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International Journal of Rotating Machinery
Journal Prestige (SJR): 0.193  Citation Impact (citeScore): 1 Number of Followers: 2  Open Access journalISSN (Print) 1023-621X - ISSN (Online) 1542-3034 Published by Hindawi  [339 journals]
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- Research on Elastic Composite Cylindrical Roller Bearing Contact Fatigue
Based on the Subsurface Stress
Abstract: In order to study the elastic contact fatigue problems of composite cylindrical roller bearing, through the three stages of contact fatigue crack initiation, propagation, and ablating of cylindrical roller bearing theoretically analyzed, the subsurface stress is one of the factors of contact fatigue damage. By finite element method and theoretical analytic method with solid cylindrical roller bearing contact surface, the size and distribution of shear stress are analyzed, and comparing the calculation results of two methods, the comparison results show that the finite element method to calculate the bearing contact problem is scientific and reasonable. Through the finite element method of cylindrical roller bearing and elastic composite cylindrical roller bearing subsurface shear stress and equivalent stress on the surface of numerical analysis, the calculation results show that the subsurface stress value of elastic composite cylindrical roller bearings was 31.65% smaller than that of ordinary cylindrical roller bearings, and the distribution of the maximum subsurface stress value of elastic composite cylindrical roller bearings was shallower than that of cylindrical roller bearings. The elastic composite cylindrical roller bearings have significant advantages over cylindrical roller bearings in terms of subsurface stress and have stronger resistance to contact fatigue damage. The finite element method is used to analyze the subsurface stress of elastic composite cylindrical roller bearings with different filling degrees. The results show that the subsurface shear stress and equivalent stress values of elastic composite cylindrical roller bearings with filling degrees of 55% to 65% are maintained at a relatively low level, and the depth of the maximum stress is minimal, which is basically distributed on the surface of the rolling body. The magnitude and distribution of subsurface stresses in elastic composite cylindrical roller bearings provide a reference for more reasonable structural design.
PubDate: Wed, 17 May 2023 09:50:01 +000
- Energy-Conserved Hydrodynamic Lubricated Components with Wall Slippage
Abstract: The hydrodynamic thrust slider and journal bearings as well as hydrodynamic lubricated gears with the merit of energy conservation by the wall slippage are reviewed. The principle for designing these hydrodynamic contacts is to artificially set the wall slippage on the stationary surface in the hydrodynamic inlet zone. To design the wall slippage on the moving surface in the hydrodynamic outlet zone can also give additional benefits. The technical merits of these mechanical components are the improved load-carrying capacity and the lowed friction coefficient, i.e., the energy conservation due to the wall slippage. Owing to the designed wall slippage, the carried load of the hydrodynamic step bearing can be increased by 200%~400% while its friction coefficient can be reduced by 50%~85%, and the load-carrying capacity of the hydrodynamic journal bearing can be increased by nearly 100% while at the same time, its friction coefficient can be reduced by more than 60%. For hydrodynamic lubricated gear contacts, by covering ultrahydrophobic or oilphobic coatings on the slower moving surface, the friction coefficient can be approaching to vanishing and the contact load-carrying capacity can be increased very significantly for large slide-roll ratios under medium or heavy loads.
PubDate: Thu, 13 Apr 2023 05:05:00 +000
- A Synchronous Machine Transient Model Based upon an Algebraic Loop
Accounting for Nonlinearity and Cross-Magnetization
Abstract: The purpose of this paper is to carry out an alternative to the present transient models for field wound synchronous machines, which is able to take into account the nonlinearity of the magnetic materials as well as the cross-magnetization. After presenting the principal model structures according to the state variables, a model based on two lookup tables for the magnetizing flux linkages is introduced and built step by step. The resulting signal flowchart shows an algebraic loop within the model, where the main flux linkage rapidly converges to its instantaneous value by simple iteration. The proof of this convergence is given for both saturated and unsaturated machine. Even though the proposed model uses the total linkage flux as state variable, as many alternative models do, it does not require the inversion of the current to flux linkage function (i.e., of lookup tables). This can spare a heavy computational task, especially with very large lookup tables. In the proposed model, the computational effort in the worst case scenario is reduced to few iterations (
PubDate: Sat, 18 Feb 2023 08:05:01 +000
- A Comparative Study of Impeller Modification Techniques on the Performance
of the Pump as a Turbine
Abstract: The extensive use of the pump as a turbine (PAT) for micro-hydropower applications has a significant value from economic and technical viewpoints. However, the unavailability of the characteristics curve and relatively lower efficiency are the two basic limitations when considering pumps for power-generating applications. In this paper, the performance of the PAT is analyzed using the computational fluid dynamics (CFD) software called Ansys CFX in conjunction with standard -. Then, experiments were done to verify the results of the simulation. Measurement inaccuracy effects are also taken into account. The initial performance of the PAT is refined by controlling basic design parameters (i.e., increasing the number of impeller blades, decreasing blade thickness, blade tip rounding, and adjusting blade inlet angle). Additionally, a new modification method known as blade grooving is also introduced in this research. Finally, all listed modification techniques are applied simultaneously to achieve maximum performance. The output of the study confirms that the adopted modification techniques have a positive effect on performance improvement. When the number of impellers is increased, the power output is enhanced by 5.72%, and blade grooving provides the most efficiency improvement, i.e., 7.00%. But decreasing blade thickness has no remarkable impact on the performance; the power output and efficiency are improved by 1.24% and 2.60%, respectively. The maximum performance improvement was achieved when the modification techniques are applied simultaneously with 10.56 and 10.20 percent of power and efficiency increments, respectively. From the entire study, it can be concluded that the chosen design parameters have an important effect on stabilizing the internal flow, decreasing the required head, decreasing the hydraulic loss in the impeller, and increasing the overall performance. The study also helps to figure out which modification technique is the most practical.
