily affects the compression and discharge processes of the pump. Increasing inlet humidity suppresses tangential leakage, improving volumetric efficiency, while reducing isentropic efficiency. With inlet humidity increasing from 0% to 100%, the volumetric and isentropic efficiencies change by + 1.84% and −2.3%, respectively, with a power consumption increase of approximately 8.9 W. Higher rotational speeds significantly decrease the isentropic efficiency, while axial clearance has a more pronounced impact on both efficiencies compared to radial clearance. Specifically, increasing rotational speed from 5000 r/min to 15,000 r/min enhances volumetric efficiency by 9.27% and reduces isentropic efficiency by 6.72%. Similarly, increasing radial clearance from 20 μm to 40 μm reduces volumetric efficiency by 5.51% and isentropic efficiency by 0.87%. Raising axial clearance from 20 μm to 40 μm results in a 17.86% drop in volumetric efficiency and 10.7% in isentropic efficiency. These findings offer design insights for high-efficiency co-rotating scroll hydrogen pumps.

Analysis of 3D Transient Flow in a High-Speed Scroll Refrigeration Compressor

In mobile devices such as aircraft and electric vehicles, due to limited space, there are strict requirements on the volume and weight of the compressor mounted on the vehicle. Therefore, high-speed scroll compressors have attracted more and more attention because of their small size and light weight. In this paper, the numerical calculations and analysis of the three-dimensional (3D) transient flows in a high-speed scroll refrigeration compressor were established and validated. Circumferential gas intake was used in the simulation. According to the actual compressor size, the mesh generation accurately considers clearances. The radial and the axial clearances were both set as 0.01 mm. A dynamic and high-quality hexahedral structured mesh was generated for the working chamber, and the problem of insufficient grid density in radial clearance was solved. When the rotational speed was set as 3000 rpm, 6000 rpm, and 9000 rpm alternatively, the difference in the volume efficiency of the simulation and the experiment results was below 6.3%. The results show that the higher rotational speed contributed to the greater pressure fluctuation in the compression chamber and the discharge process, and the over-compression phenomenon was more obvious. The maximum leakage velocity was 160 m/s, and the tangential leakage velocity was higher than the radial leakage velocity. Meanwhile, radial leakage velocity will increase significantly in high-speed operation mode. With the increasing rotational speed, the position of the maximum axial and tangential leakage velocity was closer to the start of the scroll. Therefore, the seal of the scroll starting part is very important in the design of a high-speed scroll compressor.

Analysis of Tangential Leakage Flow Characteristics of Oil-Free Scroll Expander for a Micro-Scale Compressed Air Energy Storage System.

Tangential leakage loss is the primary factor that significantly affects the output performance of oil-free scroll expanders. A scroll expander can function under different operating conditions, and the flow of tangential leakage and generation mechanism is different. This study employed computational fluid dynamics to investigate the unsteady flow characteristics of the tangential leakage flow of a scroll expander with air as the working fluid. Consequently, the effects of different radial gap sizes, rotational speeds, inlet pressures, and temperatures on the tangential leakage were discussed. The tangential leakage decreased with increases in the scroll expander rotational speed, inlet pressure, and temperature, and decreased with decrease in radial clearance. With an equal-proportional increase in radial clearance, the flow form of the gas in the first expansion and back-pressure chambers became more complicated; when the radial clearance increased from 0.2 to 0.5 mm, the volumetric efficiency of the scroll expander decreased by approximately 5.0521%. Moreover, because of the large radial clearance, the tangential leakage flow maintained a subsonic flow. Further, the tangential leakage decreased with increase in rotational speed, and when the rotational speed increased from 2000 to 5000 r/min, the volumetric efficiency increased by approximately 8.7565%.

