Flow Passage Geometry Research Articles

Effect of ground tire rubber media's viscoelasticity and flow passage geometry on the abrasive flow finishing of helical gear

This work aims to elucidate the behavior of viscoelastic ground tire rubber media (GTRM) under abrupt contraction and expansion of the media at the entry and exit of the gear flow channel and its influence on polishing results. Due to the inherent nature of the abrasive flow finishing (AFF) process, the media flow converges at the entrance of the gear tooth as it flows from a larger fixture cross-section to a narrower volumetric space between gear teeth. The material removal and subsequent surface roughness rely heavily on the flow's pressure and velocity. A numerical simulation was performed to obtain the pressure and velocity along the gear flank face width (FFW). To investigate the effect of variation in the media deformation rate along the gear flow channel on AFF results, the material removal height and improvement in average surface roughness at different locations along the tooth flank face width were measured. AFF results reveal that the material removal near the two edges of the gear tooth is higher and has an inferior surface finish compared to the tooth's center. Due to the abrupt compression of the media at the flow channel entrance, the media act elastically dominant, resulting in high pressure and flow velocity near the tooth edge (flow channel's entry). Additionally, the effect of the helix angle on the AFF of various helical gear (HG) was investigated. Among the three HGs chosen, the 30° HG produces the lowest surface roughness under moderate pressure and high velocity. The microhardness and fretting wear analyses further confirm that the AFF polishing increases the microhardness and wear resistance of the gear tooth surface as a result of work hardening and minimizing surface defects.

Evaluation of correlations for mass flow rate of refrigerant through electronic expansion valve in air—water heat pump system using R32

To measure mass flow rate of R32 through EEVs under real operating conditions, a commercially available air-water heat pump (AWHP) system was operated in as wide a range as possible. Measurements showed that the effect of oil circulation on the refrigerant mass flow rate of the test system was negligible. To examine whether they were able to predict refrigerant mass flow rate of R32 in a real operating heat pump systems, previous empirical correlations available in the open literature were compared against these measured data. Previous empirical correlations, except for those of Park et al. (2007), showed poor agreement with the present experimental data, with mean absolute percentage error (MAPE) from 9.1% to 334.5% for EEV#1 (D: 2.40 mm) and from 24.1% to 122.2% for EEV#2 (D: 1.65 mm). These large differences were caused by differences in internal geometry of flow passage and operating conditions due to different refrigerants. A new empirical correlation was developed considering these aspects. The valve opening ratio was considered in terms of the valve flow coefficient variation. The thermodynamic state of refrigerant at the EEV inlet was represented by the enthalpy difference, so as to avoid discontinuity of the mathematical expression at the saturated liquid point. The new correlation showed good agreement with mass flow rate measured through both EEVs, with MAPE values of 9.3% and 14.5% for EEV#1 (D: 2.40 mm) and EEV#2 (D: 1.65 mm), respectively.

Development of refrigerant flow rate correlation for electronic expansion valve using valve flow coefficient

The mass flow rate of R32 through two different designs of electronic expansion valves (EEVs) was experimentally measured. A total of 173 mass flow rate data were produced with EEV1 (D1 = 2.40 mm) and EEV2 (D2 = 1.65 mm). Although there are numerous empirical correlations available for prediction of mass flow rate through an electronic expansion valve (EEV), previous empirical correlations failed to predict these data with reasonable margins of error. This is because those correlations only incorporated geometry parameters related to the EEV orifice and needle, even though entire geometry of flow passage inside EEV affects flow rate. An empirical correlation was developed based on the experimental data. The entire geometry of the flow passage inside the EEV was represented by a single parameter known as the valve flow coefficient. The new empirical correlation is in good agreement with the experimental data of EEV1 and EEV2, with average deviations of 5.84% and 5.87%, respectively, even though only valve flow coefficient was used to represent EEV geometry.

