Effect of air injection method on the performance of an air lift pump

Air lift pump performance was investigated experimentally for different submergence ratios (the ratio between the immersed length of the riser and its total length) using different air injection footpiece designs. For this purpose an air lift pump with a riser 200 cm long and 2.54 cm in diameter, was designed and tested. Nine different air injection footpiece designs were used at four submergence ratios with different air injection pressures (from 0.2 to 0.4 bar). An area of 10 mm² was chosen and divided into nine injection hole arrangements (1, 2, 3, 4, 6, 15, 25, 34 and 48 holes) to cover the whole experimental range. Four submergence ratios were used for this work: 0.75, 0.7, 0.6 and 0.5. The experimental results showed a marked effect on the pump performance when operated with different types of injectors at different submergence ratios. The results indicated that the disk with three holes (D3) gives the highest efficiency at nearly all submergence ratios. Moreover, it is found that there is a suitable disk design for maximum water flow rate at every submergence ratio. Further, the highest efficiency resulted at the largest used submergence ratio, namely 0.75. The pump capacity and efficiency were found to be functions of air flow rate, lift ratio, and injection pressure.     

太空环境压力变化对液浮陀螺性能的影响分析

对太空气压变化影响液浮陀螺性能的机理进行了理论分析,然后利用有限元分析法对陀螺仪在压力变化时浮子产生的变形进行了计算.明确了压力变化对陀螺仪结构件变形的影响程度,并从几个对陀螺仪漂移产生影响的主要方面进行了深度分析,得知压力变化导致浮子的结构变形是陀螺仪性能变化的主要因素,其中框架的变形引起的陀螺漂移达0.3((°)·h-1),g.最后通过对某型陀螺仪进行压力变化试验,验证了分析结果的正确性.此外还对陀螺仪进行了封闭波纹管的实验.得出结论:采用相对厚实的结构,刚度较大、稳定性好的材料可大大提高陀螺仪对环境的适应性,另外还可以给陀螺仪装上对外界环境的密封隔离装置.     

Effect of frequency of air flow on the performance of the Wells turbine

Experimental investigations on the effect of Strouhal number and rotor solidity on the performance of 0.2m diameter Wells self rectifying air turbine with NACA 0021 profile blades are presented. The results show an increase in starting torque with the Strouhal number of airflow and rotor solidity. The effect of Strouhal number on the running performance of the turbine is solidity dependent     

Effect of blade profile on the performance of the Wells self-rectifying air turbine

The effect of blade profile and thickness on the starting and running performance of a 0.2 m diameter Wells turbine is reported. The starting torque can be increased considerably by using thicker NACA aerofoils and modified NACA aerofoil blades and by increasing the turbine solidity. Thicker and modified NACA aerofoil blades also improved the running performance of the turbine. Artificially roughened blades showed degraded performance.     

Topology optimization and heat dissipation performance analysis of a micro-channel heat sink

Junction temperature in the electronic packaging process is one of the critical factors affecting the service life of electronic devices. A micro-channel heat sink is a common heat dissipating device used to reduce the thermal resistance between components and substrate. In order to maximize the heat dissipation while minimizing the pressure drop, this paper adopts a topology optimization method. A material interpolation method based on variable density principle is used together with a moving asymptote algorithm for the optimization. The physics is governed by the heat and mass transfer, coupled with the momentum conservation in the fluid. Four parameters are varied in order to investigate their influence on the optimization process. A three-dimensional geometry has been constructed to study the flow field and the results are compared to a reference case to verify the temperature uniformity and thermal performance of the model. It is demonstrated that the optimized design of the micro-channel heat sink is reliable and effective.     

