S054013 回転楕円柱周りのはく離現象に関する研究([S05401]噴流,後流,およびはく離流れの基礎と応用:最前線(1))

Dynamics of a powered disk in clay soil

Rotating electrodes can effectively improve the processing performance of micro-electrical discharge machining (micro-EDM), but there is still a lack of systematic research on the specific effects of electrode rotation and rotational speed changes. In this paper, the effects of electrode rotation and rotational speed on the discharge channel, debris stress, and debris motion in micro-EDM were analyzed theoretically. An AISI304 sheet was used as the workpiece and helical tungsten carbide alloy as the electrode. The through-hole drilling experiments of micro-EDM were carried out at low and high discharge energy and different electrode rotational speeds. In terms of processing efficiency, the effects of electrode rotation and rotational speed on material removal rate (MRR), relative tool wear ratio (RTWR), and short circuit number were analyzed. The results show that MRR increases first and then decreases, RTWR and short circuit number decrease first and then increase. In the aspect of processing precision, the impacts of electrode rotation and rotational speed on taper angle and overcut were analyzed. The results show that the electrode rotational speed has little effect on the change of the taper angle. In addition, when the electrode rotational speed is small, there is no obvious change in overcut. When the speed is too high, the overcut increases obviously and shows a trend of continuous increase. Finally, by comparing the experimental results, the optimal electrode rotational speeds of micro-EDM with two kinds of discharge energy were determined. The final experimental results also verify the correctness of the previous theoretical analysis.

Summary Previous studies of citric acid/calcite have been limited to coreflood tests and bench-scale experiments. However, the kinetics of a citric acid reaction with calcite has not been measured. This paper gives, for the first time, the kinetics of citric-acid/calcite reaction, which will provide a better way to model the performance of citric acid as a standalone stimulation fluid. In this paper, the rotating disk apparatus was used to study citric-acid/calcite reaction at a pressure of 1,000 psi, temperatures from 25 to 50°C, citric acid concentrations from 1 to 7.5 wt%, and disk rotational speeds from 100 to 1,000 rev/min. The reaction rate of citric acid with calcite was found to be dependent on the initial citric acid concentration, disk rotational speed, and temperature. For example, at 50°C, the reaction was reaction-rate-limited at rotational speeds greater than 500 rev/min, using high initial citric acid concentrations (3, 5, and 7.5 wt%), while at low acid concentrations (1 and 2 wt%), the reaction was mass-transfer-limited even at high rotational speeds (1,000 rev/min). During the reaction of citric acid with calcite, calcium citrate precipitation occurred at different acid concentrations and rotational speeds. The amount of this precipitation was found to be a function of both the initial citric acid concentration and disk rotational speed. More calcium citrate precipitated at high initial citric acid concentrations, especially at high rotational speeds. Calcium citrate precipitation occurred at the calcite surface, even at low initial citric acid concentrations. Because of this precipitation, the equilibrium of the citric-acid/calcite reaction was disturbed and the reaction shifted toward the forward reaction (toward the products). Therefore, the overall reaction rate was governed mainly by the rate of the forward reaction, and, hence, it was modeled by a new simplified reaction-rate equation; rate = kf{Ka1·CB}n/2 The average value of the reaction order (n) was found to be 0.833. In addition, the value of the reaction-rate constant (kf)was determined at various temperatures. The effect of temperature on the reaction-rate constant was found to follow the Arrhenius law, where the activation energy was found to be 63.1 kJ/mol.

In this study, microstructural changes and mechanical properties during friction stir welding of AA7075-T6 have been investigated. Friction stir welding at relatively high rotational speeds ranging from 1000 to 1400 rpm and longitudinal speeds in the range of 40 to 80 mm/min have been performed and then microstructures and mechanical properties of the weldments have been studied. The results show that the rotational and longitudinal speeds have a significant effect on the microstructures as well as the mechanical behavior of the welded material while a fine grain structure is produced at higher ratio of rotational speed to longitudinal speed. On the other hand, for a given longitudinal speed, it is revealed that there is an optimum rotational speed which gives the highest tensile strength and elongation for the stirred zone.