Thermal effect on cavitation characteristics of a hydraulic torque converter

The performance of torque converters, which use hydraulic oil as the working medium to transmit power, are severely affected by the operating temperature because various oil properties, such as viscosity, density and saturated pressure, vary drastically with temperature change. To study the thermal effect on the cavitation characteristics of viscous oil, we developed a full flow passage geometry and computational fluid dynamics (CFD) model with cavitation based on the finite volume method (FVM) to predict and analyze cavitation behavior and thermal effect in a torque converter. The results show that the critical cavitation number and critical cavitation temperature of the tested torque converter are 9.2 and 30 °C, respectively, and increasing the temperature reduces the cavitation number and induces the generation and intensification of cavitation. Besides, although higher temperature improves the transmission efficiency and capacity constant of the torque converter, it greatly magnifies the influence of cavitation on the hydrodynamic performance. In severe cases, it reduces the hydraulic performance by 9.3% and the flow velocity by 11.8% at 100 °C. Meanwhile, the cavitation flow field and the configuration of cavitation are also greatly affected by temperature. About 11.9% of the surface of the stator blade was covered by cavitation bubbles with the vapor volume fraction of 88.1% at 100 °C. Moreover, 30–60 °C is the optimum operating temperature range in terms of cavitations effect with no pronounced cavitation occurrence or that the cavitation degree is too weak to affect the performance in the mentioned temperature range.

The Effect of Rotating Speeds on the Cavitation Characteristics in Hydraulic Torque Converter

Hydraulic torque converter is a kind of high speed rotating machine using viscosity hydraulic oil as working medium, and its internal flow field is very complex. Thereby cavitation can occur easily in the working process, resulting in severe degradation of torque converter performance, noise, vibration and even failure. In order to reveal the effect of rotating speeds on the cavitation characteristics, a full flow passage geometry and a computational fluid dynamics (CFD) model with cavitation were developed to analyze the flow behavior in the torque converter. The results show that cavitation occurs when the speed difference between pump and turbine exceeds 1400 rpm for the basic model torque converter, which could be used as a useful indicator for the occurrence and degree of severity of flow cavitation. The increase of pump rotating speed or the decrease of speed ratio will intensify cavitation, which reduces the hydraulic transmission capacity and efficiency by over 20%, and seriously alters the shape, size, vapor volume fraction and region of cavitation bubbles. In extreme cases, more than 80% of the area on the suction side of the stator blade could be covered by cavitation bubbles. Moreover, the increase of pump rotating speed also changes the critical cavitation number and extends the cavitation range towards high speed ratio conditions not previously affected. These findings can provide guidance on how to choose the operating conditions of the hydraulic torque converter and how to improve its hydrodynamic performance and stability.

Investigation on the effect of the flow passage geometry of diesel injector nozzle on injection process parameters and engine performances

AbstractIn the paper, the method based on optimization of flow passage geometry of diesel injector nozzle to improve the quality of fuel injection and atomization process has been studied. Designs of injector nozzles have been developed to enhance the quality of these processes. These nozzles’ feature is the implementation of local hydraulic resistances—different grooves on the needle tip, which enhance the flow turbulence in the nozzle's flow passage. Computational fluid dynamics (CFD) simulations were performed to study the effect of the nozzle flow passage geometry on parameters of fuel flow, such as mass flow rate, velocity, turbulence, and cavitation. The influence of local hydraulic resistances on the needle tip over these parameters has been evaluated. The optimal geometry of the grooves has been chosen. Experimental studies of a four‐cylinder diesel engine D‐243 equipped with injectors with serial and modified nozzles have been carried out. The possibility of improving the fuel efficiency and emission performances by using the modified nozzles has been confirmed. At the maximum power condition, the use of the modified nozzles reduced the brake‐specific fuel consumption from 275.2 to 270.4 g/(kW∙h) (by 1.7%) and reduced exhaust smoke from 23.5% to 12.5% on the Hartridge scale (by 46.8%). However, at the same time, the emission of NOx increased from 1743 to 1923 ppm (by 10.3%). Moreover, there was a tendency to decrease the content of CO and unburned HC in the exhaust gases.

