Numerical Investigation of Flow Separation Control over an NACA0018 Airfoil Using Sweeping Jet Actuator

As an active flow control technology and with the advantages of no moving components, the Sweeping jet actuator has become a hotspot in the field of flow control. However, the linear relationship between oscillation frequency and momentum coefficient in a sweeping jet actuator makes it difficult to determine the dominant factors that affect control effectiveness. Decoupling the oscillation frequency and momentum coefficient, as well as determining the control mechanism, is the focus of studying the sweeping jet actuator. In this study, a novel sweeping jet actuator is designed using synthetic jets instead of feedback channels and applied to the flow separation control of NACA0018 airfoil. This article studies the control effect under three oscillation frequencies of F+ = f × c/U∞ = 1, 10, 100 and three momentum coefficients of Cμ = 0.45%, 0.625%, 0.9%. The numerical results indicate that all three oscillation frequencies have good control effects on flow separation, and the control effect is best when F+ = 1, with the maximum lift coefficient increasing by approximately 14% compared to the other two cases. And the sweeping jet actuator has a better ability to control flow separation as the momentum coefficient increases. By decoupling the characteristics of the sweeping jet actuator and conducting numerical analysis of the flow control effect, it will promote its better engineering application in the field of flow control. .

Large-eddy simulation of shock-wave/turbulent boundary layer interaction with and without Spark Jet control

The efficiency and mechanism of an active control device ＂＇Spark Jet＂ and its application in shock-induced separation control are studied using large-eddy simulation in this paper. The base flow is the interaction of an oblique shock-wave generated by 8° wedge and a spatially-developing Ma = 2.3 turbulent boundary layer. The Reynolds number based on the incoming flow property and the boundary layer displacement thickness at the impinging point without shock-wave is 20000. The detailed numerical approaches were presented. The inflow turbulence was generated using the digital filter method to avoid artificial temporal or streamwise periodicity. The , merical results including velocity profile, Reynolds stress profile, skin friction, and wall pressure were sys- tematically validated against the available wind tunnel particle image velocimetry （PIV） measure- ments of the same flow condition. Further study on the control of flow separation due to the strong shock-viscous interaction using an active control actuator ＂＇Spark Jet＇＂ was conducted. The single-pulsed characteristic of the device was obtained and compared with the experiment. Both instantaneous and time-averaged flow fields have shown that the jet flow issuing from the actuator cavity enhances the flow mixing inside the boundary layer, making the boundary layer more resis- tant to flow separation. Skin friction coefficient distribution shows that the separation bubble length is reduced by about 35% with control exerted.

Adjusting principle of gas jet controlling inlet and numerical verification

To improve the inlet performance of a ramjet working under variable conditions,a design is proposed by controlling the inlet with jet controlling,which combines the method of reducing the sealing Mach number of the external waves and the technique of controlling inlet by jet controlling.Three inlets were designed to analyze the feasibility and a numerical simulation method was used to simulate the three inlet flow fields.The adjustment mechanism of the design was studied through analysis of the simulation results.The design was verified by comparing the performances of the three inlets.The study showed that the method of reducing the sealing Mach number of the external wave system can improve the flow coefficient when the inlet works at low Mach numbers.The technique of controlling inlet by jet controlling can homogenize inlet flow fields at high Mach numbers,reduce effective throat area and increase the total pressure recovery(TPR).Adjustable inlets controlled by jet controlling demonstrate good performance at certain working ranges.

Jet Vectoring Control Using a Novel Synthetic Jet Actuator

A primary air jet vectoring control system with a novel synthetic jet actuator （SJA） is presented and simulated numerically. The results show that, in comparison with an existing traditional synthetic jet actuator, which is able to perform the duty of either ＂push＂ or ＂pull＂, one novel synthetic jet actuator can fulfill both ＂push＂ and ＂pull＂ functions to vector the primary jet by shifting a slide block inside it. Therefore, because the new actuator possesses greater efficiency, it has potentiality to replace the existing one in various appli- cations, such as thrust vectoring and the reduction of thermal signature. Moreover, as the novel actuator can fulfill those functions that the existing one can not, it may well be expected to popularize it into more flow control systems.