The purification of BSA from yeast/BSA binary suspension using batchwise centrifugal filtration under various conditions is studied. Effects of suspension pH and rotational speed on the cake properties, filtration rate and protein recovery are discussed. The experimental results indicate that the filtration rate is significantly affected by the cake growth at the initial periods of filtration, and no evident rate difference can be found among different suspension pH values under a low rotational speed. However, the effect of cake compression becomes more dominant as rotational speed increases. The compression of yeast cake is irreversible and strongly affected by the suspension pH especially under a high rotational speed. The cakes formed at pH 3.0 possess the highest compressibility due to the yeast coagulation, while the average specific resistance of cake is the lowest at pH 7.0 because of the high zeta potential of yeast cells. In addition, the recovery of BSA can be as high as 95–98% under the operating conditions of this study. Since the BSA concentration in the filtrate keeps constant during the filtration under various rotational speeds, the recovery of BSA is dependent solely on the filtration rate in spite of the little adsorbed amount on the yeast cells. To operate under higher rotational speed and pH 7.0 is optimal from the viewpoint of economic operation time and protein recovery.

Steady simulations were performed to investigate tip leakage flow and heat transfer characteristics on the rotor blade tip and casing in a single-stage gas turbine engine. A typical high-pressure gas turbine stage was modeled with a pressure ratio of 3.2. The predicted isentropic Mach number and adiabatic wall temperature on the casing showed good agreement with available experimental data under similar operating condition. The present numerical study focuses extensively on the effects of tip clearance heights and rotor rotational speeds on the blade tip and casing heat transfer characteristics. It was observed that the tip leakage flow structure is highly dependent on the height of the tip gap and the speed of the rotor. In all cases, the tip leakage flow was seen to separate and recirculate just around the corner of the pressure side of the blade tip. This region of re-circulating flow enlarges with increasing clearance heights. The separated leakage flow reattaches afterwards on the tip surface. Leakage flow reattachment was shown to enhance surface heat transfer at the tip. The interaction between tip leakage flow and secondary flows that is induced by the relative casing motion is found to significantly influence the blade tip and casing heat transfer distribution. A region of critical heat transfer exists on the casing near the blade tip leading edge and along the pressure-side edge for all the clearance heights that were investigated. At high rotation speed, the region of critical heat transfer tends to move towards the trailing edge due to the change in inflow angle.

Friction stir welding (FSW) was used to join 3003-H18 non-heat-treatable aluminum alloy plates by adding copper powder. The copper powder was first added to the gap (0.1 and 0.2 mm) between two plates and then the FSW was performed. The specimens were joined at various rotational speeds of 800, 1000, and 1200 rpm at traveling speeds of 70 and 100 mm/min. The effects of rotational speed, second pass of FSW, and direction of second pass also were studied on copper particle distribution and formation of Al-Cu intermetallic compounds in the stir zone. The second pass of FSW was carried out in two ways; in line with the first pass direction (2F) and in the reverse direction of the first pass (FB). The microstructure, mechanical properties, and formation of intermetallic compounds type were investigated. In high copper powder compaction into the gap, large clusters were formed in the stir zone, while fine clusters and sound copper particles distribution were obtained in low powder compaction. The copper particle distribution and amount of Al-Cu intermetallic compounds were increased in the stir zone with increasing the rotational speed and applying the second pass. Al2Cu and AlCu intermetallic phases were formed in the stir zone and consequently the hardness was significantly increased. The copper particles and in situ intermetallic compounds were symmetrically distributed in both advancing and retreating sides of weld zone after FB passes. Thus, the wider area was reinforced by the intermetallic compounds. Also, the tensile test specimens tend to fracture from the coarse copper aggregation at the low rotational speeds. At high rotational speeds, the fracture locations are placed in HAZ and TMAZ.

