Circumferential Flow Research Articles

Effects of Radial and Circumferential Flows on Power Density Improvements of Tubular Solid Oxide Fuel Cells

Improving the power density of SOFC stacks will accelerate their integration into mobile applications. We developed a 3D Multiphysics model validated by experimental results from early studies to examine the effect of radial and circumferential flows on the power density improvements in a micro-tubular SOFC. The inserts were placed inside the fuel channel to generate flow in different directions. The effects of geometric parameters of these inserts on flow and mass transfer in the fuel channel and porous anode were analyzed. We demonstrate that the radial flow enables the fuel to penetrate directly into the porous anode, increasing the local fuel concentration and enhancing the fuel diffusion to the anode triple-phase boundaries. We found that the circumferential flow has a negligible effect on the diffusion process in the anode and on the increase in power density. The impact of local convective and diffusive mass transfer mechanisms on power density improvement is analyzed using the local Péclet number along the axial direction. Enlarging the radial velocity component perpendicular to the porous anode could effectively increase the power density of the micro-tubular SOFC by 37%. This study helps improve our understanding of mass transfer in fuel channels and helps build a foundation for SOFC channel designs and optimizations.

On the rotordynamic performance of an annular gas seal with self-adaptive jet slots: Comparisons to the swirl brake and shunt injection

The positive circumferential flow is the main cause of seal instability in turbomachines. This paper proposed an annular gas seal with self-adaptive jet slots (SJS). The anti-swirl jet driven by the pressure difference between the seal domains is utilized to control the circumferential flow. The circumferential flow development and rotordynamic coefficients of the SJS are numerically calculated and compared with those of the labyrinth seal with typical anti-swirl methods (swirl brake and shunt injection). Results show that the SJS has the best anti-swirl effect on circumferential flow among the studied seals, thus showing the best stability. The leakage performance of the SJS is also improved due to the fluidic barrier induced by the anti-swirl jet.

Fluid-solid coupled simulation on thermal management of hydrodynamic gas foil bearing with an axial cooling throughflow

The axial throughflow cooling is a realistic solution for the purpose of thermal management in the hydrodynamic gas foil bearings operating at ultra-high rotational speed and mini bearing clearance. In order to illustrate the effects of axial throughflow cooling within the fluid-solid coupled heat transfer mode on the aerodynamic and thermal behaviors of hydrodynamic gas foil journal bearing, a steady three-dimensional fluid-solid coupled numerical simulation is performed in the present study by assuming that the journal-bearing works in a steady-state condition with a fixed eccentricity ratio of 0.9. The results show that the shearing-induced circumferential flow is significantly dominant in the hydrodynamic air film layer. At both edges of the foil bearing section, local suction flow into the bearing clearance and local leakage flow out the bearing clearance happen simultaneously at different circumferential positions. The increase of axial throughflow mass flowrate plays an effective role on improving the cooling capacity. However, it should be noteworthy that the bleeding air pressure is prompted in a nearly quadratic relationship along with the increase of axial throughflow mass flowrate. Due to the non-uniformity nature of viscous-shearing heat generation inside the hydrodynamic gas foil bearing with a big eccentricity, the temperature on the shaft and top foil surfaces takes on a non-uniform distribution. The peak temperature generally has a 20 K–30 K difference with respect to the mean temperature.

Design and modelling methodology for a new magnetorheological damper featuring a multi-stage circumferential flow mode

Design and modelling methodology for a new magnetorheological damper featuring a multi-stage circumferential flow mode

Rotor-stator aerodynamic interaction of centrifugal compressor at pulsating backpressure conditions

The performance of a centrifugal compressor is strongly influenced by pulsating backpressure condition, but little knowledge of the mechanism has been obtained. This study investigates aerodynamic interaction between impeller and volute at pulsating condition via experimentally validated numerical method. Results show that the features of volute-induce distortion at impeller exit are closely coupled with pulsating backpressure at different operational conditions. Specifically, the volute-induce pressure distortion varies out-of-phase with the mass flow rate near surge condition (OP2), but in phase near choke condition (OP1). The circumferential flow distortion at the impeller outlet manifests a notably unsteady effect at pulsating conditions for both OP1 and OP2. Comparing with the quasi-steady cases, the magnitude of the distortion is alleviated maximally by 2.3% and 2.7% for OP1 and OP2, respectively. The evolution of secondary flow patterns in the impeller show that an array of vortex tubes appears in the shroud region of the inducer downstream the main blade leading edge. It is resulted from the rolling-up of vortex sheet due to the K-H instability. The pulsating backpressure can profoundly depress the development of the vortex street. Therefore, the blockage effect by the vortex street in the inducer is alleviated.