Parametric analyses for synthetic jet control on separation and stall over rotor airfoil

Numerical simulations are performed to investigate the effects of synthetic jet control on separation and stall over rotor airfoils. The preconditioned and unsteady Reynolds-averaged Navier–Stokes equations coupled with a k x shear stream transport turbulence model are employed to accomplish the flowfield simulation of rotor airfoils under jet control. Additionally,a velocity boundary condition modeled by a sinusoidal function is developed to fulfill the perturbation effect of periodic jets. The validity of the present CFD procedure is evaluated by the simulated results of an isolated synthetic jet and the jet control case for airfoil NACA0015. Then, parametric analyses are conducted specifically for an OA213 rotor airfoil to investigate the effects of jet parameters（forcing frequency, jet location and momentum coefficient, jet direction, and distribution of jet arrays） on the control effect of the aerodynamic characteristics of a rotor airfoil. Preliminary results indicate that the efficiency of jet control can be improved with specific frequencies（the best lift-drag ratio at F＋= 2.0） and jet angles（40 or 75） when the jets are located near the separation point of the rotor airfoil. Furthermore, as a result of a suitable combination of jet arrays, the lift coefficient of the airfoil can be improved by nearly 100%, and the corresponding drag coefficient decreased by26.5% in comparison with the single point control case.

Separation control using synthetic vortex generator jets in axial compressor cascade

An experimental investigation conducted in a high-speed plane cascade wind tunnel demonstrates that unsteady flow control by using synthetic （zero mass flux） vortex generator jets can effectively improve the aerodynamic performances and reduce （or eliminate） flow separation in axial compressor cascade. The Mach number of the incoming flow is up to 0.7 and most tested cases are at Ma = 0.3. The incidence is 10° at which the boundary layer is separated from 70% of the chord length. The roles of excitation frequency, amplitude, location and pitch angle are investigated. Preliminary results show that the excitation amplitude plays a very important role, the optimal excitation location is just upstream of the separation point, and the optimal pitch angle is 35°. The maximum relative reduction of loss coefficient is 22.8%.

CONTROL OF TWO DIMENSIONAL JETS USING MINIATURE ZERO MASS FLUX JETS

Zero mass flux jets, synthesized by acoustic actuators, have been used for the purpose of jet mixing enhancement and jet vectoring. Zero mass flux jets composed of entirely entrained fluid allow momentum transfer into the embedding flow. In the present experiments, miniature scale high aspect ratio actuator jets are placed along the long sides and near the exit plane of a primary two dimensional jet. In different modes, the primary jet can be vectored either towards or away from the actuator jets and the jet mixing is enhanced. The disturbance of the excitation frequency is developed while the unstable frequency of the primary jet is completely suppressed.

Physical factors of primary jet vectoring control using synthetic jet actuators

A primary jet vectoring using synthetic jet actuators with different exit configurations was investigated, and the main physical factors influencing jet vectoring were analyzed and summarized. The physical factors of the pressure difference, the location and area of the lower pressure region, the component of the synthetic jet momentum and the entrainment ratio of the synthetic jet flow to primary jet flow directly control the vectoring force and the vectoring angle. Three characteristic parameters of the synthetic jet contribute to the pressure difference and the area of the lower pressure region Both the extension step and slope angle of the actuator exit have functions of regulating the location of the lower pressure region, the area of the lower pressure region, and the entrainment ratio of the synthetic jet flow to primary jet flow. The slope angle of the actuator exit has additional functions of regulating the component of the synthetic jet momentum. Based upon analyzing the physical factors of jet vectoring control with synthetic jets, the source variables of the physical factors were established. A preparatory control model of jet vectoring using synthetic jet actuator was presented, and it has the benefit of explaining the efficiency of jet vectoring using synthetic jet actuator with source variables at different values, and it indicates the optimal actuator is taking full advantage of the regulating function.

SOME RECENT PROGRESS IN STUDIES ON ACTIVE CONTROL OF WALL-JET FLOWS

Active control of wall his is important in both application and basic researches. In order to establish a solid background for the expected application,it is necessary to perform detailed studies on the base nows,on their stability characteristics and on the identification technique of coherent structures. This paper is a summarizing article rather than a detailed technical report, Its main purpose is just to introduce the recent progress in the related area.

Compound control allocation strategy of dual aero/jet vane control missile

To solve the control allocation problem of dual aero/jet vane control missile, dynamics e- quations in longitudinal plane are derived, and the structure of compound control loop is designed based on attitude autopilot. Four brief compound control allocation strategies are researched and an- alyzed. Furthermore, a new strategy called chain combination variable proportional coefficient strat- egy based on rudder effect is presented. By simulation of initial climb trajectory, the characteristics of all the strategies are researched, and the results illustrate that the new strategy can meet the re- quirement well.

