Research on the Performance of Pumpjet Propulsor of Different Scales

This study presents a numerical research on the open-water performance of a pumpjet propulsor at different scales. Simulations were performed by an in-house viscous CFD (Computational Fluid Dynamic) code. The Reynolds-averaged Navier–Stokes (RANS) method with SST k-w turbulence model is employed. A dynamic overset grid is used to treat the relative motion between the rotor and other parts. The numerical results are compared with the model test data and they agree well. Comparisons for the open-water performance between the pumpjet propulsors with two scales are carried out. The results indicate that the total thrust coefficient of the large-scale pumpjet propulsor is greater than that of the small-scale one while the torque coefficient is smaller. Therefore, the efficiency of the large-scale pumpjet propulsor is about 8~10% higher than that of the small-scale pumpjet propulsor. The open-water performance of the rotor, pre-swirl stator and duct is obtained separately to estimate the discrepancies on the thrust and torque coefficients between different scales. To analyze the scale effect from different parts, the research on flow field and pressure distribution are carried out. The variation of total thrust and torque coefficient comes mainly from the rotor, which is caused by the flow field, influenced by the duct and stator.

Experimental Study Wind Turbine Performance of Straight-Savonius and Ice-Wind Type on the Similar proportion Aspect Ratio

The Performance of wind turbines at low speed can be improved by Ice-Wind model, particularly in self-starting conditions. Compared to a traditional wind turbine with two blades of the similar area and material, Ice-Wind can increase efficiency by 19%. Research on the Savonius turbine, particularly the Ice-Wind turbine, is challenging. It is because it has many restrictive parameters, such as the height, diameter, and area of the turbine blades. The Ice-Wind turbine shape is obtained by cutting a Savonius turbine. This process led to research on Ice-Wind turbines only under the similar parameters. The aspect ratio of a Savonius turbine has a significant effect on the speed, mechanical power and static-torque produced by the wind turbine. The research was done on Savonius and Ice-Wind turbines with the similar aspect ratio. The results show that the speed, power factor and efficiency of the Savonius turbine are higher than those of Ice-Wind. However, Savonius produces a smaller static-torque coefficient value than Ice-Wind. The results of this research contrast with other studies comparing Savonius and Ice-Wind turbines. In other researches, Savonius and Ice-Wind turbines have the similar area but different aspect ratios.

Comparative analysis of the hydrodynamic performance of pre-swirl stator pump-jet propulsor under different rotational speeds

The pump-jet propulsor(PJP) performances under various rotational speeds (20~50 r/s) are analyzed for further studying the influence of the Reynolds number (Re) on the hydrodynamics of PJP, before this, the calculation model is verified by using the experiment data, it proves the present numerical method is proper to make a further study. The results indicate both the hydrodynamic coefficients of PJP and PJP components and the contours with dimensionless variables are present high similarity, yet the Re has the slight effect on the components performance, among which, the force coefficient of rotor is the least affected, with a relative error no more than 1%. Followed is the force coefficient of rotor stator, the maximum error is 2.1%, since the force of duct and stator is so low that has the slight effect on PJP, the total force error is less than 2%. However, the torque coefficient error is bigger with a value of about 3%. Besides, it is found that all hydrodynamic coefficients vary monotonically with rotating speed, the higher Re caused by increasing the rotational speed will contribute to enhance the work ability of rotor, thus cause a lower pressure at vortex core, and change the trajectory of TLV.

Numerical Simulation and Wind Tunnel Investigation on Static Characteristics of VAWT Rotor Starter with Lift-Drag Combined Structure

In order to get rid of the impact of the global financial crisis and actively respond to global climate change, it has become a common choice for global economic development to develop clean energy such as wind energy, improve energy efficiency and reduce greenhouse gas emissions. With the advantages of simple structure, unnecessary facing the wind direction, and unique appearance, the vertical axis wind turbine (VAWT) attracts extensive attention in the field of small and medium wind turbines. The lift-type VAWT exhibits outstanding aerodynamic characteristics at a high tip speed ratio, while the starting characteristics are generally undesirable at a low wind speed; thus, how to improve the starting characteristics of the lift-type VAWT has always been an important issue. In this paper, a lift-drag combined starter (LDCS) suitable for lift-type VAWT was proposed to optimize the starting characteristics of lift-type VAWT. With semi-elliptical drag blades and lift blades equipped on the middle and rear part outside the starter, the structure is characterized by lift-drag combination, weakening the adverse effect of the starter with semi-elliptical drag blades alone on the output performance of the original lift-type VAWT and improving the characteristics of the lift-drag combined VAWT. The static characteristic is one of the important starting characteristics of the wind turbine. The rapid development of computational fluid dynamics has laid a solid material foundation for VAWT. Thus the static characteristics of the LDCS with different numbers of blades were investigated by conducting numerical simulation and wind tunnel tests. The results demonstrated that the static torque coefficient of LDCS increased significantly with the increased incoming wind speed. The average value of the static torque coefficient also increased significantly. This study can provide guidelines for the research of lift-drag combined wind turbines.