Evaluation and Validation of Viscous Oil Cavitation Model Used in Torque Converter

Hydraulic torque converter is widely used in transmission units as it is able to provide variable speed and torque ratio, isolate vibration, and absorb shock. The pursuit of a highly packed power unit requires a high capacity/speed torque converter, consequently resulting in a higher risk for cavitation and severe performance degradation, noise, vibration, and even failure. Existing cavitation models generally focus on water, and the empirical parameters are not suitable for the cavitation prediction of torque converter which utilizes high viscosity oil as its working medium. This paper focused on the influence of parameters on the performance and cavitation characteristics of torque converter. A full flow passage geometry and different computational fluid dynamics (CFD) models with cavitation were developed to predict torque converter fluid behavior by resolving Reynolds-averaged Navier–Stokes equations using finite volume method (FVM). The numerical results indicated that nuclei volume fraction, vaporization coefficient, mean nucleation site radius, and maximum density ratio have great influences on the cavitation behavior. These parameters altered the degree of cavitation and the pressure distribution on the surface of stator blades, and affected the stall performance such as stall capacity factor and torque ratio. The cavitation model was then modified to improve calculation accuracy. The test results showed that the prediction error under stall operating condition was decreased from 6.7% to 2%. This study provides insight on the influences of the empirical parameters on both internal cavitation behavior as well as overall hydrodynamic performance.

Designing multi-rotor tidal turbine fences

An embedded Reynolds-Averaged Navier-Stokes blade element actuator disk model is used to investigate the hydrodynamic design of tidal turbines and their performance in a closely spaced cross-stream fence. Turbines designed for confined flows are found to require a larger blade solidity ratio than current turbine design practices imply in order to maximise power. Generally, maximum power can be increased by operating turbines in more confined flows than they were designed for, although this also requires the turbines to operate at a higher rotational speed, which may increase the likelihood of cavitation inception. In-array turbine performance differs from that predicted from single turbine analyses, with cross-fence variation in power and thrust developing between the inboard and outboard turbines. As turbine thrust increases the cross-fence variation increases, as the interference effects between adjacent turbines strengthen as turbine thrust increases, but it is observed that cross-stream variation can be mitigated through strategies such as pitch-to-feather power control. It was found that overall fence performance was maximised by using turbines designed for moderately constrained (blocked) flows, with greater blockage than that based solely on fence geometry, but lower blockage than that based solely on the turbine and local flow passage geometry to balance the multi-scale flow phenomena around tidal fences.

The influence of flow passage geometry on the performances of a supercritical CO2 centrifugal compressor

In this paper, based on the thermodynamic design of the supercritical carbon dioxide (sCO2) centrifugal compressor, the design idea of the flow passage geometries and the method to improve the performance of the sCO2 centrifugal compressor are discussed. With the help of commercial software ANSYS CFX, the influence of the shape of the leading edge and trailing edge is studied, and the elliptical leading edge makes the pressure ratio 10.30% higher and the efficiency 3.95% higher than the square leading edge. By changing the forward-swept angle and backward-swept angle of the leading edge, the effects of aerodynamic swept shape in sCO2 centrifugal compressor are discussed. The effect of the gap between the impeller blade and diffuser blade is discussed, and the 10 mm gap makes the performance best. The pressure ratio is increased by 2.5% compared with the original design, while at the same time the efficiency is slightly improved. In summary, based on thermal design of the sCO2 centrifugal compressor, the effects of different flow geometries are analyzed in detail.