Formation Control for Water-Jet USV Based on Bio-Inspired Method

The formation control problem for underactuated unmanned surface vehicles(USVs) is addressed by a distributed strategy based on virtual leader strategy. The control system takes account of disturbance induced by external environment. With the coordinate transformation, the advantage of the proposed scheme is that the control point can be any point of the ship instead of the center of gravity. By introducing bio-inspired model, the formation control problem is addressed with backstepping method. This avoids complicated computation, simplifies the control law,and smoothes the input signals. The system uniform ultimate boundness is proven by Lyapunov stability theory with Young inequality. Simulation results are presented to verify the effectiveness and robust of the proposed controller.

Jet Flapping Control with Acoustic Excitation

The dynamics of flapping motion of a rectangular jet under acoustic excitation is studied experimentally by means of hot-wire measurement and flow visualization with smoke method. The excitation sufficiently enables“phase-lock”, which permitted us to extract the organized wave motion from a background field of finite turbulent fluctuations. The mean and fluctuation velocity are investigated and focused on the excitation frequency and the Reynolds number. As the excitation frequency decreases, it was found that the jet flapping and the jet spread were enhanced. The excitation with sub-harmonic frequency has significant effects on the rectangular jet behavior. The maximum value of the periodic velocity fluctuation strongly depends on the excitation frequency.

On Switching of a Flip-Flop Jet Nozzle with Double Ports by Single-Port Control

This research deals with the oscillation mechanism of a flip-flop jet nozzle with a connecting tube, based on the measurements of pressures and velocities in the connecting tube and inside the nozzle. The measurements are carried out varying: 1) the inside diameter d of the connecting tube;2) the length L of the connecting tube and 3) the jet velocity VPN from a primary-nozzle exit. We assume that the jet switches when a time integral reaches a certain value. At first, as the time integral, we introduce the accumulated flow work of pressure, namely, the time integral of mass flux through a connecting tube into the jet-reattaching wall from the opposite jet-un-reattaching wall. Under the assumption, the trace of pressure difference between both the ends of the connecting tube is simply modeled on the basis of measurements, and the flow velocity in the connecting tube is computed as incompressible flow. Second, in order to discuss the physics of the accumulated flow work further, we conduct another experiment in single-port control where the inflow from the control port on the jet-reattaching wall is forcibly controlled and the other control port on the opposite jet-un-reattaching wall is sealed, instead of the experiment in regular jet’s oscillation using the ordinary nozzle with two control ports in connection. As a result, it is found that the accumulated flow work is adequate to determine the dominant jet- oscillation frequency. In the experiment in single-port control, the accumulated flow work of the inflow until the jet’s switching well agrees with that in regular jet’s oscillation using the ordinary nozzle.

Active Stall Control System on NACA0012 by Using Synthetic Jet Actuator

Flow separation is typically an undesirable phenomenon, and boundary layer control is an important technique for the separation problems on airfoils. The synthetic jet actuator is considered as a promising candidate for flow control applications because of its compact nature and ability to generate momentum without the need for fluidic plumbing. In the present study, an active separation control system using synthetic jets is proposed and practically applied to the stall control of the NACA0012 airfoil in a wind tunnel test. In our proposed system, the flow conditions (stalled or unstalled) can be judged by calculating from two static pressure holes on the airfoil upper surface alone. The experimental results indicate that the maximum lift coefficient increases by 11% and the stall angle rises by 4°in contrast to the case under no control. It is confirmed that our proposed system can suppress the stall on the NACA0012 airfoil and that the aerodynamic performance of the airfoil can be enhanced. The proposed system can also be operated prior to the onset of stall. Therefore, separation control is always attained with no stall for all flow fields produced by changing the angle of attack that were examined.

井下管柱熔融切割工具研制

现阶段井下管柱恶性遇卡处置效率低、处置时间长,甚至会诱发井眼附加伤害,成为制约井下作业效率及安全的主要因素。为此,研制出一种基于高温熔融的金属管柱快速切割解卡作业工具。将工具下放至目标深度后,利用锚定机构实现工具与被切割管柱的相对固定,采用电激发特制的高能铝热药柱;铝热药剂急速反应释放极量、超高温的等离子火焰;火焰由特殊设计的喷射机构引导喷射,沿径向高速喷出对管柱实施径向熔切。开展液态环境中ø127 mm加重钻杆熔切试验,验证工具井下作业的可行性。研究结果表明:锚定机构能顺利完成工具与被切割管柱的相对固定,药剂能被顺利激发,喷射机构能引导火焰高速喷射实施径向熔切。该工具可对不同厚度的管柱实施熔切作业,管柱熔切深度与装药量相关,10 kg装药量下,切割用时8 s,切割平均深度达21 mm。该工具及其技术可为井下遇卡管柱高效、安全解卡提供新的解决方案。