Pulse Reverse Plating of Copper Micro-Structures in Magnetic Gradient Fields

Micro-structured copper layers are obtained from pulse-reverse electrodeposition on a planar gold electrode that is magnetically patterned by magnetized iron wires underneath. 3D numerical simulations of the electrodeposition based on an adapted reaction kinetics are able to nicely reproduce the micro-structure of the deposit layer, despite the height values still remain underestimated. It is shown that the structuring is enabled by the magnetic gradient force, which generates a local flow that supports deposition and hinders dissolution in the regions of high magnetic gradients. The Lorentz force originating from radial magnetic field components near the rim of the electrode causes a circumferential cell flow. The resulting secondary flow, however, is superseded by the local flow driven by the magnetic gradient force in the vicinity of the wires. Finally, the role of solutal buoyancy effects is discussed to better understand the limitations of structured growth in different modes of deposition and cell geometries.

Performance and near-wake characteristics of a bidirectional horizontal-axis tidal turbine

Horizontal-axis tidal turbines (HATTs) have the potential to produce considerable amount of clean renewable energy from ocean tides. To reduce costs and improve reliability, a full-scale bidirectional HATT (BHATT) with a centrosymmetric hydrofoil was designed to operate in two opposite flow directions. To better understand the performance and the near-wake characteristics of the BHATT, a three-dimensional (3D) numerical model with a k-ω SST model and a sliding mesh method was applied. The numerical framework was validated using two different experiments, and the mesh convergence was tested. The result shows that the BHATT can achieve a power coefficient of 43.5% at design tip speed ratio (TSR), and cause a remarkable circumferential flow in the near-wake from it. In addition, the presence of a support structure causes a decrease and a fluctuation in both power and thrust coefficient, especially when the rotor is downstream from the support structure. Similarly, a misalignment also leads to a decrease in both power and thrust coefficient. However, it causes almost no fluctuation. Finally, the influence of different support structures on the performance of the BHATT in different misalignment cases was studied.

Crystallization, microstructure and mechanical properties of directionally oriented films prepared using a novel blowing‐film process

AbstractA novel process of film preparation using a self‐made internal mandrel and external mold reverse rotation die is proposed. In this process, the mold's inner mandrel and outer parts rotate in opposite directions to achieve melt circumferential shear flow. In the blowing‐film process, a polymer melt is subjected to a flow field composed of extruded pressure extrusion and the reverse rotation of the die. The equipment has been used to successfully prepare low‐density polyethylene films. The microstructure and properties of films obtained under various internal and external reverse rotation speeds were studied. The results show that the rotation speeds are beneficial for forming a highly ordered crystalline structure of the film. As a result of microstructure evolution, the transverse direction (TD) tensile strength was enhanced by 39.4% and the machine direction (MD) tensile strength was enhanced by 47.4%. TD and MD breaking elongation increased by 38% and 43%, and the TD tensile breaking stress from 7.41 MPa was enhanced up to 10.79 MPa and the MD tensile breaking stress from 7.24 MPa was enhanced up to 11.26 MPa. The TD and MD tear strength increased by 38.2% and 28.3%. This novel blowing‐film process can be used to control the microstructure of films by controlling process parameters to improve the mechanical properties of films. © 2022 Society of Industrial Chemistry.

