Influence of Ramjets’ Water Inflow on Supercavity Shape and Cavitator Drag Characteristics

Water ramjets using outer water as an oxidizer have been demonstrated as a potential propulsion mode for underwater High Speed Supercavitating Vehicles (HSSVs) because of their higher energy density, power density, and specific impulse, but water flux changes the shapes of supercavity. To uncover the cavitator drag characteristics and the supercavity shape of HSSVs with water inflow for ramjets, supercavitation flows around a disk cavitator with inlet hole are studied using the homogenous model. By changing the water inflow in the range of 0-10 L/s through cavitators having different water inlet areas, a series of numerical simulations of supercavitation flows was performed. The water inflow flux of ramjets significantly influences the drag features of disk cavitators and the supercavity shape, but it has little influence on the slender ratio of supercavitaty. Furthermore, as the water inlet area increases, the drag coefficient of the cavitators' front face decreases, but this increase does not influence the diameter of the supercavity's maximum cross section and the drag coefficient of the entire cavitator significantly. In addition, with increasing waterflux of the ramjet, both the drag coefficient of cavitators and the maximum diameter of supercavities decrease stably. This research will be helpful for layout optimization and supercavitaty scheme design of HSSVs with water inflow for ramjets.

A Simple Method for Predicting Drag Characteristics of the Wells Turbine

The drag characteristics of the Wells turbine are difficult to be accurately predicted because of the influences of many variables. Detailed analyses about the effects of these variables on the drag characteristics educe that the most sensifive parameters to the drag characteristics are the turbine solidity of the turbine and incidence angle of airflow. In this paper, an experimental research is conducted on the pressure drop across the flat- plate rotor which is used to simulate the Wells turbine. After nondimensionalization and fitting of the experimental data, a common experiential formula is obtained. Compared with the experimental data from literature, the computational results are satisfactory. Thus, this report provides a simple and convenient method for predicting the drag characteristics of the Wells turbine and optimizing the match design between an oscillating water column and a chamber.

Lift and Thrust Characteristics of Flapping Wing Aerial Vehicle with Pitching and Flapping Motion

Development of flapping wing aerial vehicle (FWAV) has been of interest in the aerospace community with ongoing research into unsteady and low Reynolds number aerodynamics based on the vortex lattice method. Most of the previous research has been about pitching and plunging motion of the FWAV. With pitching and flapping motion of FMAV, people usually study it by experiment, and little work has been done by numerical calculation. In this paper, three-dimension unsteady vortex lattice method is applied to study the lift and thrust of FWAV with pitching and flapping motion. The results show that: 1) Lift is mainly produced during down stroke, however, thrust is produced during both down stroke and upstroke. The lift and thrust produced during down stroke are much more than that produced during upstroke. 2) Lift and thrust increase with the increase of flapping frequency;3) Thrust increases with the increase of flapping amplitude, but the lift decreases with the increase of flapping amplitude;4) Lift and thrust increase with the increase of mean pitching angle, but the effect on lift is much more than on thrust. This research is helpful to understand the flight mechanism of birds, thus improving the design of FWAV simulating birds.

Drag-reducing characteristics of cationic surfactant solution flow in copper pipe

The drag-reducing characteristics of a cationic surfactant solution flow in copper pipe have been investigated experimentally.The tested drag-reducing fluid was an aqueous solution of the cationic surfactant cetyltrimethyl ammonium chloride(CTAC).The experimental results show that the maximum drag reduction percentage reduces with the increase of fluid temperature at low concentration of CTAC,such as 100×10-6 or 150×10-6.Furthermore,the concentration and temperature changes of CTAC solution have significant influences on the drag-reducing ability.The drag-reducing effect of CTAC additives shows great potentials in the application in a district heating/cooling(DHC)system,especially for the radiant floor heating(RFH)system.

Relevance of zero lift drag coefficient and lift coefficient to Mach number for large aspect ratio winged rigid body

Synthetic analysis is conducted to the wind tunnel experiment results of zero lift drag coefficient and lift coefficient for large aspect ratio winged rigid body.By means of wind tunnel experiment data,the dynamics model of the zero lift drag coefficient and lift coefficient for the large aspect ratio winged rigid body is amended.The research indicates that the change trends of zero lift drag coefficient and lift coefficient to Mach number are similar.The calculation result and wind tunnel experiment data all verify the validity of the amended dynamics model by which to estimate the zero lift drag coefficient and lift coefficient for the large aspect ratio winged rigid body,and thus providing some technical reference to aerodynamics character analysis of the same types of winged rigid body.