Coupled Multipoint Shape Optimization of Runner and Draft Tube of Hydraulic Turbines

This paper suggests a method of simultaneous multi-objective shape optimization of hydraulic turbine runner and draft tube (DT) with the objective to increase turbine efficiency in wide range of operating points (OPs). Runner and DT are the main sources of energy losses in hydraulic turbines. Coupling runner and DT in computational fluid dynamics (CFD) analysis enables correct statement of boundary conditions for efficiency evaluation, while simultaneous variation of these components allows more flexible adjustment of flow passage geometry. Detailed runner parameterization with 28 free geometrical parameters and DT parameterization with nine free parameters are given. Optimization problem is solved using multi-objective genetic algorithm (MOGA). For each variation of runner and DT shapes, flow field in wicket gate (WG), runner, and DT is simulated using steady-state Reynolds-Averaged Navier–Stokes (RANS) equations with k-e turbulence model. Energy-based boundary conditions are used for the calculations, allowing determination of efficiency of the whole turbine in correspondence with International Electrotechnical Commission (IEC) standard. Formulations of multiple OP efficiency objective functions and constraints are discussed in detail. To demonstrate the advantages of simultaneous runner and DT variation, two optimization problems are solved for a medium specific speed Francis turbine. Namely, single runner and coupled “runner–DT” optimizations are carried out. It is shown that optimized runner–DT geometry outperforms the result of single runner optimization by about 0.3% in terms of average efficiency, showing the potential of the developed approach to improve multiregime turbine characteristics in practical design optimization problems.

Hydrodynamic Design of Thrust Ring Pump for Large Hydro Turbine Generator Units

Abstract Thrust-ring-pump is a kind of extreme-low specific speed centrifugal pump with special structure as numerous restrictions from thrust bearing and operation conditions of hydro-generator units. Because the oil circulatory and cooling system with thrust-ring-pump has a lot of advantages in maintenance and compactness in structure, it has widely been used in large and medium-sized hydro-generator units. Since the diameter and the speed of the thrust ring is limited by the generator set, the matching relationship between the flow passage inside the thrust ring (equivalent to impeller) and oil bath (equivalent to volute) has great influence on hydrodynamic performance of thrust-ring-pump. On another hand, the head and flow rate are varying with the operation conditions of hydro-generator units and the oil circulatory and cooling system. As so far, the empirical calculation method is employed during the actual engineering design, in order to guarantee the operating performance of the oil circulatory and cooling system with thrust-ring-pump at different conditions, a collaborative hydrodynamic design and optimization is purposed in this paper. Firstly, the head and flow rate at different conditions are decided by 1D flow numerical simulation of the oil circulatory and cooling system. Secondly, the flow passages of thrust-ring-pump are empirically designed under the restrictions of diameter and the speed of the thrust ring according to the head and flow rate from the simulation. Thirdly, the flow passage geometry matching optimization between thrust ring and oil bath is implemented by means of 3D flow simulation and performance prediction. Then, the pumps and the oil circulatory and cooling system are collaborative hydrodynamic optimized with predicted head-flow rate curve and the efficiency-flow rate curve of thrust-ring-pump. The presented methodology has been adopted by DFEM in design process of thrust-ring-pump and it shown can effectively improve the performance of whole system.

Hydrodynamic optimization of trust ring pump and lubricating oil system for large hydroelectric units thrust bearing

