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.

Wind Tunnel Performance Tests of the Propellers with Different Pitch for the Electric Propulsion System

The geometry of a propeller is closely related to its aerodynamic performance. One of the geometric parameters of a propeller is pitch. This parameter determines the distance by which the propeller moves forward during one revolution. The challenge is to select a propeller geometry for electric propulsion in order to achieve the best possible performance. This paper presents the experimental results of the aerodynamic performance of the set of propellers with different pitch values. The tests were performed in a closed-circuit subsonic wind tunnel using a six-component force balance. The analyzed propellers were 12-inch diameter twin-blade propellers that were driven by a BLDC (brushless direct current) electric motor. The tests were performed under forced airflow conditions. The thrust and torque produced by the propeller were measured using a strain gauge. The analysis was performed for different values of the advance ratio which is the ratio of freestream fluid speed to propeller tip speed. Additionally, a set of electrical parameters was recorded using the created measurement system. The propeller performance was evaluated by a dimensional analysis. This method enables calculation of dimensionless coefficients which are useful for comparing performance data for propellers.

METHODOLOGIES TO PREDICT HYDRODYNAMIC CHARACTERISTICS OF PUSHER AND PULLER PODDED PROPULSORS IN OBLIQUE FLOWS

This paper presents the outcome of a numerical simulation based research program to evaluate the propulsive characteristics of puller and pusher podded propulsors in a straight course and at static azimuthing conditions while operating in open water. Methodologies to predict the propeller thrust and torque, and pod forces and moments in three dimensions using a Reynolds-Averaged Navier Stokes (RANS) solver at multiple azimuthing conditions and pod configurations are presented. To obtain insight into the reliability and accuracy of the results, grid and time step dependency studies are conducted for a podded propulsor in straight-ahead condition. The simulation techniques and results are first validated against measurements of a bare propeller and a podded propulsor in straight ahead condition for multiple loading scenarios and in both puller and pusher configurations. Next, simulations were carried out to model the podded propulsors in the two configurations at multiple loading conditions and at various azimuthing angles from +30° to –30° in 15° increments. The majority of the simulations are carried out using both steady state and unsteady state conditions, primarily to evaluate the effect of setup conditions on the computation time and prediction accuracy. The predicted performance characteristics of the pod unit using the unsteady RANS method were within 1% to 5% of the corresponding experimental measurements for all the loading conditions, azimuthing angles and pod configurations studied. The non-linear behaviour of the performance coefficients of the pod unit are well captured at various loading and azimuthing conditions in the predicted results. This study demonstrates that the RANS solver, with proper meshing arrangement, boundary conditions and setup techniques can predict the performance characteristics of the podded propulsor in multiple azimuthing angles, pod configurations and in the various loading conditions with a same level of accuracy as experimental results. Additionally, the velocity and pressure distributions on and around the pod-strut- propeller bodies are discussed as derived from the RANS predictions.

STUDY ON PROPULSIVE PERFORMANCE OF TWO GEOMETRICALLY SIMILAR PODDED PROPULSORS

This paper presents the outcome of a research to evaluate the effect of size on the propulsive performance of podded propulsors in cavitating and non-cavitating open water conditions. Two cases are examined, namely: propeller-only case and pod-unit case. In the propeller-only case, a commercial propeller dynamometer is used to measure the thrust and torque of two propellers of different size at the four quadrants of propellers with varied shaft and flow speeds. Also, both propellers are tested at different tunnel pressure to study and compare the behaviour under similar cavitation conditions. In the pod-unit case, two geometrically similar but different sized pod-units are tested using two separate custom-made pod dynamometer systems in two towing tank facilities in straight-ahead and static azimuthing conditions. The study showed that the performance characteristics stabilize at lower Reynolds Number for the smaller propeller than the larger propeller. The propulsive performance of the two propellers was comparable in the four-quadrant experiments. Also, the experiments at the cavitating conditions showed that the cavitation characteristics of the two propellers were consistent at corresponding operating conditions. The experiment results of the two pod-units were also comparable for forces and moments in the three coordinate directions in the straight-ahead and static azimuthing conditions. A brief discussion on the uncertainty assessments for each of the measurements is also presented.

Influence of Various Stator Parameters on the Open-Water Performance of Pump-Jet Propulsion

In order to improve the hydrodynamic performance of pump-jet propulsion (PJP) when matching stator with the rotor, the RANS method with SST k-ω turbulence model is employed to study the influence of six kinds of stator parameters, which are classified into three groups, i.e., stator solidity, stator angles and rotor–stator spacing (S). Results show that the stator solidity involves the blade number (Ns) and chord length (L), has an obvious acceleration effect at and after stator, and produces a higher thrust and torque with a slight efficiency change. Further comparing Ns and L results, we find greater distinctions between the two cases when stator solidity is greatly adjusted. Three stator angles, i.e., stagger angle (α), lean angle (γ), and sweep angle (β), are studied. The α has the biggest effect on the thrust, torque, and efficiency; meanwhile, it shifts the advance number that corresponds to maximum efficiency. The effect of γ is similar to α, but its influence is far less than α. However, there is little difference between various β cases except for off-design conditions, where the efficiency drops dramatically as β increases. The S has a slight effect on PJP performance. Even though S decreases 34% relative to the original PJP, the rotor thrust and torque increase by less than 1%. In addition, we compare torque balance locations under various parameters, and each component force is analyzed in detail to explain the reason for performance variation. The present work is conducive to future optimization in PJP design.