PubDate: Mon, 14 Nov 2022 09:05:00 +000
- Film Effectiveness Downstream the Trenches with Tilted Target Wall
Abstract: Film cooling is a commonly-accepted effective way to protect the gas turbine hot sections from the high temperature products of the combustion chamber. Numerous film hole geometries have been the subject of investigation by many researchers over the past three decades with the aim of keeping the target wall under the maximum allowable temperature with the least amount of precious cooling air and minimum aerodynamic losses. In this study, we are proposing a new trench geometry that is fed by 30°-inclined embedded circular film holes entering from the trench sidewall. The cooling jets impinge on the opposite wall of the trench which is tilted towards the jets and then is pushed over the coverage wall by the main flow. Three trench geometries with the same exit area and tilt angles (the angle between the trench side- and top-wall) of 75°, 90°, and 105° degrees are tested for three blowing ratios of 0.5, 0.75, and 1.0, and the film effectiveness results are compared using the adiabatic pressure sensitive paint technique. CFD analyses are also performed using the realizable turbulence model with the enhanced wall function option. Major conclusions of this study were that the trench geometry with the trench tilt angle of 75°, corresponding to the smallest trench volume, had the best performance at the lowest blowing ratio, and good agreement was observed between the CFD and test results.
PubDate: Fri, 07 Oct 2022 05:20:01 +000
- Study on Contact Force and Vibration Characteristics of Composite
Cylindrical Roller Bearing
Abstract: The composite cylindrical roller is composed of a hollow cylindrical roller and a filler body and is a new type of structure roller bearing. In order to explore the influence of different parameters on the contact characteristics and vibration characteristics of bearings, finite element models of static contact, modal analysis, and harmonic response analysis of composite cylindrical roller bearings were established based on ABAQUS software. The effects of filling rate, radial force, and the number of rollers on parameters such as contact force, contact stress, and natural frequency were studied. The results show that when the filling rate of the cylindrical roller increases from 0% to 70%, the natural frequency of bearing and the peak frequency of its harmonic response decrease, the force distribution in the contact area is also more uniform, and the maximum contact stress of the roller is reduced by 29.1%; the radial force has no effect on the peak frequency of the harmonic response of the bearing, but the increase of the radial force will increase the peak value of the response displacement, and the contact force and stress of the rollers will also increase. When the number of rollers increases from 11 to 15, the natural frequency and the peak frequency of harmonic response increase, the peak displacement decreases, the contact force distribution of the rollers in the bearing area is more uniform, and the maximum contact stress of the roller is reduced by 21.1%. The research result can provide a theoretical reference for the structural optimization and engineering application of elastic composite cylindrical roller bearings.
PubDate: Fri, 07 Oct 2022 04:20:01 +000
- Dusting Hole Film Cooling Heat Transfer on a Transonic Turbine Blade Tip
Abstract: Investigated is a transonic turbine blade tip with a squealer rim and a squealer recess, with a single dusting film cooling hole contained within the leading edge region of the squealer recess. Data are provided for transonic flow conditions for a range of film cooling blowing ratios for two tip gap values, using a linear cascade, with no relative motion between the blade and the casing. Surface heat transfer characteristics are measured using the transient impulse-response measurement approach, employed with infrared thermography. Line-averaged adiabatic film cooling effectiveness values, for the 1.4 mm tip gap, are generally very small along the pressure side rim, with only small, locally increased values along the suction side rim. For the 0.8 mm tip gap, line-averaged adiabatic film cooling effectiveness values are generally somewhat higher along the pressure side rim and along the suction side rim. In general, effectiveness values for both tip gap values, for these locations, and for the recess region, increase as the blowing ratio increases. As the tip gap decreases from 1.4 mm to 0.8 mm, line-averaged adiabatic film cooling effectiveness generally increases on the rims and downstream regions of the recess, with increased magnitudes which are spread over larger spatial surface areas. For tip gaps of 0.8 mm and 1.4 mm, for regions where the line-averaged heat transfer coefficient ratio deviates significantly from 1.00, values generally decrease as the blowing ratio increases. Across every region of the blade, line-averaged heat transfer coefficient ratios either decrease or remain approximately invariant, as the tip gap value decreases from 1.4 mm to 0.8 mm.
