Wide Range Of Rotational Speeds Research Articles

Dependence of tooth flank finishing on powertrain gear noise

Finishing processes can be used in order to reduce manufacturing errors on teeth flank surfaces. These surfaces are at the heart of the gear meshing mechanics and thus should have an impact on gear noise. This paper addresses the issue of the impact tooth flank finishing on noise and vibration. The topographic and vibratory performances of two finishing processes, grinding and powerhoning, were compared. Multiscale analysis through continuous wavelet decomposition was used in order to characterize the teeth surfaces as well as the vibration spectra of a powertrain transmission tested on an industrial bench in a wide range of rotational speeds and frequencies. Results show that flank finishing processes leave their signature on the teeth surfaces which impact the vibratory behavior of the gear. Moreover, multiscale analysis approach allows the separation of vibration sources (meshing, environment, etc), and permits to quantify the impact of the choice of the finishing process.

Effects of impeller diameter and rotational speed on performance of pump running in turbine mode

The major limitations of mini/micro hydropower schemes is the higher cost of small capacity hydro turbines. Also, it is very cumbersome, time consuming and expensive to develop the site specific turbines corresponding to local site conditions in mini/micro hydro range. In such plants, small centrifugal pumps can be used in turbine mode by running in the reverse direction. The efficiency of pump as turbines (PATs) is usually lower than the conventional hydro turbines; however, there may be substantial decrease in the capital cost of the plant.Hydropower plants usually runs at part load for several months in a year due to insufficient water availability for the power generation. The application range of PAT can be widened if its part load and/or maximum efficiency can be improved. In the present study, experimental investigations are carried out on centrifugal pump running in turbine mode to optimize its geometric and operational parameters e.g. impeller diameter and rotational speed. The experiments were performed in the wide range of rotational speeds varying from 900 to 1500rpm with original (∅ 250mm), 10% trimmed (∅ 225mm) and 20% trimmed (∅ 200mm) impellers. Impeller trimming led to improvement in efficiency at part load operating conditions. The performance of PAT was found better at the lower speeds than that at the rated speed. The effects of blade rounding were studied in all the cases and it led to 3–4% rise in efficiency at rated speed with the original impeller. The empirical correlation is also developed for prediction of efficiency in terms of impeller diameter and rotational speed in non-dimensional form.

Naval Centrifugal Compressor Design Using CAD Solutions

Centrifugal compressors of turbochargersoperate in a wide range of rotational speeds, which depends on the load of the supercharged engine. Current designs of turbocharger compressors exhibit high efficiencies accompanied by high flow capacities [1]. Consequences of aerodynamic optimization are high mean stress values in the blades due to centrifugal loading as well as dynamic stresses due to blade vibrations. Blade vibrations in a turbocharger compressor are assumed to be predominantly excited by unsteady aerodynamic forces [2]. These forces are caused by a variety of sources influencing the flow. Examples include the geometry of the flow channel, elbows, the diffuser vanes or struts. Therefore, an understanding of FSI is essential for further design optimizations.

On the Influence of Traction Coefficient on the Cage Angular Velocity in Roller Bearings

The influence of different traction models on the dynamic performance of a radially loaded cylindrical roller bearing is investigated by means of a dynamic model of the bearing assembly. Two simplified traction curves along with two viscoelastic rheological models are employed to estimate the traction coefficient of MIL-L-7808-type lubricant between the roller and the races. The cage rotational speed as a function of traction forces between the roller and the races is calculated for a wide range of rotational speeds and bearing loads. Comparison of the simulation results to those of published experimental measurements reveals that the dynamic model with an appropriate viscoelastic rheological model is capable of realistically predicting the dynamic response of rolling elements under various operating conditions. However, in the case of low sliding velocities, employing a simplified traction curve may lead to acceptable results. The dynamic model was further extended to study the cage wear rate, and the results indicate that high rotational speeds and low radial loads can increase the cage wear rate due to high sliding velocities between the rollers and the races.

Performance of radial piston type reciprocating expander for CO2 refrigeration cycle

Various types of expanders have been investigated to recover a throttling loss and to improve the performance of CO2 refrigeration cycle. However, the capacity of the expander studied so far is so large that it cannot be used for a small cycle such as a vending machine, since the performance of small expander tends to get worse due to influence of leakage. In this paper, a novel reciprocating expander which can be applied to the small cycle is designed and its performance is examined. The expander has four cylinders and pistons arranged radially, and controls supply and discharge of refrigerant by a reciprocating motion of an adjacent piston. It is found that the developed expander can be operated with a small flow rate and the total efficiency attains to 0.4 over the wide range of rotational speed.