Thrust-ring-pump is a kind of extreme-low specific speed centrifugal pump with special structure as numerous restrictions form thrust bearing and operation conditions of hydro turbine generator unit. Because the oil circulating and cooling system with thrust-ring- pump has a lot of advantages in maintenance and compactness in structure, it has widely been used in large and medium-sized hydro-generator units. Since the diameter and the speed of the thrust ring is limited by the generator set, the matching relationship between the flow passage inside the thrust ring (equivalent to impeller) and oil bath (equivalent to volute) has great influence on hydrodynamic performance of thrust-ring-pump, additionally, the head and discharge are varying with the operation conditions of hydro-generator unit and characteristic of the oil circulating and cooling system. As so far, the empirical calculation method is employed during the actual engineering design, in order to guarantee the operating performance of the oil circulating and cooling system with thrust-ring-pump at different conditions, a collaborative hydrodynamic design and optimization of both the oil circulating and cooling system and thrust-ring-pump is purposed in this paper. Firstly, the head and discharge required at different conditions are decided by 1D flow numerical simulation of the oil circulating and cooling system. Secondly, the flow passages of thrust-ring-pump are empirically designed under the restrictions of diameter and the speed of the thrust ring according to the head and discharge from the simulation. Thirdly, the flow passage geometry matching optimization between holes inside the thrust ring and oil bath is implemented by means of 3D flow simulation and performance prediction. Then, the pumps and the oil circulating and cooling system are collaborative hydrodynamic optimized with predicted head- discharge curve and the efficiency-discharge curve of thrust-ring-pump. The presented methodology has been adopted by DFEM in design process of thrust-ring-pump and it shown that can effectively improve and guarantee the performance of the oil circulating and cooling system.

Numerical Study on Convective Heat Transfer of AL2O3/Water, CuO/Water and Cu/Water Nanofluids through Square Cross-Section Duct in Laminar Flow

In this paper the convective heat transfer of Al2O3/water, CuO/water and Cu/water nanofluids through a square cross-section duct in laminar flow with constant temperature boundary conditions is numerically investigated. Because of the size and volume constraints, it may be required to use square flow-passage geometries. A square cross section duct has the advantage of lower pressure drop, but it has a lower heat exchange rate than that of a circular duct. However, this study shows that this could be compensated by using nanofluids in these systems. A dispersion model was used to include the presence of nanoparticles. Results show that the Nusselt number was enhanced by increasing the concentration and decreasing the size of nanoparticles. Up to 77%, 68% and 59% enhancement in Nusselt number for Cu/water, CuO/water and Al2O3/water nanofluids at 4.0% vol of 10nm nanoparticles was achieved respectively.

Prediction of transient lubricating oil flows within the connecting-rod of a diesel engine

This paper develops Aa computer program for the unsteady flow analysis of diesel engine lubrication systems. The possibility of cavitations developing in the big-end bearing groove due to the reciprocating motion of the connecting rod is investigated at the designed running speeds. The flow passage geometry especially the head loss coefficients of the bearing grooves s affects the minimum values of the head and the point when the development of the cavitations is initiated As the loss coefficient at the big-end increases and that of the small-end decreases, then the cavitations can be initiated. An orifice can be used to suppress the development of the cavitations and the diameter ratio and the location needs to be carefully selected to avoid unnecessary pressure loss. The channel size in the connecting rod is also an important parameter for optimization of the overall lubrication system; as the pipe diameter decreases, the minimum head increases and suppresses the cavitations from developing The minimum head always appears at the trailing groove of the big-end bearing.

The Effects of Diesel Injector Needle Motion on Spray Structure

The internal structure of diesel fuel injectors is known to have a significant impact on the steady-state fuel distribution within the spray. However, little experimental or computational work has been performed on the dynamics of fuel injectors. Recent studies have shown that it is possible to measure the three-dimensional geometry of the injector nozzle, and to track changes in that geometry as the needle opens and closes in real time. This has enabled the dynamics of the injector to be compared with the dynamics of the spray, and allows computational fluid dynamics (CFD) simulations to use realistic time-dependent flow passage geometries. In this study, X-ray phase-enhanced imaging has been used to perform time-resolved imaging of the needle seat area in several common-rail diesel injection nozzles. The fuel distributions of the sprays emitted by these injectors were also studied with fast X-ray radiography. Correlations between eccentric motions of the injector needle valve and oscillations in the fuel density as it emerges from the nozzle are examined. CFD modeling is used to interpret the effect of needle motion on fuel flow.