Engine performance analysis and optimization of a dual-mode scramjet with varied inlet conditions

A dual-mode scramjet can operate in a wide range of flight conditions. Higher thrust can be generated by adopting suitable combustion modes. Based on the net thrust, an analysis and preliminary optimal design of a kerosene-fueled parameterized dual-mode scramjet at a crucial flight Mach number of 6 were investigated by using a modified quasi-one-dimensional method and simulated annealing strategy. Engine structure and heat release distributions, affecting the engine thrust, were chosen as analytical parameters for varied inlet conditions(isolator entrance Mach number: 1.5–3.5). Results show that different optimal heat release distributions and structural conditions can be obtained at five different inlet conditions. The highest net thrust of the parameterized dual-mode engine can be achieved by a subsonic combustion mode at an isolator entrance Mach number of 2.5. Additionally, the effects of heat release and scramjet structure on net thrust have been discussed. The present results and the developed analytical method can provide guidance for the design and optimization of high-performance dual-mode scramjets.     

基于线性鲁棒性优化的弦支结构设计及分析

结构的鲁棒性是指结构抵抗不相称破坏的能力。目前,研究集中于框架类结构鲁棒性的评价,缺少弦支结构鲁棒性评价及设计方法。首先基于H∞理论,采用结构系统传递函数的H∞范数作为结构鲁棒性的定量评价指标。然后,采用SIMP模型描述建立了人工材料模型,以结构线性鲁棒性为优化目标,将结构鲁棒性设计转化成连续体拓扑优化,并通过粒子群算法求解。以弦支双曲球壳模型为例,通过鲁棒设计得到了鲁棒构形。最后通过作用超越静荷载,制造干扰场景,分析不同结构设计方案的非线性鲁棒性。结果表明,H∞结构鲁棒性评价指标可以反映干扰与后果是否相称,通过连续体拓扑优化进行鲁棒设计,能够有效地提高结构鲁棒性,可以为弦支结构初始概念设计提供参考。     

Effect of skin flexibility on aerodynamic performance of flexible skin flapping wings for micro air vehicles

Experimental Techniques - As part of the ongoing research on micro air vehicles, the present work focuses on the effect of membrane flexibility on the aerodynamic performance of flexible latex...     

Investigation on the planform and kinematic optimization of bio-inspired nano air vehicles for hovering applications

Wing shape and kinematics of flapping wing nano air vehicles are two important factors in their design process. These factors require an optimal design in terms of decreasing the needed aerodynamic power. Since, insects are regarded as the best natural flier in hovering flight, seven of their wings are considered in order to determine the best wing shape for hovering applications. Because of the difference in the original bio-inspired shape of these wings, two scenarios are studied, namely, considering the same wingspan and same wing surface. Using the quasi-steady approximation to model the aerodynamic loads and a basic gradient approach to optimize the kinematics of the wing, the optimum Euler angles, required aerodynamic power, and hence the best wing shape for each scenario are analytically determined. The results show that the wing shape and surface strongly impact the aerodynamic characteristics and performances of the chosen wing shapes. It is demonstrated that the twisted parasite wing shape is a good candidate to minimize the required aerodynamic power during hovering. The strategy used in this analysis can be used to evaluate the performance of any realistic wing shape design and could provide a guideline for selecting the best wing shape and kinematics for flapping wing nano air vehicles with hovering capabilities.     

Theoretical considerations on shock reflections and their implications on the evaluation of air intake performance

Many theoretical studies have shown the existence of a hysteresis effect in the solution of oblique shock reflections. In fact, a wide domain of free-stream Mach number and shock angle values exists where regular reflection and Mach reflection are both possible solutions for the same flow conditions. Part of this domain overlaps the typical operating conditions of supersonic air intakes, and therefore it is of practical interest to obtain a deeper understanding of the theoretical problem. Indeed, although both solutions are theoretically possible, they yield very different flowfields and consequently large discrepancies in the evaluation of the air intake performance. Numerical solutions for steady configurations have been carried out and compared with the flow evolution obtained for time-dependent cases. The results have confirmed numerically the existence of the multiple solution domain where hysteresis takes place in time-dependent simulations. The analysis of the physical and numerical problems encountered has provided indications for a correct simulation in practical applications. Received 10 August 1999 / Accepted 6 October 2000     

The effect of footpiece design on the performance of a small air lift pump

A small air lift pump made from 24·3 mm bore glass tube has been tested with two different air injection footpiece designs. In one (the air-jacket design), air was injected radially inwards, and in the other (the nozzle design), air was injected axially at inlet to the riser. Each design has been tested using a variety of injection hole sizes and numbers. With the air-jacket design, the pump discharge characteristic was found to be independent of the number and sizes of the injection holes. The nozzle design showed greater pumping capability at high air flow rates and with small orifice area, but the efficiency was then very low. Some comparisons with the theoretical model of Stenning and Martin (9) have been made, and the model has been extended to take account of the momentum of the air injected in the nozzle footpiece.     

