High Circumferential Speeds Research Articles

Highly efficient centrifugal compressors series development for the turbo-cooling machines

BACKGROUND: Currently, there is a growing demand for single-stage centrifugal compressors with a high pressure ratio. Such requirements encourage the use of high-pressure stages with high circumferential speeds u2 300 m/s, which leads to increased levels of Mach number and, as a consequence, pressure losses. Work to improve the efficiency of such steps leads to a reduction in energy consumption and an increase in the cooling capacity of refrigerating machines.
 AIMS: To develop a series of ten highly efficient high-head model centrifugal compressors with the pressure ratio of c = 2.0.
 MATERIALS AND METHODS: a complex calculation technique developed by the authors is used to increase the efficiency of the stages of centrifugal compressors. The method consists of sequential execution of 4 stages: gas dynamic calculation, profiling, three-dimensional viscous calculation, multiparametric optimization.
 RESULTS: a series of the model centrifugal compressors has been designed for the following range of design mode parameters: conditional flow coefficient 0.035 Fr0.12; theoretical head coefficient t.p. =0.74; conditional Mach number 0.93Mu0.96. The estimated isentropic efficiency of the developed centrifugal compressors ranges from 77% to 84%, depending on the flow rate of the stage.
 CONCLUSIONS: a series of ten highly efficient flow parts of centrifugal compressors have been developed, which can be used in gas-dynamic projects when designing modern centrifugal compressors.

Estimating the optimal value of diameter of the inlet to the impeller of a centrifugal blood pump

The article is devoted to the optimization of the design of the inlet zone of a centrifugal blood pump. One of the disadvantages of such pumps is the generation of turbulence in the flow of the pumped fluid, which contributes to high blood hemolysis. The reason for turbulence lies in a combination of geometric and kinematic factors, in particular, a 90 degree turn of the flow in the inlet part of the impeller channels and a high circumferential speed of rotation of its channels. The hydrodynamic consequence of this is an increase in the hydraulic resistance of the pump flow path and separation of the boundary layer from the streamlined surface. As a result, the non-uniformity of the flow velocity field increases and separation flow zones appear, stimulating vortex formation and turbulence of the blood flow. The article provides the derivation of an equation for calculating the optimal diameter of the impeller D1, which does not have a bushing in the inlet. This design is typical for centrifugal blood pumps. As a criterion for the optimal value of D1, the minimum level of hydraulic resistance in the inlet zone of the pump was considered. Based on the derived formula, a graph of D1 values was constructed in the range of parameters: blood volume flow 3…6 liters per minute, speed 4000-10000 rpm. With an increase in blood flow and a decrease in the number of revolutions of the impeller, the diameter of the inlet to the impeller must be increased from 6.4 mm to 13.8 mm.

Корректировка методики пересчета газодинамических характеристик высоконапорной центробежной компрессорной ступени при изменении частоты вращения ротора

The proposed corrected method of conversion of gas-dynamic characteristics of high-pressure stage of turbocharger operating in the area of high circumferential speeds (conditional Mach numbers > 0,5) to other rotor speeds is given in the work, taking into account deviation from kinematic and dynamic similarity conditions. The method of combined control due to creation of swirling of flow in front of impeller and simultaneous change of rotation speed is considered. Analysis of experimental and theoretical results is done.

Leakage and wear characteristics of carbon seals for aero-engines

Experimental investigation has been performed to study the leakage and wear characteristics of carbon seal working at high circumferential speed. To expand the scope of application, two newly designed carbon seals were compared: #1 Carbon Seal (CS1) with the inner diameter of 136 mm and including 4 segments, #2 Carbon Seal (CS2) with the inner diameter of 212 mm and including 6 segments. Air leakage tests were firstly conducted in the Medium-speed Seal Test Rig. The pressure ratio changed from 1.04 to 2.02 with the rotating speed varying from 0 to 18300 r/min. Of paramount concern was the durability test, including 300 h running time accumulated by three different working conditions, which was separately implemented on each carbon seal. The morphology variation of the friction surface, wear and leakage were recorded. Results indicated that the leakage monotonously increases with the pressure ratio and decreases with the rotating speed. Comparing with CS1, more typical features exist on the friction surface of CS2, which are generated by more severe wear. Continually, leakage characteristics deteriorate. Furthermore, fitted formula has been educed for the life prediction of carbon seal, which could provide some supports for aero-engine design.

Evaluation of Lubrication Performance of Foil Bearings with New Texturing

Foil bearings have excellent characteristics such as a high damping performance and acceptable dimensional changes caused by installation errors and thermal expansion. However, the problem of large friction losses also occurs at the top foil under the high rotational speed required to support a shaft without any contact. In this paper, a new type of foil bearing with a surface texture on the top foil is proposed. The effects of the texture were verified by the rotational motion experimental analysis under a high circumferential speed and dry lubrication. For a bearing with dimples on the contact area, the effect of friction reduction could be observed under boundary lubrication. Moreover, it was also confirmed that the dimples adversely affected the air film formation with the sliding speed increase. For a newly designed F-grooved model, the phenomenon of an early transition from boundary lubrication to fluid lubrication can be seen. However, the friction coefficient increases at the boundary lubrication. In this study, it was also the highest friction reduction effect was confirmed at the maximum sliding speed. Furthermore, an additional friction reduction effect and a small temperature rise were obtained by combining the above textures.