Stationary shoulder friction stir welding has been used to weld 4-mm-thick 2219-T6 aluminium alloy at high rotation speeds. Strain plastic damage was applied to demonstrate the formation mechanism of welding defects at high rotation speeds above 2000 rpm. A three-way converging zone in the joint, in which materials of different microstructure characteristics converged from three directions during high tool rotation speed welding, was found. At the relatively high tool rotation speed, the significant differences in the microstructures would result in weld defects in this zone. It could be attributed to material toughness damage at high strain rate. With increasing tool rotation speed, the tensile strength of the joint constantly decreased. When the tool rotation speed varied from 2000 to 2600 rpm, the tensile strength decreased from 305 MPa (68.2% of the BM) to 238 MPa (53.2% of the BM).

The operational rotational speeds of hydroturbines change arbitrarily within a small range, and the friction power consumption caused by the asymmetric curl represents a technical difficulty in magnetofluid sealing. In this study, the pressure-withstanding value and equations for the asymmetric curl of a magnetofluid sealing device under different rotational speeds were deduced. By considering the magnetofluid sealing device characteristics with Halbach magnetic arrays, temperature fields under a static field and low rotational speed were calculated for determining the Halbach magnetofluid sealing device with the best sealing performance. Comparisons and analyses were performed with the friction power consumption and sealing pressure-withstanding value of the selected structure under high (3000 r/min), medium (1500 r/min), and low (300 r/min) rotational speeds and alternating work conditions of ±3, ±6, and ±9. The results indicated that changes in magnetic moment caused by changes in the external magnetic field are the primary cause of friction power consumption. Heat generation occurs concurrently with the friction power consumption. Consequently, the pressure-withstanding value of the magnetofluid sealing is reduced; the friction power consumption of the magnetofluid is directly proportional to the magnetic field strength, rotational speed, and alternating amplitude. Unstable states and asymmetry of the external magnetic field lead to nonlinear increments in the friction power consumption of the magnetofluid. A stable and symmetrical magnetic effect, with a smaller rotational speed and alternating amplitude leads to lower friction power consumption, resulting in a more ideal sealing effect.

In this paper the performance of an innovative, high speed, external gear pump have been measured and verified in order to evaluate its potential application as a reliable and efficient power unit for automotive, electro-hydraulic actuated, robotized transmissions. More in detail, this particular type of volumetric machine is built with two suction and two delivery ports and is specifically designed for extremely challenging operating conditions, mainly in terms of both rotational speed and delivery pressure. First of all, the most important hydraulic and mechanical performance parameters have been measured and analyzed, over a wide range of rotational speeds, spanning between 400 and 7000 rpm, and for two different operating temperatures, respectively equal to 40 and 60 °C. In this case, with the aim to increase the consistency of the experimental measurements, two external gear pumps, with exactly the same design geometry and features, have been tested and compared, also with available data coming from the pump manufacturer. All the experimental measurements have been performed with the help of a test bench, equipped with a double Cardan joint and an overdrive, specifically tailored for running the pump at high rotational speed and applying a delivery pressure of about 45 bar, very near to a typical actuation value of a high-performance automotive robotized transmission. At the end of this experimental work, it is possible to conclude that the high speed external gear pump here tested and analyzed can be considered a reliable and effective alternative hydraulic power unit for high-performance, automotive, robotized transmissions.