Numerical study of the effect of Inlet paired Swirl on Performance and Stability of Axial compressor

In order to study the effect of inlet paired swirl distortion on the performance and stability of compressor, a full-annulus unsteady numerical simulation of the effects of swirl distortion on performance and stability of transonic rotor Rotor 37 is carried out in this paper. The result shows that: the rotor performance deteriorates and the stable working range decreases under the effect of vortex flow distortion; the circumferential side flow caused by vortex swirl distortion leads to the uneven circumferential distribution of flow parameters at the inlet and the outlet of the compressor; the rotor blade has a very significant attenuation effect on the swirl distortion, and the swirl distortion intensity decreases along the axial direction; the circumferentially inhomogeneous distribution of rotor angle causes excessive local aerodynamic load on the rotor, and high intensity leakage vortices and excitation vortices are generated at the blade tip. The circumferentially unevenly distributed swirl angle causes excessive local aerodynamic load of the rotor, resulting in high-intensity leakage vortex and shock wave interference in the blade tip area, which severely blocks the flow path and eventually leads to unstable flow in the Rotor37.

Annular seal rotordynamic stability enhancement with circumferential spiral flow control using helical deflectors

Annular seal rotordynamic stability enhancement with circumferential spiral flow control using helical deflectors

Development and application of a numerical analysis method for investigating hydro static and hydrodynamic responses of pocket bearing rotor systems

A numerical tool is presented for simulating the dynamics of a vertical rotor attached with pocket bearing assembly immersed in a liquid pool. The journal of the bearing has a heterogeneous geometry with the presence of pockets and grooves. The fluid pressure supplied to the pockets is a quadratic function of shaft speed. The radial, circumferential and axial flow paths constitute a complex fluid network in the coupled system. The network has been conceived as an assemblage of straight and curved fluid flow paths for the generic applications. An efficient solution strategy has been employed involving both analytical and numerical techniques.A Case study was performed on a representative pocket bearing assembly that is commonly used in the coolant pumps of sodium cooled fast reactor. The study has brought out some specific dynamic characteristics of such bearings. The flow field exhibits both hydrostatic and hydrodynamic effects, thereby hybrid bearing characteristics. The dynamic characteristics are strong function of spinning velocity, eccentricity and angular orientation of the rotor in fluid annulus. Based on an elaborate parametric study, a rotor dynamic stability chart has been established for the practical applications. Interestingly, the dynamic behavior within a limited operating regime exhibits the characteristics of a large eccentric homogeneous rotor rotating in fluid annulus with moderate gaps, predicted by Antunes et al. (1996). Moreover, it is found that the pocket type bearing has better stability control, mainly due to lower added fluid mass. The numerical tool is experimentally validated by comparing the displacements measured on a shaft coupled with pocket bearing assembly, rotating in a water pool.

Experimental study on heat transfer characteristics of sub-cooled flow boiling in tube bundle channel under rolling motion

Rolling motion usually shows great influence on the dynamic and heat transfer characteristics in some marine nuclear power plants compared with land-based ones. The existence of two-phase fluid will aggravate the effect of rolling motion, indicating significant difference on the heat transfer mechanism. In present study, sub-cooled flow boiling in a vertically arranged tube bundle channels is experimentally investigated under various rolling motions. Results show that, when the rolling motion illustrates negligible effect on the mass flow rate, the influence of rolling motion can be attributed to the periodic change of the interface between hot and cold fluids as well as the circumferential transverse flow. A delay may occur on the fluid temperature since the rolling motion starts, while the delay of wall temperature variation is negligible. In addition, the farther away the flow channel is from the rolling axis, the more obvious the effect of the rolling motion is. Various rolling parameters including period and amplitude are considered. Note that the period of relevant parameters increases with after rising the rolling period, and the amplitude of fluid temperature increases with the increase of rolling frequency and amplitude. In comparison to the parameter of rolling amplitude, the rolling period displays a more critical role on the changes of wall temperature.