Three-dimensional computational fluid dynamic analysis of a large-scale vertical axis wind turbine

The vertical axis wind turbine (VAWT) configuration has many advantages for an offshore wind turbine Installation. In this paper, the three dimensional (3D) computational fluid dynamics analysis of a large-scale 5 MW VAWT is conducted. At the optimum tip-speed ratio (TSR), the VAWT maximum inline force was 75% larger than the maximum lateral force. It was found the dynamic stall effects cause the VAWT flow field to become increasingly asymmetrical at the mid-span plane, when the TSR is reduced. The attachment of end plates to the blade tips, resulted in a performance improvement during the upwind phase with the average blade torque coefficient in this range being increased by 4.71%. Conversely, during the blade downwind phase a reduction in performance was found due to the increase in drag from the end plates and the average blade torque coefficient in this phase was reduced by 23.1%.

Scaling of on-board characteristics of waterjet propulsion based on bench thrust testing data and loop test results

The on-board “speed-resistance-power” curves are profiled by a fitted jet thrust deduction factor relation, where the raw data are obtained from both bench thrust testing data and loop test results. Firstly, the thrust characteristics of a waterjet were tested by a thrust testing bench, while the pump performance such as capacity, head and shaft power of the waterjet was measured on a loop test rig. The useful fitted jet thrust deduction factor relation involves three related variables, that is to say, thrust coefficient, torque coefficient, and advance coefficient. Then, the best efficiency propulsion points are indicated by a collapsing technology and the subsequent results that the best efficiency propulsion points are actually existed. Cavitation margins are also noted by the two groups of data obtained by the loop data and the bench data, respectively. The discrepancy of the two margins shows the measuring error of the loop test means. In addition, the non-consistency features of the curves in the cavitation zone indicate the complex cavitation instabilities in the waterjet propulsion. At last, the bench tested thrust results are supplemented and therefore a useful map is completed.

Studi Eksperimen Pengaruh Jumlah Sudu Terhadap Kinerja Wind Turbine Crossflow

<p>Wind is an alternative energy that is environmentally friendly and sustainable. Therefore, we need a type of wind turbine that can receive wind from all directions. The crossflow type vertical axis wind turbine has a high torque coefficient at a low tip speed ratio. The purpose of this study was to determine the effect of the number of blades on the performance of the vertical axis crossflow wind turbine. The experimental test was carried out by varying the number of blades. The configuration is analyzed using the experimental wind tunnel test scheme which has been modified in the section test section. The results showed that the number of blades 16 has a power coefficient ( ) = 0.23 tip speed ratio (TSR) = 0.42 at a wind speed of 4 m / s.</p><p><strong><br /></strong></p>

DETERMINATION OF THE COMPONENTS OF THE TOTAL TORQUE NON-UNIFORMITY WHEN DISCONNECTING THE CYLINDERS

The article considers one of the topical directions of increasing fuel economy and reducing the toxicity of exhaust gases, namely, cylinder disconnection of internal combustion engines (ICE) in idling and partial loads. Current internal combustion engines with cylinder disconnection have enough technical solutions to ensure high fuel economy and ecological indicators of the engine working process. Accordingly, such engines require solution of the following tasks: improvement of mass-size indicators, cost reduction and design improvement, increase of reliability, etc. One of the main tasks of transport vehicles is also reducing the level of engine vibrations. This task is especially relevant for internal combustion engines with disconnected cylinders. When cylinders are disconnected, the unevenness of total torque increases from working processes in active cylinders and, as a result, the unevenness of the engine stroke, which affects the dynamic characteristics of the vehicle as a whole. To solve this problem, the general provisions of torsional momentum unevenness of internal combustion engines were considered. Total torsional torque of different engines was processed and data on the unevenness of torsional torque was obtained. The method of investigating the influence of cylinder switching, particularly the number of active cylinders on the unevenness of total torque is developed. The notion of torsional torque change degree with cylinder disconnection is introduced and the equation for its determination depending on the number of active cylinders is proposed. The notion of torsional torque coefficient change at disconnection of cylinders is also introduced. The application of the calculation of a four-cylinder inline engine for the possibility to compare changes in the torsional momentum unevenness when the cylinders are disconnected in the given engine was made. As a result of the calculations it was found that the torque unevenness coefficient at operation of the engine with 3, 2 and 1 cylinders in the average increases in 1,5; 2 and 3 times. The results of calculations were analyzed and histograms for all possible values of the number of active cylinders have been provided.