The labyrinth seal is effective in reducing leakage losses at the rotor blade top in the turbine. This study investigates the variation in labyrinth seal performance at different rotational speeds, different Reynolds numbers, and different tooth front angles. Three Reynolds numbers (Re = 6000, 10,000, 15,000), five rotational speeds (Ta/Re = 0, 0.01, 0.04, 0.08, and 0.1), and three tooth front angles(75 deg, 90 deg, and 102.4 deg) have been introduced. The variation of leakage losses and heat transfer under different conditions is compared and a detailed analysis of the flow field and energy losses is performed. The discharge coefficient is increased slightly with increased rotational speed for the same Reynolds number. This is caused by the high rotational speed reducing the throttling loss and vortex loss. The high rotational speed enhances the heat transfer at the tip wall of the passage, and also weakens the heat transfer at the tooth cavity bottom. Additionally, the sealing capacity of the labyrinth is better at large tooth front angles, which is caused by the reduction of frictional losses on the stator and eddy current losses in the tooth cavity. The change in local pressure loss also affects the velocity distribution along the channel, which is the reason for the change in the local Nusselt number.

Microstructural degradation control and dissimilar joint optimization through friction stir processing

The enhancement in the rate of the heat transfer resulting from rotating smooth and rough vertical cylinders, of 1.28 and 21.75μm average roughness, respectively, are experimentally studied. Experiments were carried out for cooling fluid Reynolds numbers from 3300 to 7800 with varying the rotational speed up to 280rpm. Experimental runs at the stationary case showed an acceptable agreement with the theoretical values. The experimental Nusselt number values at various rotational speeds are correlated as functions of Reynolds, Weber, and Prandtl numbers for smooth and rough surfaces. The correlated equations were compared with the correlation obtained by another author. The results show that the enhancement of the heat transfer rate becomes more appreciable for low Reynolds numbers at high rotational speeds and for high Reynolds numbers at low rotational speeds. The rotation causes an enhancement in the overall heat transfer coefficient of ∼89% at Re=7800, We=1084, and Pr=1.48 for smooth surface and of ∼13.7% at Re=4700, We=4891, and Pr=1.696 for rough surface. Also, the enhancement in the heat transfer rates utilizing rotary surface becomes more pronounced for the smooth surface compared with the rough one, therefore the choice of the heat transfer surface is very important. The present work shows a reduction in the heat transfer rate below its peak value depending on the type of the heat transfer surface. It is shown that the enhancement in the heat transfer, i.e., enhancement in the Nusselt number, depends on the Weber number value and the surface type while the Nusselt number value mainly depends on the Reynolds and Prandtl numbers. Correlated equation have been developed to represent the Nusselt number values as functions of the Weber and Reynolds numbers within the stated ranges of the parameters.

The thermoelastohydrodynamic performance of an inclined-ellipse dimpled gas face seal is analyzed. The pressure distributions of the gas film and temperature fields of the seal rings and gas film are presented considering thermal and elastic distortions. Then, the influences of texturing parameters, including dimple inclination angle and dimple depth, on sealing performance are investigated under different operating parameters such as rotational speeds and seal pressures. The results show that face distortions lead to a decrease in the hydrodynamic effect at high rotational speed. The analysis shows that the opening force can decrease by more than 50% as the rotational speed increases from 0 to 35000 r min−1. The influence of face distortion on the seal performance, such as opening force and leakage characteristic, gradually increases with the rotational speed.

This paper presents a study on friction stir processed 1100 aluminum withincorporation of rice huskash derived, amorphous silica particles and fabricated at different tool rotational speeds. During friction stirring amorphous silica powder was placed into a groove made in the joining line of Al 1100 plates. Friction stirringwas performed with clockwise tool rotational speeds of 600 rpm, 865 rpm, 1140 rpm or 1500 rpm with a constant 45 mm/min travelling speed and a 2° tilt angle. High rotational speed (1140 rpm) facilitated material flow in the stir zone, contributing to fine aluminum matrix grain size (30- 10μm) as a result of dynamic recrystallization. Stirring at this rotational speed also caused the fracturingrelated refinement of silica particles to 10μm particle sizethat isassociated with good distribution in the aluminum matrix. Reduction in wear rate of friction stir processed Al1100 with improved hardness was believed to be due to the presence of hard silicawith high interfacial strength and high hardness of recrystallized aluminum grains in the stir zone.