Modelling the characteristics of axial compressor of variable flow passage geometry, working in the gas turbine engine system

Modelling the characteristics of axial compressor of variable flow passage geometry, working in the gas turbine engine system This paper concerns application of mathematical modelling methods to analyzing gas-dynamic processes in marine gas turbines. Influence of geometry changes in axial compressor flow passage on kinematical air flow characteristics, are presented. The elaborated mathematical model will make it possible to realize - in the future - simulative investigations of gas-dynamic processes taking place in a compressor fitted with controllable guide vanes.

Liquid-side fouling of heat exchangers. An integrated R & D approach for conventional and novel designs

Particulate fouling of heat exchangers is a major fouling category with very significant technical and economic implications. It is studied here as part of a study aimed at improving design standards for novel and conventional heat exchangers. New fouling data are reported for plate heat exchangers (of two angles of corrugation, 30 and 60°) and particles of mean size ∼5 μm. The flow passage geometry and the fluid velocity have a strong effect on the fouling resistance R f. These results show that fouling (under the test conditions) is adhesion controlled and that the maximum measured resistance R f is almost an order of magnitude smaller than the TEMA recommendations. Particle adhesion and removal from flat surfaces leads to improved understanding of particulate fouling mechanisms and facilitates interpretation of the above data. Tangential hydrodynamic forces appear to be responsible for particle detachment. For a specific particle size, a distribution of adhesive strengths is obtained (and not a single value), which is strongly influenced by pH and may be time-dependent for very small sizes. Various applications of the new results are outlined, including the interpretation of the measured adhesive force distributions in terms of the well-known particle sticking probability.

糸を用いた交差管内の流れの可視化

The flow in the intersecting region of two streams inside an X-shaped flow network is complex due to combined consequence of the ramming phenomena and the centri fugal force induced by the flow passage geometry. The flow visualization study was conducted using a recirculating flow loop with an intersecting duct installed between two head tanks of different heads. In this study, both the symmetric and asymmetric flows are investigated by the string method to visualize flow oscillations of the shear layer in the intersecting region. The difference in flow branching from the intersecting region due to a change in the intersecting angle is disclosed. The variation of oscillation amplitudes is found to be small in 60°and 90°intersecting ducts. It is also found that the center position of oscillation amplitudes is at one side and the dispersion of flow oscillation is small in case of the asymmetric level at upper tanks.

110 交差管内の流況

The flow in the intersecting region of two streams inside a X-shaped flow network is complex due to combined results of the ramming phenomena and the centrifugal force induced by the flow passage geometry. In order to determine the flow mechanisms, this study applies the particle tracing method to observe streamlines and the string method to visualize flow oscillations downstream from the intersecting region. Both the symmetrical and asymmetrical flows between the two branches are investigated.The intersecting angle and flow rates are varied to determine their effects on flow behavior. Flow oscillations in the downstream branches are found to be related to vortex formation.

The Comprehensive Design of Pumps, Water Turbines and Compressors

Centrifugal pumps and compressors perform the same function of fluid transference; a boiler feed pump also operating as a turbo-compressor, when deprived of water, illustrates the design problems involved in each sphere of duty. Water turbines are reversed pumps. Pump design theory has in the past been unnecessarily complicated; in contrast, a simple system taking into account the combination of impeller and casing gives satisfactory results over the whole range of size, specific speed and characteristics. Flow passage geometry, with exact knowledge of the accelerations in three dimensions, is attained by the concept of the impeller with its flow surfaces generated as a gear wheel, improving efficiency and cavitation performance. Critical speeds and mechanical failure modes illustrate the relationship of pumps to turbo-compressors. Experience of 20000 pumps and 700 water turbines from 5 gallons to 5 million gal/min (of which a statistically significant number were tested on site by the user's staff and instruments on a ‘no tolerance penalty/bonus’ contract) resulted in efficiency bonus payments ranging up to 10 per cent of the contract price. Worldwide, for comparable numbers, higher efficiencies have not yet been published. Imperial units are occasionally used to help mental arithmetic and to illustrate historical data.