An Improved Geometric Theoretical Model and Throughflow Prediction Method for a CO2 Scroll Compressor of Automotive Air Conditioning System

The scroll-type compressor is the core component of the refrigeration system using the natural refrigerant carbon dioxide. An accurate scroll geometric theoretical model is essential for evaluating and enhancing compressor performance. The present paper proposed and validated an improved geometric theoretical model of a scroll compressor. A vector triangle method-based general piecewise function describes precisely the volume variation of the working chambers, based on which the transient throughflow modeling and performance evaluation of a carbon dioxide scroll compressor were conducted. The mechanisms and influencing factors of the suction precompression and the asymmetry discharging were analyzed. The results indicate that the strength of the suction precompression is mainly influenced by the suction vacuum under different rotating speeds, partly associated with the tangential leakage under low rotating speeds. The increasing initial suction pressure contributes to the linear raising of the pressure difference between suction initial and ending pressures, decreasing the precompression extension slightly. The variation of the discharge throughflow areas of two symmetric discharge chambers dominates the pressure asymmetry, which is gradually eliminated by the overlapping throughflow area. Compared with the circular discharge structure, the waist-shape port reduces the pressure asymmetry degree and shortens its duration.

A review of the research status of scroll expander

In order to solve the problem of energy crisis and take the road of sustainable development, the development of renewable energy and recycling of low-grade waste heat have attracted more and more attention. As a new type of volumetric energy conversion device, scroll expander is wi dely used in Organic Rankine Cycle (ORC) waste heat recovery, because of its advantages such as small size and so on. Scroll profile is one of the main factors affecting scroll expander performance. Compared with the traditional constant section scroll profile with same suction volume, volume ratio and shell size, the new type of variable section scroll profile could reduce scroll tooth height, better mechanical properties and improve efficiency, therefore making it more suitable for working under complex operating conditions. In order to reduce the head invasion rate, airflow friction factor, the power loss at the air inlet, and improve the pneumatic power conversion efficiency, a new head correction method is proposed. Although R123, R134 and R245 are the most commonly used working medium in scroll fluid machinery, the selection of working medium in scroll expander is still a key problem. The overall performance of the scroll expander can be improved by designing different inlet shapes and positions or double-symmetrical exhaust ports. The radial leakage caused by axial clearance of scroll expander can be improved by developing new scroll profile to reduce the length of radial leakage line and optimizing the design of scroll top sealing mechanism. The tangential leakage caused by radial clearance can be improved by enhancing the manufacturing precision and installation accuracy of scroll plate and designing the radial variable mechanism. At present, fewer research has been carried out on the leakage of scroll expander. Therefore reducing the leakage loss to improve the performance of scroll expander is of great significance in the future research.

Tangential leakage flow control with seal-grooves on the static scroll of a CO2 scroll compressor

• The seal-grooves are arranged on the sidewall of the static scroll. • Tangential leakage flow is reduced by the seal-grooves on the static scroll. • The seal-grooves arranged in the compression chamber brings more benefit. • Multi seal-grooves prolongs the energy dissipation of the tangential leakage flow. • Both streamwise and secondary axial vortex contribute to the sealing effect. Tangential leakage is an important factor affecting the aerothermodynamic performance of the scroll compressor, and existing methods to reduce tangential leakage usually aim at narrowing leakage path. In this paper, continuous seal-grooves arranged on the sidewall of static scroll was proposed, in order to achieve the passive flow control of the tangential leakage. Numerical methods were conducted to investigate the flow characteristics of tangential leakage in the radial clearance with seal-grooves. The impacts of diverse geometric parameters and arrangement schemes on the performance of the scroll compressor were also discussed. Results showed that throttling effect, flow separation of tangential leakage, and secondary axial turbulence was the main influence mechanism of the seal-grooves. Appropriate groove depth and spacing contributes to the developments of flow separation and secondary axial turbulence in seal-grooves, while increasing seal-groove number brought better flow control effect. Based on the above results, the seal-grooves arranged on the sidewall of compression chamber increased separately the volumetric efficiency and isentropic efficiency by 1.63% and 1.32%, and the volumetric efficiency also improved by 0.99% when the seal-grooves were arranged in the suction chamber. This work may provide a new flow control method of tangential leakage in the scroll compressor.

