A brief study on matrix converter for wind mill application

The wind energy is one of the low qualities because of change in direction and velocity of wind. So, the input power and the frequency will be varied which affects the operation of system. For a prescribed wind velocity, the mechanical power available from the wind turbine is function of shaft speed. The shaft speed is varying due to the change in the wind velocity; thereby change in frequency and voltage is developed at the output of the induction generator. Power electronics converters are used for stabilizing the varying parameters and to obtain a constant frequency of 50Hz. commonly used power electronic device is back-to-back converters or ACDC-AC converters which has many disadvantages like costly, bulky. Through matrix converter, the terminal voltage and frequency of the induction generator can be controlled in such a way that the wind turbine will be operating at a constant frequency of 50 Hertz.

DEVELOPMENT AND TEST OF CORN STRAW KNEADING AND CONVEYING DEVICE

Aiming at the low comprehensive utilization rate of corn straw resources, a straw kneading and cutting conveyor suitable for corn harvester was designed to improve the utilization rate of corn straw resources. The workbench module of ANSYS is used to carry out modal analysis of the two blades, and it is determined that the vibration frequency will not cause damage to the blade sweeping bore. By changing the structure of the movable blade shaft, the speed of the blade shaft can be reduced while ensuring the effect of straw crushing and collecting. In order to determine the best working parameters, three-factor and three-level orthogonal test was carried out with blade arrangement, blade shaft speed and length of feed straw as test factors, and the crushing rate of straw as evaluation index. The results show that the main factors influencing the crushing rate of straw are blade shaft speed, blade arrangement and the minor factor is the length of feed straw. Finally, the optimum combination parameters, blade arrangement, blade shaft speed 400 r/min and whole plant feed with straw, were determined. The corresponding straw crushing rate was 96.39%. The research meets the requirements of straw crushing and can provide technical scheme for comprehensive utilization of corn straw.

Advanced Engine Technologies for Turbochargers Solutions

Research in the process of internal combustion engines shows that their efficiency can be increased through several technical and functional solutions. One of these is turbocharging. For certain engine operating modes, the available energy of the turbine can also be used to drive an electricity generator. The purpose of this paper is to highlight the possibilities and limitations of this solution. For this purpose, several investigations were carried out in the virtual environment with the AMESim program, as well as experimental research on a diesel engine for automobiles and on a stand for testing turbochargers (Turbo Test Pro produced by CIMAT). The article also includes a comparative study between the power and torque of the naturally aspirated internal combustion engine and equipped with a hybrid turbocharger. The results showed that the turbocharger has a very high operating potential and can be coupled with a generator without decreasing the efficiency of the turbocharger or the internal combustion engine. The main result was the generation of electrical power of 115 W at a turbocharger shaft speed of 140,000–160,000 rpm with an electric generator shaft speed of 14,000–16,000 rpm. There are many constructive solutions for electrical turbochargers with the generator positioned between the compressor and the turbine wheel. This paper is presenting a solution of a hybrid turbocharger with the generator positioned and coupled with the compressor wheel on the exterior side.

Development and substantiation of parameters of the mechanism with flexible drive for the cutterbar of the mower of double knife stroke

This paper presents the results of experimental research on the development and substantiation of parameters and operating modes of the drive mechanism of the cutting apparatus in a mower with a double knife stroke. A structural and technological scheme of the drive mechanism of the cutting device of the segment-finger type mower has been developed, in which a double stroke of the cutting device knife is provided. Analytical relationships were obtained to determine the knife stroke, speed and acceleration. Based on the results of theoretical and experimental studies, the main parameters of the mower drive mechanism were substantiated. Based on the condition of a high-quality cut of plants, at a minimum grass cutting speed, the minimum crank shaft speed was determined. By calculation, the feed area and the load area of the cutter for normal cutting with a double cut of the knife are determined. Analytical relationships were obtained to determine the power required to drive the cutterbar of a mower with a double knife stroke. Based on the research results, the main parameters of the mower with an improved drive are substantiated. An experimental sample was made and preliminary tests of the drive mechanism were carried out, agrotechnical and energy indicators of the mower operation were determined.