Method of calculating GTE gas-thermodynamic parameters with blade row description of an axial multistage compressor

A method of calculating the operating performance of a turboshaft gas turbine engine for steady- state conditions has been developed based on a mathematical model with a row- after- row presentation of a multistage axial compressor. This method as opposed to the existing ones makes it possible to determine gas turbine engine gas-thermodynamic parameters at different ratings taking into account such factors as air bleeding and blow off directly from the air-gas channel, the variation of geometrical parameters of compressor blade rows and meridian bypasses and changes in the programme of regulating variable stator vanes. The results of investigating the thermodynamic parameters of the main units, their elements and performance characteristics of a turboshaft gas turbine engine are presented for a wide range of rotor speeds (throttle performance). Comparisons between the computational results and the experimental data are made, their agreement is shown to be satisfactory.

The Role of Pivot Stiffness on the Dynamic Force Coefficients of Tilting Pad Journal Bearings

Recent comprehensive experimental data showcasing the force coefficients of commercial size tilting pad journal bearings has brought to rest the long standing issue on the adequacy of the [K,C,M] physical model to represent frequency independent bearing force coefficients, in particular viscous damping. Most experimental works test tilting pad journal bearings (TPJBs) with large preloads, operating over a large wide range of rotor speeds, and with null to beyond normal specific loads. Predictions from apparently simple fluid film bearing models stand poor against the test data which invariably signals to theory missing pivot and pad flexibility effects, and most importantly, ignoring significant differences in bearing and pad clearances due to actual operation, poor installation and test procedures, or simply errors in manufacturing and assembly. Presently, a conventional thermo hydrodynamic bulk flow model for prediction of the pressure and temperature fields in TPJBs is detailed. The model accounts for various pivot stiffness types, all load dependent and best when known empirically, and allows for dissimilar pad and bearing clearances. The algorithm, reliable even for very soft pad-pivots, predicts frequency reduced bearing impedance coefficients and over a certain frequency range delivers the bearing stiffness, damping and virtual mass force coefficients. Good correlation of predictions against a number of experimental results available in the literature bridges the gap between a theoretical model and the applications. Predicted pad reaction loads reveal large pivot deflections, in particular for a bearing with large preloaded pads, with significant differences in pivot stiffness as a function of specific load and operating speed. The question on how pivot stiffness acts to increase (or decrease) the bearing force coefficients, in particular the dynamic stiffness versus frequency, remains since the various experimental data show contradictory results. A predictive study with one of the test bearings varies its pivot stiffness from 10% of the fluid film stiffness to an almost rigid one, 100 times larger. With certainty, bearings with nearly rigid pivot stiffness show frequency independent force coefficients. However, for a range of pad pivot stiffness, 1/10 to ten times the fluid film stiffness, TPJB impedances vary dramatically with frequency, in particular as the excitation frequency grows above synchronous speed. The bearing virtual mass coefficients become negative, thus stiffening the bearing for most excitation frequencies.

초고속 회전체용 공기 포일 베어링의 동특성 계수 측정을 위한 전자석 가진장치에 관한 연구

Recently the requirement of long-term mobile energy source for mobile robot or small-sized unmanned vehicle is highly increased, and the micro turbine generator(MTG) which is known to have high energy and power density is under development. MTG is designed to have air foil bearing and high speed rotor of which operating speed is 400,000rpm. In the development stage of high speed rotor and bearing, stability analysis for the full operational speed range is essential and the dynamic coefficients such as stiffness and damping coefficients of bearing depending on the rotational speed are required for that. Although perturbation method is usually used to identify the dynamic coefficients, it’s not easy to give the perturbation to the high speed rotating rotor. In this study, we present the dynamic coefficients measurement system for air foil bearing which consists of electromagnets, gap sensors, high speed motor and controller. This measurement system can exert the sine sweep force to the rotor-bearing, measure the displacement of rotor and get FRF(Frequency response function) of rotor-bearing. The least square estimation method is applied to identify the dynamic coefficients of bearing from the measured frequency response at the different rpm and the identified dynamic coefficients for the wide rotational speed range are presented.