Studies on Factors Influencing Hydrodynamic Characteristics of Plates Used in Artificial Reefs

As a simplified model of artificial reefs, a series of plate models punched with square or circular openings are designed to investigate the effects of openings on the hydrodynamic characteristics of artificial reefs. The models are grouped by various opening numbers and opening-area ratios. They are physically tested in a water flume or used in the numerical simulation to obtain the drag force in the uniform flow with different speeds. The simulation results are found in good agreement with the experimental measurements. By the non-dimensional analysis, the drag coefficient specified to each model is achieved and the effects of openings are examined. It is found that the key factor affecting the drag coefficient is the open-area ratio. Generally, the drag coefficient is a linear function of the open area ratio with a minus slope. The empirical formulae for the square and circular openings respectively are deduced by means of the multiple regression analysis based on the measured and numerical data. They will be good references for the design of new artificial reefs. As a result of numerical simulation, the vorticity contours and pressure distribution are also presented in this work to better understand the hydrodynamic characteristics of different models.

Effect of Peak Perforation on Flow Past A Conic Cylinder at Re=100:Drag,Lift and Strouhal Number

A flow past a circular-section cylinder with a perforated conic shroud, in which the perforation is located at the peak of the conic disturbance as the shroud installed on the cylinder and uniformly distributed with several circular holes, is numerically simulated at a Reynolds number of 100. Two factors in the perforation are taken into account, i.e. the attack angle relative to the direction of incoming flow and diameter of holes. The effect of such perforation on the drag, lift and vortex-shedding frequency is mainly investigated. Results have shown that variation of the attack angle has a little effect, especially on the drag and vortex-shedding frequency, except in certain cases due to the varied vortex-shedding patterns in the near wake. The increasing hole diameter still exhibits a little effect on the drag and frequency of vortex shedding, but really reduces the lift, in particular at larger wavelength, such as the lift reduction reaching almost 66% 68% after introducing the perforation.

Drag Reduction Effect for Hypersonic Lifting-Body Vehicle with Counterflowing Jet

This study takes the novel approach of using a counterflowing jet positioned on the nose of a lifting-body vehicle to explore its drag reduction effect at a range of angles of attack.Numerical studies are conducted at a freestream Mach number of 8 in standard atmospheric conditions corresponding to the altitude of 40 km.The effects of jet pressure ratio and flying angles of attack on drag reduction of the model are systematically investigated.Considering the reverse thrust generated from the counterflowing jet,the drag on the nose at hypersonic speeds could be reduced up to 66%.The maximum lift-to-drag ratio of the model is obtained at 6°;meanwhile,the counterflowing jet produces a drag reduction of 8.8%for the whole model.In addition to the nose,the counterflowing jet influences the drag by increasing the pressure drag of the model and reducing the skin friction drag of the first cone within 8°.The results show that the potential of the counterflowing jet as a means of active flow control for drag reduction is significant in the engineering application on hypersonic lifting-body vehicles.

THE RESEARCH OF INCREASING LIFT ANDREDUCING DRAG FOR WING-TIP SAILS

ased on Quasi-Vortex-Lattiee method, a program is presented to com-pute the aerodynamic forces for nonplanar wing with wing-tip sails. By using thisprogram, the aerodynamic force is calculated and the sails are designed for an aircraftwith rectangular wing of 8.6 aspect ratio. The calculation results show that thosewing-tip sails, whose total area is 3. 1 percent of the aircraft’s basic wing area, will haveremarkable effect on reducing induced drag, and the lift-dependent drag factor can bereduced by about 18.5 to 21 .5 percent. Wind tunnel tests are conducted in NH-2 windtunnel of Nanjing Aeronautical and Astronautical University, and the results demon-strate the correctness of the above calculation results. The influences of sail parameterson performance and handling qualities of aircraft are also analyzed.