Unsteady characteristic and flow mechanism of a scroll compressor in small-scale compressed air energy storage system

Tangential leakage loss reduction has significant impact on improving the performance of scroll compressors. In this study, the flow field of a scroll compressor working with air was numerically investigated. The characteristics of the tangential leakage flow in different radial clearances were studied, which was obtained by analyzing the field quantities distributions. Moreover, the influence of radial clearance on the time-averaged performance of the scroll compressor and the aerodynamic force on it in each direction are analyzed. The results showed that the gas flowed into the low-pressure chamber through the radial clearance, and the downstream gas in compression chamber was compressed and collides with the leakage flow, having aggravated the uneven distribution of the flow field in the compression chamber. The gas velocity was faster in the region with large pressure difference, and the peak velocity appeared near the radial clearance. Moreover, as the radial clearance continues to increase in a certain range, its influence on the working characteristic curve of scroll compressor has two sides. The research can provide theoretical basis for the structural design of scroll compressors.

Design and characteristic analysis of dual-excitation and dual-modulation axial permanent magnetic gear

In order to solve the problems of serious axial and tangential leakage and low torque density in the magnetic circuit axial permanent magnet gear (APMG), an external regulating ring is introduced on the basis of APMG to form a dual-excitation and modulation APMG structure, namely DEM-APMG. The low speed rotor of DEM-APMG is clamped between the inner and outer magnetizing rings to generate dual-excitation field (i.e. dual excitation). At the same time, the inner and outer magnetizing rings modulate the low speed rotor dual-directionally modulation (i.e. dual modulation). The axial and tangential leakage flux of APMG can be converted into useful harmonics to increase the output torque and torque density on the basis of APMG. In this study, mathematical analysis is used to describe the air gap magnetic density and electromagnetic torque model of a DEM-APMG, which essentially describes the root cause of the increase in torque density. Using 3D finite element static and dynamic simulations, the transmission characteristics of the APMG and DEM-APMG are compared and analyzed. Results show that the maximum static torque of the DEM-APMG high-speed and low-speed rotors with the same outer diameter increase by 22.7% and 23.8%, respectively, compared with APMG, 26% and 29%, respectively, in steady-state operation, and the torque density increases by 24%. The influence of the primary structural parameters on the transmission characteristics is also investigated using the control variable method. Results show that the duty cycle of the magnet adjusting block, the axial length of the high-speed permanent magnet and the low-speed permanent magnet have the strongest effect on the torque density of the DEM-APMG. When the axial length of the high-speed permanent magnet and low-speed permanent magnet is 8mm, and the duty cycle is 0.4, the torque density can reach the optimal value of 156kNm/m3.

Flow characteristics of tangential leakage in a scroll compressor for automobile heat pump with CO2

Tangential leakage loss reduction has great significance on improving the performance of scroll compressors. In this study, the flow field of a scroll compressor working with CO2 was numerically investigated. The development characteristics of the tangential leakage flow in different working chambers were carried out, which was obtained by analyzing the field quantities distributions. The impacts of the radial clearances and sidewall roughness on the tangential leakage were also taken into consideration, in order to explore the feasible method of the flow control for the tangential leakage in scroll compressors. Results showed that the tangential leakage flow had various characteristics in the suction and compression chambers due to the different interactions between the tangential leakage flow and mainstream. Owing to little reverse pressure gradient, the tangential leakage flow maintained the typical jet form in the suction chambers. By contrast, the mixing of the tangential leakage flow and mainstream induced the passage vortex and secondary flows in the compression chamber. The secondary flow was the primary factor that results in the occurrence of localized high temperature region rather than the tangential leakage. With the increase of the radial clearance, the volumetric efficiency declined and the discharge temperature increased rapidly. In terms of flow control of the tangential leakage, the increase of sidewall roughness by 2 µm could achieve the same effect as the decrease of the radial clearance by 4 µm, while the volumetric efficiency increased by almost 5% and average discharge temperature decreased by 5 K.