Sensorless Motor Drives with Predictive Current Control

Hardware complexity of a motor drive can be reduced by estimating controls rather than measuring using sensors. In this way the corresponding sensors are eliminated and the system becomes more robust. This article is about speed control of a sensor less induction motor with predictive current controller technique. This particular speed control technique does not require direct measurements of motor speed or motor flux. The PCC is based on a closed loop observer, which is insensitive to parameter variations. This closed loop observer calculates the required state variables over wide frequency range. This technique is more reliable even at very low frequency due to its insensitive nature against changes of motor parameters. It is proved that the drive system is applicable to the high dynamic performance and wide range of rotor speed. The obtained simulation results confirm the good properties of the proposed speed sensor less induction motor drive. Keywordspredictive current control, closed loop observer, sensorless induction motor. I. Nomenclature PCC – Predictive current controller IM – Induction motor, FOC – Field oriented control, PWM – Pulse width modulation, EMF – Electromagnetic force (back EMF) SVM – Space vector modulation, αβ – Stationary frame of references, dq – Rotating frame of references, p.u. – per unit system com – Superscript denotes commanded value, pred – Superscript denotes predicted value, ^ – Denotes value calculated in the observer, bold style font denotes vector CEMF – EMF transformation matrices, C2EMF – EMF transformation matrices, e – Motor EMF, is, ir – Stator and rotor current vector, J – Inertia, k, k-1 – Instants of calculation: actual, previous, etc., kab – Observer gain, Lr – Rotor inductance, Ls – Stator inductance, Lm – Mutual inductance, Rr – Rotor resistance, Rs – Stator resistance Timp – Inverter switching period, TL – Load torque, us – Stator voltage vector, υe – Angle position of the motor EMF vector, ρψs – Angle position of the rotor flux vector, ωr – Rotor mechanical speed, ω2 – Motor slip, I

Analysis of Particle Trajectory within Rotating Cylinders by DEM Simulation

Particle trajectory within rotating cylinders has been investigated in terms of radial positions by using the discrete element method (DEM). The dynamic information of particle groups has been obtained under a wide range of rotation speed by a method of particle marking and tracking. The results show a periodic way of inwards trend for particle motion within material bed. The period of particle motion is directly related to the rotation speed of the cylinder. However, the residence time of particles in the active layer shortens with periods, while that in the static zone prolongs. Moreover, the peak value of radial positions periodically decays, whereas the valley value periodically increases. This research laid a good foundation for further research on particle mixing and heat transport within the material bed in rotating cylinders.

A theory of Tesla disc turbines

In the present article, a mathematical theory for the flow field within a Tesla disc turbine has been formulated in the appropriate cylindrical co-ordinate system. The basis of the theory is the Navier–Stokes equations simplified by a systematic order of magnitude analysis. The presented theory can compute three-dimensional variation of the radial velocity, tangential velocity and pressure of the fluid in the flow passages within the rotating discs. Differential equations as well as closed-form analytical relations are derived. The present mathematical theory can predict torque, power output and efficiency over a wide range of rotational speed of the rotor, in good agreement with recently published experimental data. The performance of the turbine is characterized by conceptualizing the variation of load through the non-dimensional ratio of the absolute tangential velocity of the jet and the peripheral speed of the rotor. The mathematical model developed here is a simple but effective method of predicting the performance of a Tesla disc turbine along with the three-dimensional flowfield within its range of applicability. A hypothesis is also presented that it may be possible to exploit the effects of intelligently designed and manufactured surface roughness elements to enhance the performance of a Tesla disc turbine.

Transient processes in an asynchronous induction electronic excited generator with a short cut rotor

Electronic transients in an induction electronic excited generator during self-excitation and load variation have been investigated. It is shown that a generating unit with a voltage PID regulator provides stable self-excitation and voltage stability in a wide range of rotor speeds.

Vibration Analysis of a Self-Excited Vibration in a Rotor System Caused by a Ball Balancer

The ball balancer has been used as a vibration suppression device in rotor systems. It has a superior characteristic that the vibration amplitude is reduced to zero theoretically at a rotational speed range higher than the critical speed. However, the ball balancer causes a self-excited vibration near the critical speed when the balls rotate in the balancer. This self-excited vibration may occur in the wide rotational speed range with a large amplitude vibration, and in such a case, escaping from it becomes difficult. In this paper, the occurrence region and the vibration characteristics of the self-excited vibration caused by the ball balancer are investigated. The nonlinear theoretical analysis is performed and a set of the fundamental equations governing the self-excited vibration is obtained. The influences of the parameters of the ball balancer, such as, the damping of the ball’s motion, the ball’s mass, and radius of the balls’ path, are explained and they are also validated experimentally.