Drag torque modeling at high circumferential speed in open wet clutches considering plate wobble and mechanical contact

Abstract A mathematical model is established to predict the drag torque increment due to the mechanical contact at high circumferential speed in open wet clutches. The fluid hydrodynamic actions are coupled simultaneously with the kinematic position of the tilted friction plate. The drag torque due to mechanical contact at high speed is estimated by presenting a rigid-body impact model. The calculation results are validated by experiments performed on an open multi-plate wet clutch test rig. The model calculation demonstrates that the drag torque also becomes higher with larger flow rates of lubricant at high circumferential speed.

Experimental Investigation on Unstable Vibration Characteristics of Plates and Drag Torque in Open Multiplate Wet Clutch at High Circumferential Speed

The drag torque caused by the viscous shear in open multiplate wet clutches has been studied in most available literature whose focus is placed on low circumferential speed. However, the drag torque increases drastically in the high circumferential speed range. The underlying physical principles and the influencing factors of the drag torque at high speed are still indeterminate. The present study aims to experimentally investigate the characteristics of the wobbling vibrations of plates and to characterize the effects of average clearance, flow rate of lubricant, shifting condition, and the number of friction interfaces on the drag torque at high circumferential speed. The result of the experiment reveals that the friction plate (FP) starts to wobble periodically at low circumferential speed, though the effect is insignificant. The dominant frequency of plate wobbling movements increases with the input speed. When wobbling vibrations of plates become unstable, the wobble gradually becomes nonlinear. The experiments confirm that the mechanical contacts between plates during the unstable wobbling vibration result in the drag torque rise at high circumferential speed. At high speed, the supplying flow rate of the lubricant influences the drag torque values. The rotation of separator plates (SPs) brings forward the torque rise and makes the drag torque rise smoother. By reducing the number of interfaces, the drag torque rise is delayed and the magnitude becomes smaller. Finally, a four-stage drag torque characteristic curve is illustrated to show the dominant factors of drag torque at different stages.

A Study of the Interaction between Coolant Jet Nozzle Flow and the Airflow Around a Grinding Wheel in Cylindrical Grinding

A grinding wheel rotating at high circumferential speed induces a boundary-layer airflow which possibly can detain the coolant from submerging into the grinding zone, in order to prevent thermal damage. To study the profile of the airflow, general laws of fluid dynamics are applied and the analytical results compared with results from CFD simulations. These are used to investigate the interaction of the coolant with the grinding wheel under the influence of the airflow with different coolant nozzle types and parameters. For validation high speed imaging is employed. The conclusions may help for a general understanding of the interaction between wheel-airflow-coolant.

Design of an axially concave pad profile for a large turbine tilting-pad bearing

To improve operational safety and/or achieve a higher load capacity of turbine tilting-pad bearings, an axially concave pad profile is presented. The thermal and mechanical stress of the loaded pads of a test bearing in load between pivot configuration has been analysed. Both film thickness and pressure distribution have been measured at a very high resolution. A fluid film calculation program in combination with a finite-volume-based structural mechanics program is used to simulate the deformation of a single pad under high circumferential speeds. In this context, the axial and tangential heat transfer coefficients of the pad surface, which act as boundary conditions for the calculation of the 3D temperature distribution, are determined using an optimization process. Herein, the match of predicted and measured pad temperatures is the goal. It can be shown that there must be a huge difference in heat transfer in axial and tangential direction in order to match the large measured temperature gradient in circumferential direction. Based on the measured deformed profile the program code is used to derive a concave pad profile, which will result in an axially non-arched sliding surface under the expected thermal load. Therefore, an iterative simulation procedure is used. By decreasing the axial arching of the pad and thus the large film thickness at the axial ends using an improved profile designed for a specific operation point, the minimum film thickness and maximum pad temperature can be influenced beneficially. The comparison of measurement data and calculation results shows very good agreement regarding the pad deformations. The results indicate that by axially concave profiling of the loaded pads of a large tilting-pad bearing for a specific operation point, the static characteristics in the form of temperature, film thickness and load capacity can be improved.

Influence of Workpiece Circumferential Speed in Wire Electrical Discharge Machining

In Wire Electrical Discharge Machining (WEDM) a specific wire run-off speed is applied to compensate wear and avoid wire breakage. Since the workpiece generally stays stationary and short discharge durations are applied, the relative displacement between wire and workpiece during one single discharge is very small. In Wire Electrical Discharge Dressing (WEDD), however, the workpiece rotates at very high circumferential speeds, since dressing is usually performed at grinding speeds. In this work the influence of relative speed in WEDM is assessed. Single discharge experiments were first carried out using circumferential speeds up to 80 m/s. The plasma channel was found to easily slide over the anode, creating elongated craters, and higher removal per single discharge was measured for higher relative speeds. A thermo-electrical model was used to help understand the process, showing that higher melting efficiencies can be reach as relative speeds are increased. The model was also used to predict damages to diamonds grains used in metal bonded grinding wheels. It was found that even if the plasma channel slides over a diamond due to the relative speed, graphitization is not likely to occur.

