Fast Switching Solenoid Valves Research Articles

Experimental Investigation of Flow Control on a High-Lift Wing Using Modulated Pulse Jet Vortex Generator

In this paper, the potential of a novel active flow control strategy by means of a modulated pulse jet vortex generator to enhance high-lift performance is demonstrated on a two-dimensional supercritical National Aeronautics and Space Administration (NASA) SC(2)-0714 airfoil with a single slotted trailing-edge flap at a high deflection angle. Fast-switching solenoid valves and compressed air were used as actuators to excite the flow. The vortex generator slot pairs were incorporated into the shoulder of the trailing-edge flap, where the flow separation occurs due to the high flow deflection and severe adverse pressure gradient. In these experiments, in addition to the simple square-wave excitation signal, a burst-modulated excitation signal as a novel pulse jet sequence was implemented to produce the unsteady blowing. The burst-modulation signal was used for the first time for a fast-switching solenoid valve actuator. The experiments were performed at a freestream velocity of 25 m/s with a corresponding Reynolds number of about 1×106 for a range of angles of attack from 0° to 20° at flap deflection angles from 0° to 35°. The results indicated that the ejection from vortex generator slot pairs was able to prevent flow separation completely in most conditions. These measurements revealed that the burst-modulated excitation was accompanied by more aerodynamic improvements and less air consumption relative to the simple pulsed jet excitation. In the best flow control mode, the results showed about a 12.6% increase in the lift coefficient and a 19.8% decrease in the drag coefficient.

Pneumatic Quasi-Passive Variable Stiffness Mechanism for Energy Storage Applications

State-of-the-art compliant actuators with variable stiffness meet the requirements for exoskeletons only to a limited extent, usually due to their higher mechanical complexity and large mass. In this letter, we present a quasi-passive lightweight pneumatic mechanism that emulates stiffness modulation in the pneumatic cylinder using fast-switching valves and without the need of an air supply. Depending on the state of the valves, the mechanism can operate in different modes. For example, timely control of three fast-switching solenoid valves can modulate the internal equilibrium pressure and adjust the stiffness of the cylinder, or it can be turned off to allow free movement, which is sometimes critical in wearable robotic applications. The novel approach to stiffness modulation is mathematically described. Furthermore, we discuss how changing the initial equilibrium pressure of the mechanism affects the stiffness and energy storage capacity, which has been studied in several experiments. The experiments show successful modulation of the stiffness without the need for an external pressurized air supply. The obtained measured findings are satisfactorily consistent with the derived theoretical model.

Fluidic-Oscillator-Based Pulsed Jet Actuators for Flow Separation Control

The control of flow separation on aerodynamic surfaces remains a fundamental goal for future air transportation. On airplane wings and control surfaces, the effects of flow separation include decreased lift, increased drag, and enhanced flow unsteadiness and noise, all of which are detrimental to flight performance, fuel consumption, and environmental emissions. Many types of actuators have been designed in the past to counter the negative effects of flow separation, from passive vortex generators to active methods like synthetic jets, plasma actuators, or sweeping jets. At the Chair of Aerodynamics at TU Berlin, significant success has been achieved through the use of pulsed jet actuators (PJA) which operate by ejecting a given amount of fluid at a specified frequency through a slit-shape slot on the test surface, thereby increasing entrainment and momentum in a separating boundary layer and thus delaying flow separation. Earlier PJAs were implemented using fast-switching solenoid valves to regulate the jet amplitude and frequency. In recent years, the mechanical valves have been replaced by fluidic oscillators (FO) in an attempt to generate the desired control authority without any moving parts, thus paving the way for future industrial applications. In the present article, we present in-depth flow and design analysis which affect the operation of such FO-based PJAs. We start by reviewing current knowledge on the mechanism of flow separation control with PJAs before embarking on a detailed analysis of single-stage FO-based PJAs. In particular, we show that there is a fundamental regime where the oscillation frequency is mainly driven by the feedback loop length. Additionally, there are higher-order regimes where the oscillation frequency is significantly increased. The parameters that influence the oscillation in the different regimes are discussed and a strategy to incorporate this new knowledge into the design of future actuators is proposed.