塑壳断路器短路分断能力提升方法研究

短路分断是断路器的核心功能,提高断路器的短路分断能力是市场的持续需求。针对有效提升塑壳断路器(Moulded Case Circuit Breaker,MCCB)短路分断能力的方法开展了研究。利用栅片电压测量分析法可以检测灭弧栅片在短路分断时切割电弧的情况,评估各灭弧栅片切割电弧的性能以及电弧在灭弧室内的动态特性,为电弧优化提供参考数据。利用有限元仿真的方法进行电磁力计算,有利于快速验证优化设计方案而免去实际的试验验证,节约产品的研发成本,缩短产品的研发周期。蒸汽喷射控制(Vapour Jet Control,VJC)产气材料的运用也能够进一步提高产品的短路分断能力。综合运用以上设计方法,能够在不会大幅增加研发成本的基础上,快速提升MCCB的短路分断能力,工程应用价值较好。

基于冷气射流的涡轮流动主动控制数值模拟

针对变循环发动机在工作过程中进行涡轮流量调节的需求,以某涡轮的第一级作为研究对象,采用三维数值模拟的方式,对在导叶上不同射流位置、射流角度、射流流量的流场进行计算。结果表明:涡轮流量调节量对于射流位置十分敏感,在喉部上游附近的流量调节量最大;加入射流后涡轮损失增加,损失主要发生在射流于壁面上的流动区域;加入射流后,沿径向的大部分导叶出口气流角增大,从轮缘至轮毂导叶出口气流马赫数先增大后减小;涡轮流量调节效果与射流角度、射流流量成正比,当射流位于喉部附近、射流角度为90°、相对射流量为5%时,涡轮进口流量改变量达到13.03%,说明利用叶片表面射流,可以达到调节涡轮流量的目的。

不同迎角下逆向喷流减阻降热特性研究

文章采用基于SST k-ω湍流模型的N-S(Navier-Stokes)方程数值模拟方法,探究不同来流迎角下,逆向喷流与钝头体同轴及不同轴时,同自由来流相互作用产生的干扰流场对减阻降热效果的影响。结果表明:与无喷流情况相比,同轴逆向喷流能有效减小钝头体的阻力系数,迎角为2°时阻力系数可减小32.53%;迎角较小时,同轴逆向喷流可有效减小壁面斯坦顿数,迎角较大时,迎风面壁面斯坦顿数较大,背风面壁面斯坦顿数大幅减小;逆向喷流与钝头体轴向夹角的变化对流场及减阻降热效果产生影响,喷流与轴线夹角增大,迎风面壁面压强逐渐减小,存在使壁面斯坦顿数峰值取得最优解的喷流角度;较同轴逆向喷流,来流迎角为5°时,壁面斯坦顿数峰值可减小9.02%,来流迎角为8°时,减阻效果最高可提升1.92%。

N-JET工法桩在超深基坑封底加固施工中的应用

承压水控制一直是深基坑施工中的难点,目前,对于深基坑的承压水的隔断工艺较为简单,主要以高成本的地下连续墙为主。为探究N-JET工法桩在基坑封底加固中应用的可行性和可靠性,文章以上海轨道交通市域线机场联络线2#风井工程为案例,介绍了N-JET技术及其在深基坑工程中的应用情况,系统总结了N-JET的设计方案、施工重难点和应对措施。研究表明,地墙及封底加固共同形成的止水体系整体对邻近铁路深基坑起到了较好的封闭效果,减小了坑内降水对沪昆高铁路基的影响,验证了N-JET工法桩在邻营深基坑施工的可行性。

Robust controller design for compound control missile with fixed bounded convergence time

A robust controller for bank to turn(BTT) missiles with aerodynamic fins and reaction jet control system(RCS) is developed based on nonlinear control dynamic models comprising couplings and aerodynamic uncertainties. The fixed time convergence theory is incorporated with the sliding mode control technique to ensure that the system tracks the desired command within uniform bounded time under different initial conditions. Unlike previous terminal sliding mode approaches, the bound of settling time is independent of the initial state, which means performance metrics like convergence rate can be predicted beforehand. To reduce the burden of control design in terms of robustness, extended state observer(ESO) is introduced for uncertainty estimation with the output substituted into the controller as feedforward compensation. Cascade control structure is employed with the proposed control law and therein the compound control signal is obtained.Afterwards, control inputs for two kinds of actuators are allocated on the basis of their inherent characteristics. Finally, a number of simulations are carried out and demonstrate the effectiveness of the designed controller.