Numerical analysis and correlations for radial and tangential leakage of gas in scroll compressors

Scroll compressors are positive displacement machines of orbital motion that compress a gas by means of two interfitting spiral-shaped scroll members. Gas leakage is an important source of inefficiency in scroll compressors and it therefore needs to be estimated. Currently, correlations for leakage required in simulation models are based on simplified flow conditions. Thus, a high degree of uncertainty is associated with leakage predictions for the wide range of operating conditions found in actual applications. This paper reports a numerical analysis of radial and tangential leakage in scroll compressors considering different gases, operating conditions and geometries expressed as dimensionless parameters. Numerical models were developed to analyze the aforementioned phenomena in detail, including the geometry of the wraps. Based on the predicted values, correlations for the radial and tangential leakage of gas particularly suitable for comprehensive simulation models were developed and validated through comparison with experimental data and other models available in the literature.

Numerical analysis of the transient leakage flow in axial clearance of a scroll refrigeration compressor

The transient flow model of a scroll refrigeration compressor which included axial clearance was established in the paper using PUMPLINX based on the computational fluid dynamics and the dynamic grid methodology. According to the actual size in the physical compressor, the flank and the axial clearances were set equal to 0.030 mm and 0.015 mm, respectively. As the fluid domain of the axial clearance was too small to generate enough layers of grids in PUMPLINX, it was first magnified 100 times to generate grids of high quality, and then the fluid domain and grids were recompressed to the original size. The simulation results were verified experimentally. The influence of the radial leakage on the downstream flow field was investigated. Moreover, the characteristics of radial and tangential leakage flows were analyzed. It was concluded that the predictions of the compressor performance, except the discharge temperature, are improved after the axial clearance was included in the model. The radial leakage is dominant while a portion of involute leakage flow exists near the flank clearance. The influence of radial leakage on the downstream temperature is lower than that of the tangential leakage in flank clearance. The tangential leakage flow is turbulent basically while the radial leakage flow is laminar. The tangential leakage is severer at the beginning of the discharge process, and the radial leakage is more remarkable at the end of the compression process. When the pressure ratio across the leakage path is higher than the critical pressure ratio, the tangential leakage flow becomes supersonic for the converging–diverging clearance structure, while the radial leakage flow remains subsonic due to the larger flow losses. The results obtained through this research could be applied to modify the current leakage models and optimize the clearances of scroll compressors.

Low-Loss Design and Analysis of Magnetic-Field Modulated Brushless Double-Rotor Machine

Due to the existence of large permanent magnet (PM) loss caused by its magnetic-field modulated (MFM) rotor in a traditional MFM brushless double-rotor machine (MFM-BDRM), a low-loss MFM-BDRM with the sinusoidal permeance characteristic of an MFM rotor is proposed and investigated in this paper. Since fan-shaped magnetic and nonmagnetic blocks in traditional MFM rotor cause many harmonic permeances and further produce large harmonic loss in the PMs, the ideal sinusoidal permeance model of an MFM rotor is first established and investigated by the analytical method. Considering that tangential leakage flux among magnetic blocks in the analytical method is difficult to calculate accurately, the influence of key parameters of the proposed MFM rotor, like the span ratio of magnetic block, minimum length of inner and outer air gap, on the electromagnetic performance of MFM-BDRM is further investigated and optimized by the finite-element method. Finally, to completely evaluate the performance of the proposed MFM-BDRM, a traditional MFM-BDRM with the same size is designed to compare performances under different operating conditions.