On Aircraft Lift and Drag Reduction Using V Shaped Riblets

Reducing drag during take-off and nominal(cruise)conditions is a problem of fundamental importance in aeronautical engineering.Existing studies have demonstrated that v-shaped symmetrical riblets can effectively be used for turbulence control,with those with dimensionless depth h+=15 and dimensionless width s+=15 having the best drag reduction effect.In the present study,experimental tests have been conducted considering two models of the same size,one with smooth surface,the other with v-shaped riblets of the h+=15 and s+=15 type.The results show that for an angle of attack in the 8°~20°range(take-off stage),the maximum lift coefficient can be increased by 22%.For angle of attack between 8°and 14°,a drag reduction effect can be produced using riblets,which increases with the Reynolds number,leading to a decrease in the drag coefficient maximum of 36%.Flow visualization experiments have been carried out by means of Laser Induced fluorescence.

Study on Aerodynamic Characteristics of Supersonic Airfoil

With the invention of the aircraft, it has become much faster and larger than the original Wright Brothers aircraft. When the speed is high enough to cross the speed of sound, air conditions will be different than that in low speed due to the existence of shock wave. In this work, we introduce several numerical ways to analyze the performance of the airfoil when the speed is higher than the speed of sound. With these numerical methods, we analyzed the performance of diamond-shaped airfoil under different angles of attack and speed. With this data, engineers can choose a better airfoil to attain a lower drag coefficient as well as lift coefficient when designing a high-speed aircraft.

Drag and Lift Force Acting on a Rotational Spherical Particle in a Logarithmic Boundary Flow

The drag and lift forces acting on a rotational spherical particle in a logarithmic boundary flow are numerically studied. The effects of the drag velocity and rotational speed of the sphere on the drag force are examined for the particle Reynolds number from 50 to 300 and for the dimensionless rotational angular speed of 0≤Ω≤1.0. The influence of dimensionless roughness height Z0 of the wall is also evaluated for z0 ≤ 10. The results show that the drag forces on a sphere both in a logarithmic flow and in a uniform unsheared flow increase with the increase of the drag velocity. For 50≤Rep≤300, -↑CD increases with decreased roughness height z0. The time-averaged drag coefficient is also significantly affected by rotational speed of the sphere and roughness height zo. The lift coefficient -↑CL increases with increased rotational speed and decreases with increased roughness height.

逆向射流对高超声速升力体构型的减阻特性研究

在高超声速飞行过程中,飞行器往往会面临巨大的阻力,严重限制了其飞行性能,并增加了飞行器表面的热负荷和材料应力。针对这一问题,通过数值模拟系统地分析了射流孔数量、位置和攻角对升力体减阻性能的影响。研究结果表明,随着射流孔数量的增加,整体减阻率显著提高,有效降低了升力体头部的高压区域,但也导致四周流场的不稳定性增强。射流孔位置对激波脱体距离和“气膜”厚度具有重要影响。此外,增大攻角会导致整体减阻率下降,但对局部减阻率影响较小,同时会增加上下壁面之间的压差。进一步比较研究发现,在20 km和55 km高空条件下,这3种因素对减阻性能的影响规律保持一致。研究结果为设计高效减阻方案提供了重要参考。

气体引射对临近空间升力体飞行器气动力热影响

针对临近空间高速飞行器的降热减阻需求,采用三维数值模拟手段研究了临近空间典型升力体飞行器气动力/热特性,分析了壁面气体质量引射对气动力/热特性的影响规律和作用机理。结果表明:壁面质量引射会略微增大激波脱体距离,对激波层和速度边界层有增厚作用,降低了边界层内的速度梯度,使得表面剪切力减小,从而具有较好的减阻效果。对于典型的升力体构型,在高度为60~70 km时,壁面质量引射减阻效率均不低于47.5%;在高度为80 km时,壁面质量引射减阻效率不低于10.2%;且壁面质量引射减阻效果随攻角增大而增强,随飞行高度升高而减弱。同时,壁面引射排出的低温气体对飞行器具有隔热保护作用,因此壁面质量引射能显著降低迎风面的热流,具有较好的降热效果。

边界层和压力滞后对翼型动态失速性能的影响

为优化动态失速模型经验常数,提升动态失速发生时翼型气动性能预测精度,该文基于B-L动态失速模型,结合内蒙古工业大学风能太阳能利用技术教育部重点实验室风洞实验数据,探究压力滞后及边界层滞后时间常数对翼型动态失速性能的影响。主要结论如下:压力滞后与边界层滞后时间常数对动态升力系数的影响较大且与平均攻角有关。当平均攻角相对较小且气流处于附着流动与分离流动之间时,适当减小时间常数可使动态失速模型计算结果更接近实验值;当平均攻角相对较大,气流处于分离流动与完全分离流动时,可适当增大时间常数值。压力滞后与边界层滞后时间常数对动态阻力系数的影响不显著。动态升力系数仅在攻角逐渐减小的完全分离流动过程中,随着边界层滞后时间常数的增大而减小。