Porous Gas Journal Bearings: An Exact Solution Revisited and Force Coefficients for Stable Rotordynamic Performance

Having come of age, gas film bearings enable high-speed oil-free (micro) rotating machinery with gains in efficiency and reliability, longer maintenance intervals, and a reduction in contaminants released to the atmosphere. Among gas bearing types, porous surface gas bearings (PGBs) have proven successful for 50+ years and presently are off-the-shelf mechanical elements. This paper reviews the literature on PGBs since the 1970s and reproduces an exact solution for the performance of cylindrical PGBs. Both the analytical model and an accompanying finite-element (FE) model predict the performance for two PGBs, a commercially available 76 mm diameter bearing and a smaller 25 mm diameter laboratory unit whose experimental performance is available. As expected, the FE model results reproduce the analytical predictions obtained in a minuscule computing time. For a set external supply pressure, as the radial clearance increases, the flow rate through the bearing grows until reaching a peak magnitude. The PGB load capacity is a fraction of the product of the set pressure difference (pS − pa) and the bearing projected area with a significantly large centering static stiffness evolving over a narrow region of clearances. Operation with shaft speed enhances the bearing load capacity; however, at sufficiently high speeds, significant magnitude cross-coupled forces limit the stable operation of a PGB. At constant operating shaft speed, as the whirl frequency grows, the bearing effective stiffness (Keff) increases, while the effective damping (Ceff) becomes positive for whirl frequencies greater than 50% shaft speed. Similar to a plain hydrodynamic journal bearing, the PGB is prone to a half-frequency whirl, albeit the system natural frequency can be high, mainly depending on the external supply pressure. In essence, for the cases considered, PGBs are linear mechanical elements whose load capacity is proportional to the journal eccentricity.

Simulation of a Simplified Aeroengine Bearing Chamber Using a Fully Coupled Two-Way Eulerian Thin Film/Discrete Phase Approach Part I: Film Behaviour Near The Bearing

Previous work at the Gas Turbine and Transmissions Research Centre (G2TRC) has highlighted the need for an adequate computational model that can appropriately model the oil shedding behaviour from bearings. Oil can breakup forming droplets and ligaments, subsequently forming thin and thick films driven by both gravity and shear. Our previously published work using OpenFOAM successfully coupled the Eulerian thin film model (ETFM) with the discrete phase model (DPM) [1]. In this paper, the previously developed ETFM-DPM capability is, for the first time, extended to an aeroengine representative bearing chamber configuration. The configuration matches that of a simplified aeroengine bearing chamber that has been investigated by researchers at the Gas Turbine and Transmissions Research Centre (G2TRC). Numerical investigations are conducted for three different shaft speeds: 5,000, 7,000 and 12,000 rp; at two oil flow rates: 7.3 l/min and 5.2 l/min. CFD results are validated against existing experimental data for the two lower shaft speeds. Evaluation of computed mean film thickness shows excellent agreement with the experimental data. Results show that there is a diminishing reduction of film thickness with an increasing shaft speed. The computational study allows investigation of oil residence time in the annulus near the bearing. Residence time is seen to reduce with increasing shaft speed and with increasing oil flow rate. This CFD investigation represents the first successful fully coupled two-way ETFM-DPM investigation for bearing chamber applications, establishing a firm foundation for future aeroengine bearing chamber modelling.

On the Shaft Speed Selection of Parallel Hybrid Aero Engines

The boosted turbo fan or parallel hybrid is a promising means to reduce fuel consumption of gas turbines on aircraft. With an electric drive on the low-pressure spool of the gas turbine, it requires a trade-off between the characteristics of the gas turbine and the electric power sub-systems. Reducing specific thrust at a given thrust requirement results in a larger fan with a lower pressure ratio. This leads to improved propulsive efficiency but at the expense of increased weight and nacelle drag. At a given design relative tip Mach number, increasing fan size and hence tip diameter means the fan shaft speed will need to be reduced. This will, according to occasionally quoted ‘rules of thumb’, make the directly coupled electrical drive more efficient but heavier. The objective of this paper is to expose some key aspects of this trade-off in terms of efficiency and weight, and relate them to these guidelines. The paper applies sophisticated methodology in both addressed domains. For the gas turbine, multi-point design is used. Here, established synthesis matching schemes focusing on gas turbine performance parameters are extended with parameters from the sizing and weight estimation such as diameters and tip speeds. For the electrical machine, fully analytical sizing capturing the impact of cooling supply is used. The paper reports estimated gas path and machine geometries. It gives an understanding of the interactions between both sub-systems and allows concluding which low pressure spool speed gives the best instantaneous performance. It largely confirms the quoted rules of thumb but exposes that the factors affecting machine efficiency are more involved than implied for an integrated design.