3D transient CFD modelling of a scroll-type hydrogen pump used in FCVs

The scroll pump has a great potential to recirculate hydrogen in a fuel-cell vehicle (FCV) because of its high efficiency, low noise and vibration, reliable operation, and a wide range of adjustable flow. This paper presents three-dimensional transient computational fluid dynamics (CFD) modelling of a scroll-type hydrogen pump used in FCVs, including leakage flow through both the radial clearance (RC) and axial clearance (AC). A dynamic mesh was generated for the moving orbiting scroll, and high-quality hexahedral structured grids with sufficient grid-density were applied to the clearances to solve the multi-scale problem. The pressure and velocity fields were obtained at different rotating angles to reveal the dynamic characteristics in the compression chambers. The simulation results showed that the radial leakage through AC has more significant influence on the volumetric efficiency than the tangential leakage through RC, especially on scroll-type hydrogen pumps. The presented modelling and simulation methods were validated experimentally by operating a scroll air compressor at different speeds and pressure ratios. The volumetric efficiency of the scroll pump was 85.39% with 0.02 mm AC and 0.02 mm RC, 81.43% with 0.02 mm AC and 0.04 mm RC, and 70.17% with 0.04 mm AC and 0.02 mm RC. Further, it was found that the performance of scroll-type hydrogen pumps is more sensitive to rotating speed than air scroll pumps under the same conditions. With hydrogen, the volumetric efficiency increased by 30.68% when the rotating speed was increased from 3000 r·min−1 to 6000 r·min−1; with air, the volumetric efficiency increased by 12.81%. Therefore, it is necessary to consider both AC and RC in the CFD modelling of scroll machines, particularly in the case of hydrogen scroll pumps.

Multiphysics Design of a V-Shape IPM Motor

In this paper, a multiphysics model is proposed for a multi-V-shape interior permanent magnet motor with concentrated winding. This paper develops a nonlinear magnetic model that computes the flux density in the motor. The analytical model includes several novel aspects: it takes into account the local saturation near the iron bridges, it proposes a method for modeling the concentrated tooth winding, and it calculates the slot tangential leakage flux and includes it in the flux linkage calculation. The magnetic model is coupled with an electrical model that computes the power factor and the voltage at the motor terminals. A loss model is developed in order to calculate the copper and the iron losses. They are used as inputs to a nodal thermal model that introduces a thermal circuit for concentrated end-winding and computes the temperature of the motor. A mechanical model is developed. It evaluates the mechanical constraints encountered by the structure. The models are verified using finite element computations and numerical calculations performed with dedicated software. Besides, the coupled analytical model is experimentally validated using a prototype motor. Finally, two multiphysics bi-objective optimizations are carried out in order to design the motor for high-torque and low-speed application.

Temperature field analysis of tangential clearance leakage flow for scroll compressor based on fuzzy ridgelet finite element method

ABSTRACTTo improve the computing precision and efficiency of temperature field analysis in tangential clearance of scroll compressor, the ridgelet finite element method is combined with fuzzy finite element method to construct the fuzzy ridgelet finite element method of analyzing temperature field in tangential clearance. First, the related research progresses on heat transfer of scroll compressor, wavelet finite element method, and fuzzy finite element method are summarized. Second, the leakage flow model of tangential clearance in scroll compressor is studied in depth. Third, the heat transfer model of leakage flow in tangential clearance of scroll compressor is established, and then the fuzzy ridgelet finite element model is constructed, the fuzzy finite element model is transformed to the random model based on information entropy, the corresponding calculating procedure is designed. Finally, the simulation analysis is performed based on fuzzy finite element method, fuzzy Daubechies wavelet finite element method, and the fuzzy ridgelet finite element model, respectively, comparing analysis between simulation and test results shows that the fuzzy ridgelet finite element method has best computing effectiveness on temperature field analysis of tangential clearance of scroll compressor. In addition, the tangential clearance temperature of scroll compressor with and without water cooling has been analyzed based on the fuzzy ridgelet finite element method, and the results show that the water cooling system can reduce the temperature in tangential clearance greatly.