Analysis of the Formation Mechanism of Secondary Tip Leakage Vortex (S-TLV) in an Axial Flow Pump

Studies on the tip leakage vortex (TLV) are extensive, while studies on the secondary tip leakage vortex (S-TLV) are rare. To advance the understanding of the formation mechanism of the S-TLV, turbulent cavitating flows were numerically investigated using the shear stress transport (SST) turbulence model and the Zwart–Gerber–Belamri cavitation model. The morphology and physical quantity distribution of the S-TLV under two cavitation conditions were compared, and its formation mechanism was analyzed. The results reveal that in the lower cavitation number case, there is a low-velocity zone of circumferential flow near the tip in the back half of the blade. The shear vortices formed by the leakage jet gradually accumulate and concentrate in the low-velocity area, which is one of the main sources of the S-TLV. Meanwhile, the radial jet pushes the vortices on the suction surface to the tip, which mixes with the S-TLV. The flow path formed by the radial jet and the leakage jet is in accordance with the rotation direction of the S-TLV, which promotes the S-TLV’s further development. Under the conditions of a small cavitation number and low flow rate, the circumferential velocity and radial velocity of the fluid near the gap have altered significantly, which is conducive to the formation of the S-TLV.

Коэффициент скорости тангенциального подвода дозвуковой центростремительной турбины

Today, in the spectrum of tasks solved by orbital spacecraft, there is a direction associated with an increase in both functional and thermal power radiated by the thermal control system into outer space. At thermal power more than 7 kW, there is a shortage of heat-radiating surfaces. The problem can be solved in three directions: increasing the temperature of the radiating surface; unfolding additional surfaces; utilization of thermal energy in the organic Rankine cycle. The key link in the implementation of the cycle is the modeling and design of a low-potential jet microturbine. When modeling the working process of such a turbine, a preliminary assessment of energy losses during the formation of a circumferential flow at the impeller inlet is necessary. One of the parameters determining part of the losses is the velocity coefficient φu . This work is devoted to the theoretical substantiation and method of experimental determination of the coefficient in the range of geometric and regime parameters of the tangential supply of a subsonic centripetal turbine.

THE IMPACT OF SELECTED PARAMETERS ON PRESSURE DISTRIBUTION IN THE FACE THROTTLE OF A CENTRIFUGAL PUMP AUTOMATIC BALANCING DEVICE

Face throttles are a necessary functional element of non-contact face seals and automatic balancing devices of centrifugal pumps of different constructions. To calculate the hydrodynamic forces and moments acting on the rotor and fluid flow through the automatic balancing device, it is necessary to know the pressure distribution in the cylindrical and face throttle when considering all important factors which predetermine fluid flow. The face throttle surfaces are moving, which leads to unsteady fluid flow. The movement of the walls of the face throttle causes an additional circumferential and radial flow, which subsequently leads to the additional hydrodynamic pressure components. The paper analyses viscous incompressible fluid flow in the face throttle of an automatic balancing device taking into account the axial and angular displacements of throttle’s surfaces and the inertia component of the fluid. The effect of local hydraulic losses as well as random changes in the coefficients of local hydraulic resistance at the inlet and outlet of the throttle is analysed.

On the dynamic performance of a novel airfoil guider seal with the controlled circumferential flow: Numerical analysis and experimental validation

The positive circumferential flow is the major cause of seal instability. This paper proposes the airfoil guider seal (AGS) with specially designed airfoil guiders in cavities. The pressure difference between the suction and pressure surfaces induced by the airfoil guiders controls the circumferential flow. To validate the novel design, the flow field and flow-induced tangential force of the AGS are numerically calculated and compared with these of labyrinth seals (with/without swirl brakes), and pocket damper seal. The aerodynamic work and rotordynamic coefficients of the AGS are experimentally identified and compared with these of the labyrinth seal (with/without swirl brakes). With the airfoil guiders, the positive circumferential flow is effectively controlled. The AGS possesses the best stability among the studied seals.

Flow Pattern of Rotating Stall Cell in Axial Compressor

The results of measurements of the three-dimensional flowfield in a low-speed single-stage compressor operating in deep rotating stall are presented in this paper. The measurement technique includes a specially designed omnidirectional five-hole pressure probe, a specially designed near-wall hot-wire probe, high-frequency pressure transducers, and oil flow visualization. The test results provide a detailed description of the flow in and around the stall cell. The flow pattern of the cell is described by velocity vectors, streamlines, and pressure contours. A definition of the stall cell is proposed by using the streamlines in the frame of reference of the stall cell. Upstream of the rotor, the stall cell is characterized by a reversed jet flow at the rotor’s tip and downstream flow at the midspan and hub. Downstream of the stator, the stall cell is composed of low-speed wake flow with circumferential flow near the shroud from the trailing edge to the leading edge of the stall cell.