深海采矿提升硬管受力特性影响因素敏感性分析

管道提升式深海采矿系统已逐渐成为深海采矿的主流系统,其系统中提升硬管流固耦合力学特性的分析成为深海矿产开发的关键问题。以适用于6 000 m水深深海采矿系统的提升硬管为研究对象,建立包括采矿船、提升硬管、提升泵与中继站等的全系统耦合模型,对硬管运动响应进行时域分析,研究不规则波引起的船舶运动以及水动力作用、海流以及浪流耦合作用对于提升硬管力学性能的影响和各影响因素的敏感性分析。结果表明管系受轴向张力为主,采矿船在波浪影响下的大幅运动将增加张力变化范围,改变管系受力特性,是影响管系受力特性最关键的因素。

滑翔增程制导炮弹弹道特性分析与设计

滑翔增程制导炮弹与普通的舰炮相比,精度高,射程远,成本低,能够在对岸进行火力支援等方面发挥重要作用,是国家军队急需发展以应对现代化作战的重要制导武器。针对滑翔增程制导炮弹初始发射条件的选取和发动机点火时刻的设计,采用遍历性计算方法进行了分析,得到了最优发射条件和发动机点火时刻。以此为基础,采用最大最大升阻比法设计了增程弹道,仿真结果表明,以最大升阻比为原则的方案弹道结合选取适当的初始发射条件和发动机点火时刻,能够有效提高滑翔增程制导炮弹的射程,对于指导工程实践和作战运用具有重要意义。

亚临界雷诺数下串列双波浪锥柱绕流数值模拟

针对风力俘能结构布局问题,基于大涡模拟(LES)方法,在亚临界雷诺数下(Re=3900)研究有限长串列双波浪锥柱的升阻力特性及其流动结构随间距比的变化规律。结果表明:由于上游波浪锥柱的影响,下游波浪锥柱的脉动升力系数大幅增大,当间距比为3时,表面时均压力系数分布形式呈反向分布;随间距比增加,上游波浪锥柱尾流充分发展,并产生大量肋状涡撞击在下游波浪锥柱表面,下游波浪锥柱产生大的脉动升力,相较于单直圆柱提升约15.3倍,阻力系数降低约0.172。所得结果可为风力俘能结构布局提供有益参考。

螺旋扭曲升阻复合型垂直轴风力机气动性能分析

提出了一种新型升阻复合型垂直轴风力机。阻力型风轮是由双层典型的萨沃纽斯型风轮组成,而升力型风轮是由螺旋扭曲一定角度的达里厄NACA0018翼型风轮组成。阻力型风轮在内,升力型风轮在外,二者用传动轴和离合器相连接。在低风速时由阻力型风轮带动升力型风轮旋转,高风速时二者各自旋转,互不影响。首先,基于计算流体力学(Computational fluid dynamics,CFD)软件对其启动及气动性能进行了仿真,分析了风轮表面的压力和风速分布。然后,分别对复合型风力机和单达里厄型风力机的启动风速和输出功率进行了测量。结果表明:复合型风力机的启动风速要小于单达里厄型的启动风速,而输出功率的差别并不大。最后,探讨了单达里厄风力机不同风速下叶尖速比与转矩系数和风能利用率的关系,确定了在叶尖速比为1.9时可将阻力型风轮和升力型风轮分离,在风速为8 m/s且叶尖速比为3时风力机的风能利用率最高,为40.6%。

零航速下的船用多功能翼水动力分析

为了研究船用多功能翼在零航速下水动力特性和展弦比效应,采用计算流体力学(CFD)软件和动网格技术对其进行三维水动力仿真。船用多功能翼根据荷兰Rotor Swing公司推出的可伸缩尾翼稳定器产品WING Stabilizer建立的几何模型,分析其在不同展弦比、攻角和摆动周期下的升/阻力特性。仿真结果表明,对于翼面积为0.5 m^(2)的船用多功能翼,在3~5内选择其展弦比,能在提高升力的同时,产生较小的阻力。因此可以认为多功能翼与常规减摇鳍对不同,过大的展弦比会降低鳍的升阻比。