Study on Mathematical Model in Working Process of Automotive Air Conditioning Scroll Compressor

In order to study the working features of automotive air conditioning scroll compressor, this paper uses mathematical model of working process to analyze it. After studying working process, a equation of suction volume is given. The thermodynamic model of compression chamber and back pressure chamber includes mass conservation and energy conservation. Based on Hydromechanics, leakage models of radial leakage and tangential leakage are discussed. The model lays a foundation of automotive air conditioning scroll compressor performance simulation.

Experimental Investigation of Turbine Leakage Flows on the Three-Dimensional Flow Field and Endwall Heat Transfer

Within a European research project, the tip endwall region of low pressure turbine guide vanes with leakage ejection was investigated at DLR in Göttingen. For this purpose a new cascade wind tunnel with three large profiles in the test section and a contoured endwall was designed and built, representing 50% height of a real low pressure turbine stator and simulating the casing flow field of shrouded vanes. The effect of tip leakage flow was simulated by blowing air through a small leakage gap in the endwall just upstream of the vane leading edges. Engine relevant turbulence intensities were adjusted by an active turbulence generator mounted in the test section inlet plane. The experiments were performed with tangential and perpendicular leakage ejection and varying leakage mass flow rates up to 2%. Aerodynamic and thermodynamic measurement techniques were employed. Pressure distribution measurements provided information about the endwall and vane surface pressure field and its variation with leakage flow. Additionally streamline patterns (local shear stress directions) on the walls were detected by oil flow visualization. Downstream traverses with five-hole pyramid type probes allow a survey of the secondary flow behavior in the cascade exit plane. The flow field in the near endwall area downstream of the leakage gap and around the vane leading edges was investigated using a 2D particle image velocimetry system. In order to determine endwall heat transfer distributions, the wall temperatures were measured by an infrared camera system, while heat fluxes at the surfaces were generated with electric operating heating foils. It turned out from the experiments that distinct changes in the secondary flow behavior and endwall heat transfer occur mainly when the leakage mass flow rate is increased from 1% to 2%. Leakage ejection perpendicular to the main flow direction amplifies the secondary flow, in particular the horseshoe vortex, whereas tangential leakage ejection causes a significant reduction of this vortex system. For high leakage mass flow rates the boundary layer flow at the endwall is strongly affected and seems to be highly turbulent, resulting in entirely different heat transfer distributions.

Leakage Flow Rate and Wall Shear Stress Distributions in a Biocentrifugal Ventricular Assist Device

In previous studies, the radial and tangential leakage flow velocities in the gap between the rotating impeller and the pump casing of a biocentrifugal ventricular assist device (VAD) model were obtained by hot wire. Based on the velocities obtained, the leakage flow rate through the clearance gap between the impeller and the stationary casing, as well as the wall shear stress distributions on the inner surface of the stationary casing, can be determined. By integrating the radial velocities numerically, the leakage flow rate through the clearance gap was found to be 6.43 x 10(-4) m3/s under operating conditions, which is 25.7% of the inlet flow. This is equivalent to approximately 1.7 L/min in the prototype. The leakage flow rate was found to be 5.22 x 10(-4) m3/s and 3.66 x 10(-4) m3/s under fully opened and fully closed conditions, respectively. The double volute design significantly affected wall shear stress distributions, with the high wall shear stress region concentrated at the beginning of the splitter plate under all three flow conditions. In contrast, the high wall shear stress region could only be observed at the cutwater in the fully closed condition. The highest wall shear stress was found to be 44.1 Pa, which is much lower than the threshold values that cause hemolysis. On the other hand, the lowest wall shear stress was found to be 21.31 Pa. This wall shear stress level is much higher than the shear stress required to disrupt aggregates of blood cells and platelets. These findings explain why hemolysis and thrombosis are at the low level in the clearance gap of this VAD.