PubDate: Thu, 06 Oct 2022 06:35:01 +000
- Effects of Diffusion Film Hole Exit Area on the Film Cooling Effectiveness
Abstract: One popular method for the protection of gas turbines’ hot sections from high-temperature combustor gases is film cooling. Substantial amounts of research have been conducted to accomplish this task with the minimum cooling flow, maximum surface coverage, and minimal aerodynamic inefficiencies or structural penalties. In this study, a combined experimental and numerical investigation was conducted on three selected film-cooling hole geometries. These geometries were designed with the same initial metering (feed) section, a cylindrical hole of 30° inclination angle, followed by three different forward expansion section geometries. The expansion sections had a 7° laid-back angle and a 17° expansion angle in each lateral direction. However, different interior corner radii were used to blend the metering hole to the exit area, creating three different expansion geometries with almost the same exit areas. In practice, this variation in expansion geometry could represent manufacturing faults or tolerances in laser drilling of the film holes. This study shows that the variations in film-cooling effectiveness are not significant even though the expansion geometries are significantly different. The Pressure Sensitive Paint (PSP) technique was used to obtain the detailed distribution of film-cooling effectiveness on the surface area downstream of these film holes. Adiabatic film cooling effectiveness was measured at blowing ratios of 0.5, 1.0, and 2.0. CFD models of these film holes were also run, and the results were compared with the test data. The major conclusions of this study were that these proposed new geometries produced higher film effectiveness than the conventional 7°-7°-7° diffusion film holes, for the same exit area, the expansion section geometry of the film holes did not have a significant effect on the film coverage, and the numerical results were in good agreement with the test data.
PubDate: Sat, 17 Sep 2022 13:05:01 +000
- Analysis for Hydrodynamic Wedge-Platform Thrust Slider Bearing with
Ultralow Surface Separation
Abstract: For the case of ultralow surface separation, in a hydrodynamic wedge-platform thrust slider bearing, the outlet zone and a portion of the inlet zone are in boundary lubrication, while most of the inlet zone is in the multiscale lubrication contributed by both the adsorbed boundary layer and the intermediate continuum fluid film. The present paper first presents the mathematical derivations for the generated pressure and carried load of this bearing based on the governing equation for boundary lubrication and the multiscale flow equation. Then, the full numerical calculation is carried out to verify the analytical derivations. It was found that the mathematical derivations normally have considerable errors when calculating the hydrodynamic pressure distribution in the bearing, owing to introducing the equivalent parameter which is constant in the inlet zone; however they can be used to calculate the carried load of the bearing when the surface separation in the outlet zone is sufficiently high. The study suggests the necessity of the numerical calculation of the hydrodynamic pressure and even the carried load of this bearing. It is also shown that owing to the fluid-bearing surface interaction, the pressure and carried load of this bearing are significantly greater than those calculated from the classical hydrodynamic theory.
PubDate: Thu, 18 Aug 2022 04:20:01 +000
- Modelling of Hydroabrasive Erosion in Pelton Turbine Injector
Abstract: Sand particle-led erosion in the turbine parts of hydropower projects (excluding storage type projects) based on Himalaya-originated Rivers is one of the key operational challenges for concerned hydropower stations. Researchers have made multiple attempts to understand the nature of erosion and its combating technique by using numerical and experimental modelling techniques. This study relates to numerical and experimental modelling of sand particle-led erosion in the injector of the most preferred high head turbine, i.e., the Pelton turbine, followed by a comparative analysis of both techniques. This article attempts to compare erosion qualitatively and quantitatively, thus adding to the current state of the art of turbine erosion modelling. The results direct that the erosion-prone area is the needle seat in the nozzle and the region between the needle tip and nozzle exit in the needle, similar to findings reported by authors performing field setting research. The innovative aspect of the study is that by mapping the shape of the initial and eroded needle, mass lost in the erosion-prone area (as indicated by numerical erosion modelling) is calculated and compared against numerical modelling results. With the Oka erosion model employed for numerical modelling, the error in computation is about 31%. The nature of erosion in a partially open injector reveals that erosion in the needle increases with the nozzle’s partial opening. Nozzle erosion spreads away from the needle seat to the whole nozzle body. As commonly understood, the erosion of turbine parts gives rise to mechanical vibrations (especially in rotating parts) and energy loss. Numerical modelling results of injector erosion’s effect on jet energy are also presented. With uniformly spread erosion of 0.5 mm in both the needle and nozzle, loss in jet energy is 5.63%.