Experimental investigation on the performance of a lithium chloride wheel

This work has investigated the influence of change in operation conditions on the performance of a Lithium Chloride (LiCl) wheel. A rigorous experimental rig that facilitates the measurement of temperature, pressure, pressure drop, relative humidity, airflow rate and rotational speed is used. The measurements covered balanced flow at a wide range of rotational speeds (0 - 9.8 rpm), regeneration temperatures (50-70°C), airflow rates (280-540 kg/h) and relative humidities (30-65%) at ambient condition. The influence of those operation conditions on the wheel sensible effectiveness and coefficient of performance (COP) are analyzed. The result revealed that a maximum COP occurs at a rotational speed of 0.2 rpm (12 rph). The results also concluded that Kays and London correlation is sufficient in the prediction of the effectiveness of the LiCl wheel. It represents the experimental data with an average absolute percent deviation (AAPD) of 2.16 and a maximum absolute percent deviation (APDmax) of about 6.00.

Centrifugo-pneumatic valving utilizing dissolvable films

In this article we introduce a novel technology that utilizes specialized water dissolvable thin films for valving in centrifugal microfluidic systems. In previous work (William Meathrel and Cathy Moritz, IVD Technologies, 2007), dissolvable films (DFs) have been assembled in laminar flow devices to form efficient sacrificial valves where DFs simply open by direct contact with liquid. Here, we build on the original DF valving scheme to leverage sophisticated, merely rotationally actuated vapour barriers and flow control for enabling comprehensive assay integration with low-complexity instrumentation on "lab-on-a-disc" platforms. The advanced sacrificial valving function is achieved by creating an inverted gas-liquid stack upstream of the DF during priming of the system. At low rotational speeds, a pocket of trapped air prevents a surface-tension stabilized liquid plug from wetting the DF membrane. However, high-speed rotation disrupts the metastable gas/liquid interface to wet the DF and thus opens the valve. By judicious choice of the radial position and geometry of the valve, the burst frequency can be tuned over a wide range of rotational speeds nearly 10 times greater than those attained by common capillary burst valves based on hydrophobic constrictions. The broad range of reproducible burst frequencies of the DF valves bears the potential for full integration and automation of comprehensive, multi-step biochemical assay protocols. In this report we demonstrate DF valving, discuss the biocompatibility of using the films, and show a potential sequential valving system including the on-demand release of on-board stored liquid reagents, fast centrifugal sedimentation and vigorous mixing; thus providing a viable basis for use in lab-on-a-disc platforms for point-of-care diagnostics and other life science applications.

Prediction of Ingress Through Turbine Rim Seals—Part II: Combined Ingress

In Part I of this two-part paper, the orifice equations were solved for the case of externally induced (EI) ingress, where the effects of rotational speed are negligible. In Part II, the equations are solved, analytically and numerically, for combined ingress (CI), where the effects of both rotational speed and external flow are significant. For the CI case, the orifice model requires the calculation of three empirical constants, including Cd,e,RI and Cd,e,EI, the discharge coefficients for rotationally induced (RI) and EI ingress. For the analytical solutions, the external distribution of pressure is approximated by a linear saw-tooth model; for the numerical solutions, a fit to the measured pressures is used. It is shown that although the values of the empirical constants depend on the shape of the pressure distribution used in the model, the theoretical variation of Cw,min (the minimum nondimensional sealing flow rate needed to prevent ingress) depends principally on the magnitude of the peak-to-trough pressure difference in the external annulus. The solutions of the orifice model for Cw,min are compared with published measurements, which were made over a wide range of rotational speeds and external flow rates. As predicted by the model, the experimental values of Cw,min could be collapsed onto a single curve, which connects the asymptotes for RI and EI ingress at the respective smaller and larger external flow rates. At the smaller flow rates, the experimental data exhibit a minimum value of Cw,min, which undershoots the RI asymptote. Using an empirical correlation for Cd,e, the model is able to predict this undershoot, albeit smaller in magnitude than the one exhibited by the experimental data. The limit of the EI asymptote is quantified, and it is suggested how the orifice model could be used to extrapolate the effectiveness data obtained from an experimental rig to engine-operating conditions.