Characterization and Development of Universal Ventricular Assist Device: Computational Fluid Dynamics Analysis of Advanced Design.

We are developing a universal, advanced ventricular assist device (AVAD) with automatic pressure regulation suitable for both left and right ventricular support. The primary goal of this computational fluid dynamics (CFD) study was to analyze the biventricular performance of the AVAD across its wide range of operating conditions. An AVAD CFD model was created and validated using in vitro hydraulic performance measurements taken over conditions spanning both left ventricular assist device (LVAD) and right ventricular assist device (RVAD) operation. Static pressure taps, placed throughout the pump, were used to validate the CFD results. The CFD model was then used to assess the change in hydraulic performance with varying rotor axial positions and identify potential design improvements. The hydraulic performance was simulated and measured at rotor speeds from 2,300 to 3,600 revolutions/min and flow rates from 2.0 to 8.0 L/min. The CFD-predicted hydraulic pressure rise agreed well with the in vitro measured data, within 6.5% at 2300 rpm and within 3.5% for the higher rotor speeds. The CFD successfully predicted wall static pressures, matching experimental values within 7%. High degree of similarity and circumferential uniformity in the pump's flow fields were observed over the pump operation as an LVAD and an RVAD. A secondary impeller axial clearance reduction resulted in a 10% decrease in peak flow residence time and lower static pressures on the secondary impeller. These lower static pressures suggest a reduction in the upwards rotor forces from the secondary impeller and a desired increase in the pressure sensitivity of the pump. The CFD analyses supported the feasibility of the proposed AVAD's use as an LVAD or an RVAD, over a wide range of operating conditions. The CFD results demonstrated the operability of the pump in providing the desired circumferential flow similarity over the intended range of flow/speed conditions and the intended functionality of the AVAD's automated pressure regulation.

Performance of a Long Smooth Multiphase Pump Seal in Different Flow Regimes

Abstract Demanding for multiphase pumps introduces new challenges to the pump design. To prevent machine failures, the performance of the pump (noncontact) annular seal under multiphase conditions needs to be studied. The air addition into the oil flow not only changes the properties of the fluid but also can change the flow status in the seal clearance. The flow status can significantly affect the performance of the pump seal and thereby impact the pump vibration performance. Within the seal annulus, the axial direction flow is dominated by the pressure drop through the seal and can be considered as a Poiseuille flow. The circumferential direction flow is driven by the rotor rotation and can be considered as a Couette flow. The regime of the flow in the seal is controlled by the axial Reynolds number and the circumferential Reynolds number. Published test results on the boundaries between the laminar, transitional, and turbulent regimes in an annular seal are scant. This article will first draw these boundaries based on the test data for long smooth pump seals. Then, this article will show the performance of the long smooth pump seal in different flow regimes. Predictions will also be presented to compare with test results under different flow conditions.

Three-Dimensional Flow Simulation of a Twin-Screw Pump for the Analysis of Gap Flow Characteristics

AbstractUnsteady three-dimensional flow simulations on a twin-screw pump are performed for an assessment of the radial, circumferential, and flank gap flow effect on the pump performance. By means of the overset grid technique, rigid computational grids around the counter-rotating spindles yield a high cell quality and a high spatial resolution of the gap backflow down to the viscous sublayer in terms of y+<1. An optimization of the hole-cutting process is performed on a generic gap flow and transferred to the complex moving gaps in the pump. Grid independence is ensured, and conservation properties of the overset grid interpolation technique are assessed. Simulation results are validated against measured pump characteristics. Pump performance in terms of pressure build-up along the flow path through the spindles and volume flow rate is presented for a wide range of spindle speed and pump head. Flow rate fluctuations are found to depend on head but hardly on speed. By a profound assessment of the respective radial, circumferential, and flank gap contribution to the total backflow, the importance of the most complex flank gap is pointed out. Backflow rate characteristics in dependence on the pump head and the pump speed are presented.