Experimental Study on the Influence of Water and Cavitation on Propeller Load during Ice-Propeller Milling

When the ice-class propeller sails in an icy sea, it is affected by external factors such as water, ice, and cavitation, and the process of mutual interference is extremely complicated. In order to study the influence of water and cavitation on propeller load during the ice-propeller milling process, a test platform for ice–water propeller milling action was constructed. The load and cavitation of the propeller and single blade were measured during ice-propeller milling in air and water (atmospheric pressure and decompression conditions). Simultaneously, the changes in the load and bearing force of the propeller and blade were studied at different working conditions. The results show that, in the process of ice–water propeller milling, the direction of the propeller thrust generated by the water is opposite to that of the axial force generated by ice; the combined action of the two causes propeller thrust loss, whereas the combined action of water and ice increases propeller torque. The presence of water increases the thrust, torque, and bearing force of the fluctuating amplitude of the blade. The occurrence of cavitation reduces the thrust and torque of the propeller and blade and increases thrust fluctuating amplitudes while decreasing the tangential force fluctuating amplitude of the blade.

Determining the Aerodynamic Characteristics of a Propeller-Driven Anti-UAV Fighter While Designing Air Propellers

Given the rising importance of unmanned aerial vehicles (UAVs), this article addresses the urgent scientific problem of determining the aerodynamic characteristics of a UAV while laying out the propellers for the wings. We discuss the methodology for experimental wind-tunnel studies of aircraft configurations with propellers. It is shown that a characteristic feature of the configuration small-elongation wing with propellers is the absence of elements that are not affected by propellers. This feature makes it difficult to implement and automate a wind tunnel experiment, since there are problems with providing similar criteria for a working propeller; it is difficult to achieve perfect balancing for solid drive propellers, which causes vibration, the level of which depends on uncontrolled factors; the inability to neglect the presence of the body elements influence to the blades of propellers; the difficulty of direct measuring propeller thrust and torque. The presented methodology involves the integrated usage of experimental and numerical methods to eliminate the difficulties in conducting physical experiments in a wind tunnel. This approach makes it possible to combine the high credibility of experimental data in the study of the physical essence of phenomena with high efficiency and accuracy in determining aerodynamic characteristics by numerical methods. Using this approach, we established dependences of the aerodynamic characteristics of the small-elongation wing configuration with counter-rotating propellers on the geometric and kinematic parameters of the configuration for other extensions and constrictions of the wings. These data can serve as the basis for the development of recommendations for the selection of sensible geometric parameters of the aerodynamic configuration of a small-elongation wing with counter-rotating propellers.

Research on the Influence of Shear Turbulence on the Aerodynamic Loads Characteristics of Wind Turbine

In order to accurately analysis the aerodynamic loads characteristics of the wind turbine under different turbulent wind conditions, the horizontal homogeneity in the flow field without a wind turbine and the numerical accuracy of the homogeneous flow field with a wind turbine were validated against the experimental results. The aerodynamic loads of the wind turbine were studied under the conditions of the uniform wind with a uniform turbulence intensity, the uniform wind with a shear turbulence intensity, the shear wind with a uniform turbulence intensity and the shear wind with a shear turbulence intensity. The results show that the increasing turbulence intensity leads to a small reduction in the torque of the wind turbine. Compared with uniform wind, shear inflow leads to a sine or cosine variation in the aerodynamic performance of the wind turbine and a reduction in the wind turbine’s thrust and torque. Compared with uniform turbulence intensity, shear turbulence intensity leads to a reduction in the wind turbine’s thrust and torque, and a more obvious phase lag effect, but it has little influence on the yawing moment and pitching moment.

Surrogate models for the blade element momentum aerodynamic model using non-intrusive Polynomial Chaos Expansions

In typical industrial practice based on IEC standards, wind turbine simulations are computed in the time domain for each mean wind speed bin using a few number of unsteady wind seeds. Software such as FAST, BLADED or HAWC2 can be used to capture the unsteadiness and uncertainties of the wind in the simulations. The statistics of these aeroelastic simulations output are extracted and used to calculate fatigue and extreme loads on the wind turbine components. The minimum requirement of having six seeds does not guarantee an accurate estimation of the overall statistics. One solution might be running more seeds; however, this will increase the computation cost. Moreover, to move beyond Blade Element Momentum (BEM) based tools toward vortex/potential flow formulations, a reduction in the computational cost associated with the unsteady flow and uncertainty handling is required. This study illustrates the unsteady wind aerodynamic statistics' stationary character based on the standard turbulence models. This character is shown based on the output of NREL 5MW simulations. Afterwards, we propose a non-intrusive Polynomial Chaos Expansion approach to build a surrogate model of the loads' statistics, NREL 5MW rotor thrust and torque, at each time step, to estimate the extreme statistics more accurately and efficiently.

Investigation on Thrust and Torque Generation During Drilling of Hybrid Laminates Composite with Different Stacking Sequences Using Multiobjective Optimization Module

This paper highlights the reinforcement of two different fibers in the manufacturing of hybrid laminate composites. The feasibility of glass and carbon fiber-based hybrid composites is proposed for various high performances due to their versatile mechanical properties. However, anisotropic and non-homogeneity nature creates several machining challenges for manufacturers. It can be regulated through the selection of proper cutting conditions during the machining test. The effect of process constraints like spindle speed (rpm), feed rate (mm/min), and stacking sequences ([Formula: see text] was evaluated for the optimum value of thrust force and Torque during the drilling test. The cost-effective method of hand layup has been used to fabricate the composites. Four different hybrid composites were developed using different layers of carbon fiber and glass fiber layers. The outcomes of variables on machining performances were analyzed by variation of feed rate and speed to acquire the precise holes in the different configurations. The application potential of the proposed composites is evaluated through the machining (drilling) efficiency. The optimal condition for the drilling procedure was investigated using the multiobjective optimization-Grey relation analysis (MOO-GRA) approach. The findings of the confirmatory test show the feasibility of the MOO-GRA module in a machining environment for online and offline quality control.