Prediction and Mitigation Strategies for Compressor Instabilities due to Large Pressurized Volumes in Micro Gas Turbine Systems

Micro gas turbines are a versatile platform for advanced cycle concepts. In these novel cycles, basic micro gas turbine components — compressor, turbine, combustor and recuperator — are coupled with various other technologies to achieve higher efficiency and flexibility. Examples are hybrid power plants integrating pressurized fuel cells, solar receivers or thermal storages. Characteristically, such complex cycles contain vast pressurized gas volumes between compressor and turbine, many times larger than those contained in conventional micro gas turbines. In fast deceleration maneuvers the rotational speed of the compressor drops rapidly. However, the pressure decrease is delayed due to the large amount of gas contained in the volumes. Ultimately, this can lead to compressor flow instability or surge. To predict and mitigate such instabilities, not only the compressor surge limit must be known, but also the dynamic dependencies between shaft speed deceleration, pressure and flow changes within the system. Since appropriate experiments may damage the system, investigations with numerical simulations are crucial. The investigation begins with a mathematical explanation of the relevant mechanisms, based on a simplified analytical model. Subsequently, the DLR in-house simulation program TMTSyS (Transient Modular Turbo-System Simulator) is used to investigate the impact of transient maneuvers on a micro gas turbine test rig containing a large pressurized gas volume in detail. After the relevant aspects of the simulation model are validated against measurement data, it is shown that the occurrence of compressor instabilities induced by fast deceleration can be predicted with the simulator. It is also shown that the simulation tool enables these predictions using only measurement data of non-critical maneuvers. Hence, mitigation strategies are derived that allow to estimate save shaft speed deceleration rate limits based on non-critical performance measurements.

Effect of Pad Material, Copper vs. Steel, on the Performance of a Tilting Pad Journal Bearing: Measurements and Predictions

High temperature operation limits the life of fluid film bearings; hence the need to quantify the effect of pad material on the performance of tilting pad journal bearings (TPJBs). The paper presents measurements of performance conducted on a copper-pads bearing (C-PB) and a steel-pads bearing (S-PB). Both bearings have the same geometry and differ on the pads’ backing material, copper vs. steel, and slightly in the assembled cold clearance. The journal diameter D = 102 mm, and a bearing has five pads with length L = 0.4D, nominal radial clearance 0.064 mm, and pad preload of 0.42. The pads are 12.3 mm in thickness and have a 50% offset pivot, ball-in-socket type. The bearings operate at four shaft speeds ranging from 6 krpm (32 m/s surface speed) to 14 krpm (74 m/s) and under multiple specific loads ranging from 0.17 MPa to 2.1 MPa. ISO VG 32 oil, at a supply temperature of 49 °C, lubricates a test bearing configured with end seals (flooded bearing). At the highest load (on pad) and low shaft speed, the S-PB static eccentricity is up to 37% higher than that for the C-PB. The oil exit temperature rise is similar for both bearings, the maximum difference reaches 6 °C. For all operating conditions, the pads’ peak temperature rise, having a maximum difference of 5 °C to 16 °C, is larger for the S-PB. The S-PB produces a ∼ 5% lower drag power loss than that in the C-PB. Drag power in both bearings increases with shaft speed and is largely independent of applied load. From dynamic load tests with multiple excitation frequencies to 250 Hz, the C-PB direct stiffness KYY (along the load direction) is up to 30% higher than the S-PB stiffness, while the difference in KXX between the C-PB and the S-PB ranges from 60% to 90%. Similar to the stiffness results, the C-PB produces larger direct damping coefficients; CYY and CXX are up to 25% and 40% larger than those for the S-PB. Both bearings, however, show symmetry in the damping coefficients, i.e., CXX ∼ CYY. Virtual mass coefficients (MXX, MYY) are significant in magnitude though having a large uncertainty. A computational physics model predicts the TPJB performance under identical conditions. The exhaustive comparison conducted with a sound dimensional characterization of parameters reveals that predictions agree well with measurements of journal eccentricity, oil exit temperature, pad surface temperatures, and stiffness and damping force coefficients. The differences amount to 20% or less. The model relies on specifying the material properties for pads and pivots and the operating (hot) clearance to produce accurate thermo-mechanically induced deformations that affect bearing performance at high loads and high surface speed operation.