Effect of gravity and tangential air resistance on unwinding cable

In the field of unwinding dynamics, most of the researches so far have only considered the normal component of air resistance. In this research, the transient-state equation of motion that accurately contains all the boundary conditions at the guide-eyelet and lift-off points is derived. The transient-state equation of motion is derived from Hamilton??s principle for an open system, because the total mass of an unwinding cable varies continuously. The virtual work in Hamilton??s principle includes gravity, normal air resistance, and tangential air resistance. The air resistances are assumed to be proportional to the square of the normal and tangential velocities, and the effects of gravity and tangential air resistance on the unwinding cable are verified on the basis of the maximum balloon radius and the associated error. The results show that the effect of gravity and tangential air resistance on the maximum balloon radius is within 4?%, which is negligible.     

锻造操作机机构受力性能的多目标优化设计

考虑到锻造操作机的重载特性,为避免因受力不均造成局部受力过大而危及机械结构的安全性,本文以某DDS锻造操作机为例,进行操作机的机构受力性能优化设计。通过灵敏度分析,以关键的机构受力构件在整个工作空间上的平均受力作为优化目标,基于多目标遗传算法NSGA II对操作机的主运动机构进行尺寸优化设计,以合理分配机构受力。与原设计相比,优化后的操作机具有更为良好的整体受力性能。本文的研究工作有助于操作机的机构设计。     

Effect of the conical-shape on the performance of vortex tube

The present study focuses on the effect of conical shape in the cold side of the Ranque-Hilsch vortex tube which is shown to have a considerable influence on the system performance. A vortex tube is a simple circular tube with no moving parts which is capable to divide a high pressure flow into two relatively lower pressure flows with temperatures higher and lower than the incoming flow. A three-dimensional computational fluid dynamic model is used to analyse the mechanisms of flow inside a vortex tube. The SST turbulence model is used to predict the turbulent flow behaviour inside the vortex tube. The geometry of a vortex tube with circumferential inlet slots as well as axial cold and hot outlet is considered. Performance curves temperature separation versus cold outlet mass fraction are calculated for a given inlet mass flow rate and varying outlet mass flow rates.     

Thermodynamics of irreversible processes and the lyapuncv-function method

A connection is established between the production of entropy in irreversible processes and the Lyapunov function of the corresponding system of equations. Thermodynamic limitations are formulated on the functions that enter in the kinetic equations. The results are illustrated with relaxation processes in viscoelastic media.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 4, pp. 99–107, July–August, 1972.     

Effects of camber angle on aerodynamic performance of flapping-wing micro air vehicle

This study investigates the unsteady aerodynamic characteristics of the cambered wings of a flapping-wing micro air vehicle (FW-MAV) in hover. A three-dimensional fluid–structure interaction solver is developed for a realistic modeling of large-deforming wing structure and geometry. Cross-validation is conducted against the experimental results obtained also in the present study to establish more accurate analyses of cambered wings. An investigation is carried out on the unsteady vortex structures around the wings caused by the passive twisting motion. A parametric study is then conducted to evaluate the aerodynamic performance with respect to the camber angle at three different flapping frequencies including normal operating conditions. The camber angles producing the largest thrust and highest propulsive efficiency are estimated at each flapping frequency, and their effects on aerodynamic performance are analyzed in terms of the stroke phase. The timing and magnitude of the passive twisting motion, which are dependent on the camber angle at the operating frequency, greatly affects the unsteady vortex structure. Consequently, the camber angle designed at the operating frequency plays a key role in enhancing the aerodynamic performance of FW-MAVs.