PubDate: Sun, 31 Jul 2022 08:35:00 +000
- Dust Removal Mechanism of the Vibrating String Filter with Charged Water
Mist
Abstract: The traditional dust removal technology is difficult to meet the strict requirements of environmental protection, so it is of practical significance and research value to study how to purify fine dust in workshop. Fine dust can be suspended in the atmosphere, while reducing the air quality. Excessive inhalation of dust may result in disease. So it should be paid close attention to dust control. The water mist charging process has experienced three stages: induction charge, corona charge transition, and corona charge. When the discharge distance is 80 mm, the charge-mass ratio of droplet and the current of water mist are most affected by corona voltage. The significant impact analysis of orthogonal experiment is studied. The result of the orthogonal experiment is analyzed by the variance method. It is noted that the inlet wind speed has the highest influence, and the discharge distance has a least influence on the dust removal efficiency. The discharge distance is 80 mm, and the voltage working band is suitable for the normal voltage regulation of the electrostatic precipitator. The condensation efficiency of charged droplets on dust is beneficial to reduce the negative effect of excessive wind speed on wet vibrating string grid and to improve the effective handling volume of dust collector. The charge-mass ratio of water mist is improved effectively, and the dust removal efficiency is increased in the vibrating string filter with charged water mist. Theoretical analysis and experimental studies showed that the vibrating string filter with charged water mist is as a new composite efficient dust removal technology that can effectively deal with the purification of fine dust particles in the gas stream, especially in respiratory dust removal.
PubDate: Mon, 20 Jun 2022 11:05:07 +000
- Experimental and Numerical Studies of the Film Cooling Effectiveness
Downstream of a Curved Diffusion Film Cooling Hole
Abstract: Film cooling technology is a commonly used method for thermal protection of gas turbines’ hot sections. A new, shaped, film cooling hole is proposed in this study. The geometry is made of a straight-through cylindrical feed hole at an inclination angle of 30° followed by an expansion section. The expansion section is created by the rotation of the same circular hole on the inclination plane about an axis normal to that plane which passes through the center of the feed hole exit area. This shape was designed to decrease the deteriorating effects of kidney vortices by proper distribution of the coolant flow emerging from the hole exit area. Cases with four rotation angles (7°, 14°, 17.5°, and 21°) were studied both experimentally and numerically and for the blowing ratios of 0.5, 1, and 2.0. For comparisons, the commonly used 7°-7°-7° diffusion hole geometry was also tested under otherwise identical conditions. For data collection, the pressure-sensitive paint (PSP) technique was used to measure the film cooling effectiveness. Streamwise- and spanwise-averaged film effectiveness results were obtained to compare the performance of different geometries. The main conclusions were that the case of 21° rotation angle produced the highest film effectiveness and outperformed the 7°-7°-7° diffusion hole geometry.
PubDate: Mon, 09 May 2022 09:20:02 +000
- Type Synthesis Based on Modular Combination with Virtual Rotation Center
and Application
Abstract: Type synthesis of mechanical structure is of great significance to the realization of mechanism target function, systematization, and stability of mechanical device. The type synthesis method of multilinkage robot has been given high demands with increasing number of degrees of freedom and high flexibility in special occasions. In order to improve the workspace and flexibility of mechanism, this paper studies the existing type synthesis theory and proposes a type synthesis method of modular combination with virtual rotation centers. Firstly, modular units are built. Secondly, modular units are expanded according to the needed paths. In the end, the expanded modular units are combined to form the kinematic linkages. Based on the proposed method, the configuration design of the aerial working platform and the self-adaptive levelling platform is completed. The stabilities of two platforms are checked by modal analysis. The prototype products are manufactured, respectively, for further verifying validity of the method. The designed aerial working platform with virtual rotation centers can achieve 360° rotating large workspace, more compact mechanical structure, and short arrival time at the same height than the common scissor-type and mast-type aerial working platforms. The designed adaptive levelling platform is tested that ensures the levelling of the upper surface at different inclinations. The method can provide new idea for the mechanism configuration and expand the application scope of new mechanisms.
PubDate: Thu, 03 Mar 2022 09:05:01 +000