Aerostatic & Aerodynamic Performance of a Herringbone Thrust Bearing: Analysis and Comparisons to Static Load Experiments

The combined effects of external pressurization and herringbone grooves are studied according to the incompressible Whipple analysis; results are examined in terms of nondimensional parameters that bring out the interaction between the action of herringbone groove self-pressurization and external pressurization through orifices. It is found that interaction is beneficial in a wide range of rotational speeds. An optimized interacting design can improve the bearing stiffness and load-carrying capacity. The herringbone grooves add to bearing stiffness and load-carrying capacity even in stationary state (rotation speed is zero) and in steady state the action of herringbone groove self-pressurization further promotes bearing performance with negligible effect on orifice pressure ratio. The orifice flow tends to be saturated ahead because of the spiral grooves in the stationary state and their herringbone self-pressurization has negligible effects on flow rate in the steady state. Herringbone grooving is found to be the preferred configuration considering the bearing stiffness, air flow, and orifice pressure ratio. These predicted trends are qualitatively substantiated by tests.

Novel Bifurcation Design for Centrifugal Microfluidic Platform With Wide Range Rotational Speed

A compact disk-based enzyme linked immunosorbent assay (CD-ELISA) is used in a wide range of applications including cancer and human immunodeficiency virus testing, drug screening, and micro-organism identification. Bifurcation design is the most important structure for microfluidic channels in CD-ELISA. In this study, a bifurcation design feasible for mass production and suitable for applications over a wide range of rotational speeds is proposed. Simulations based on two-phase flow theories along with incompressible flow theories were used in this study to confirm the feasibility of the novel design. The factors that influenced the bifurcation ratio for microfluidic channels in CD-ELISA were also investigated. The geometric length for bifurcation, opening angles, and the bifurcation shape in the middle section were varied to investigate the effects of each factor on the bifurcation ratio. From the experimental results, the factors with the greatest influence on the bifurcation ratio were the geometry of the end face of the partitioning plate and the distance from the opening end. These factors can be used as controlling factors for the design of microfluidic channels.

Experimental investigation on the sensible effectiveness of LiCl wheel

Experimental investigation on the sensible effectiveness of LiCl wheel is reported. The measurements were made for balanced flow (C* = 1) for a wide range of rotational speed 0–10 rpm, regeneration temperature of 50–70°C and airflow rate 150–550 kg/h. The results revealed that the operation rotational speed for LiCl wheel is about 5 rpm which is significantly lower that for Silica gel wheel. It is also found that the sensible effectiveness is independent of the regeneration temperature. The experimental results are also fitted to the existing correlation of Simonson et al. (ASHRAE Trans 106(1):301–310, 2000). For the range of the applicability of the correlation, most of the experimental data fit the correlation within an error band of ±5%.

다단 소형 터빈에서의 부분분사 특성에 관한 연구

본 연구에 적용된 터빈은 반경류형이며, 동익의 외경은 108 mm이다. 터빈은 1.4-4.1%의 낮은 부분분사율에서 작동하므로 익형은 축류형으로 설계되었으며 3단으로 구성되었다. 터빈에서 부분분사율과 팁간극 및 노즐유동각의 변화에 따른 성능의 변화를 측정하였다. 또한 터빈의 단수를 변경하면서 각 단수에서 발생되는 출력의 차이에 대한 측정이 이루어졌다. 본 연구의 터빈은 다양한 작동조건에서 운전되므로 넓은 작동범위에 따른 비교를 위하여 회전수를 변경하면서 탈설계 영역에서의 성능 평가가 이루어졌다. 뿐만 아니라 다양한 작동조건에 합당한 시스템의 평가를 위하여 총비오크가 얻어졌다. 아울러 소형터빈의 설계 및 성능예측을 위하여 유동해석을 수행하였으며 얻어진 예측의 결과는 실험으로 얻어진 결과와 잘 일치하였다. In this study, a radial inflow type turbine was applied and the outer diameter of the turbine rotor was 108 mm. The turbine blade on a circular plate disc was designed as an axial-type because its partial admission rate was 1.4-4.1%. The turbine consisted of three stages. The performance test has been conducted with various admission rates, tip clearances and nozzle flow angles. The turbine output power was measured on each stage. The turbine performance was obtained in a wide rotational speed range in order to compare its performance according to various operating conditions. The net specific output torque was also measured to compare its overall performance. Computational analysis was conducted for predicting turbine performance. The computed results were in good agreement with the experimental results.