Study on decreasing tool wear in EDM due to arc spots sliding on electrodes

Abstract This paper describes a novel method to reduce tool electrode wear in electrical discharge machining (EDM) by applying the relative sliding motion between electrodes. Experimentally, it was found that the cathode spot is more likely to slide on the electrode surface than the anode spot. Heat conduction analysis showed that material removal increases once with the moving speed of the heat source when the moving speed is low. After peaking at the maximum value, the material removal starts to drop, resulting in almost no material removal with the ultimate speed. In this study, the end of a tungsten anode rod was therefore machined by a copper cathode disc rotating at a high circumferential speed. The results showed that tool electrode wear ratio decreases with increasing rotational speed.

English

Global competitive business market had brought increasing awareness to optimize the gear design. Gears have the advantage over friction and belt drives in that they are positive drive, a feature which most of the machine tools require, since exact speed ratios are essential. The design and manufacture of precision cut gears, made from materials of high strength, have made it possible to produce gears which are capable of transmitting extremely large loads at extremely high circumferential speeds with very little noise, vibration and other undesirable aspects of gear drives. The present work is to focus on investigating the combined effect of gear parameters on tangential force and dynamic tooth load of helical gear.

English

In the present era of sophisticated technology, gear design has evolved to a high degree of perfection. The design and manufacture of precision cut gears, made from materials of high strength, have made it possible to produce gears which are capable of transmitting extremely large loads at extremely high circumferential speeds with very little noise, vibration and other undesirable aspects of gear drives. Gears have been manufactured for a number of years with extensive ongoing research related to their efficiency, operational quality and durability. They are relatively complex and there is a number of design parameters involved in gear design. The design of gears requires an iterative approach to optimize design parameters, which govern both the kinematics as well as the strength performance. The present study is proposed to investigating the combined effect of gear ratio, helix angle, face width and normal module on beam strength and wear tooth load of steel alloy helical gear.

New high performance discs for turbo-molecular pumps

New high performance discs for turbo-molecular pumps have been developed based on the following concepts: o 1. Tests have shown that the compression ratio and the pumping speed are best at optical opaqueness of the discs. 2. In order to obtain the maximum compression ratios and pumping speeds very high circumferential speeds are necessary. These, however, are limited by the material strength of the blades. Discs have been found which, due to a favourable blade shape, permit a considerable increase in the number of revolutions per second, and, in addition, are optically opaque over the entire radius. The accuracy of the design concepts and analysis to make high performance discs in such a manner which are superior to all existing discs has been confirmed by experiments.

Use of scanning electron microscopy for evaluating diamond points

T I n prosthetic practice, rotary diamond instruments possess advantages for the removal of hard dental tissues, particularly when used in ultrahigh-speed equipment.lq3 Diamond instruments are suitable for the removal of the enamel, because they resist abrasion and have a longer life-span than tungsten carbide burs. There are only a few basic shapes of diamond points for ultrahigh-speed equipment. These points are all made to small dimensions in view of the extremely high circumferential speed and high efficiency. A new technique of electron microscopy, called scanning electron microscopy (SEM) , has made possible detailed examination of the surfaces of the diamond rotary instruments. An image obtained by this method is three dimensional, of high clarity, and has extraordinary depth of focus. 5-7 By means of the SEM, an investigation of diamond points disclosed (1) distinct differences in the quality of the materials and the workmanship and (2) alterations which take place after use.

Notes on dosage and excretion of quinidine sulphate: Wedd, A. M. and Hubbard, R. S.: Clifton Med. Bull. 15: 69, 1929

In Wire Electrical Discharge Machining (WEDM) a specific wire run-off speed is applied to compensate wear and avoid wire breakage. Since the workpiece generally stays stationary and short discharge durations are applied, the relative displacement between wire and workpiece during one single discharge is very small. In Wire Electrical Discharge Dressing (WEDD), however, the workpiece rotates at very high circumferential speeds, since dressing is usually performed at grinding speeds. In this work the influence of relative speed in WEDM is assessed. Single discharge experiments were first carried out using circumferential speeds up to 80 m/s. The plasma channel was found to easily slide over the anode, creating elongated craters, and higher removal per single discharge was measured for higher relative speeds. A thermo-electrical model was used to help understand the process, showing that higher melting efficiencies can be reach as relative speeds are increased. The model was also used to predict damages to diamonds grains used in metal bonded grinding wheels. It was found that even if the plasma channel slides over a diamond due to the relative speed, graphitization is not likely to occur.