Fluidic-Oscillator-Based Pulsed Jet Actuators for Flow Separation Control

The control of flow separation on aerodynamic surfaces remains a fundamental goal for future air transportation. On airplane wings and control surfaces, the effects of flow separation include decreased lift, increased drag, and enhanced flow unsteadiness and noise, all of which are detrimental to flight performance, fuel consumption, and environmental emissions. Many types of actuators have been designed in the past to counter the negative effects of flow separation, from passive vortex generators to active methods like synthetic jets, plasma actuators, or sweeping jets. At the Chair of Aerodynamics at TU Berlin, significant success has been achieved through the use of pulsed jet actuators (PJA) which operate by ejecting a given amount of fluid at a specified frequency through a slit-shape slot on the test surface, thereby increasing entrainment and momentum in a separating boundary layer and thus delaying flow separation. Earlier PJAs were implemented using fast-switching solenoid valves to regulate the jet amplitude and frequency. In recent years, the mechanical valves have been replaced by fluidic oscillators (FO) in an attempt to generate the desired control authority without any moving parts, thus paving the way for future industrial applications. In the present article, we present in-depth flow and design analysis which affect the operation of such FO-based PJAs. We start by reviewing current knowledge on the mechanism of flow separation control with PJAs before embarking on a detailed analysis of single-stage FO-based PJAs. In particular, we show that there is a fundamental regime where the oscillation frequency is mainly driven by the feedback loop length. Additionally, there are higher-order regimes where the oscillation frequency is significantly increased. The parameters that influence the oscillation in the different regimes are discussed and a strategy to incorporate this new knowledge into the design of future actuators is proposed.

Iterative Learning Control for Trailing-Edge Flap Lift Enhancement with Pulsed Blowing

A novel iterative learning control algorithm was developed and applied to an active flow control problem. The technique used pulsed air jets applied to a trailing-edge flap to enhance the lift. The iterative learning control algorithm used position-based pressure measurements to update the actuation. The method was experimentally tested on a two-element high-lift wing in a low-speed wind tunnel. Compressed air and fast switching solenoid valves were used as actuators to excite the flow, and the pressure distribution around the chord of the wing was measured as a feedback control signal for the iterative learning controller. Experimental results showed that the actuation was able to delay the separation and increase the overall lift by over the angle of attack range and increase from 2.7 to 3.0 compared to the nonactuated case. By using the iterative learning control algorithms, the controller was able to track the target lift, and by using an optimum control algorithm with an extended reference, the controller was able to maximize the lift enhancement.

Study of Pressure Characteristics in PWM Controlled Variable Rate Spraying System

In PWM controlled variable rate spraying system, spraying quantities were regulated by fast switching solenoid valves. However, hydraulic impacts were generated by these fast switching solenoid valves in pipe system, which affected stabilities of spraying quantities and atomization characteristics. In order to study pressure changing regularities when solenoid valves operated, then to design a pressure controller to improve spraying qualities in PWM controlled variable rate spraying system, Fluent was used to simulate pressure characteristics in the pipe system and pressure curves were drawn under the following 3 working conditions, solenoid valve opening, closing, and switching continuously with 5 Hz frequency and 50% duty ratio. Related experiments were carried out to test real pressure signals in the pipe based on a PWM controlled variable rate spraying system. Relative errors between simulation results and experiment results were below 10%. Thus, this simulation model of PWM controlled variable rate spraying system in Fluent was reliable to simulate pressure characteristics in the pipe in other common working conditions, and which contributed to design pressure controller and to optimize the whole PWM controlled variable rate spraying system.

Position control of an electro-pneumatic system based on PWM technique and FLC

In this paper, modeling and PWM based control of an electro-pneumatic system, including the four 2–2 valves and a double acting cylinder are studied. Dynamic nonlinear behavior of the system, containing fast switching solenoid valves and a pneumatic cylinder, as well as electrical, magnetic, mechanical, and fluid subsystems are modeled. A DC–DC power converter is employed to improve solenoid valve performance and suppress system delay. Among different position control methods, a proportional integrator derivative (PID) controller and fuzzy logic controller (FLC) are evaluated. An experimental setup, using an AVR microcontroller is implemented. Simulation and experimental results verify the effectiveness of the proposed control strategies.

Active flow separation control by a position-based iterative learning control algorithm with experimental validation

A novel iterative learning control (ILC) algorithm was developed and applied to an active flow control problem. The technique uses pulsed air jets to delay flow separation on a two-element high-lift wing. The ILC algorithm uses position-based pressure measurements to update the actuation. The method was experimentally tested on a wing model in a 0.9 m × 0.6 m low-speed wind tunnel at the University of Southampton. Compressed air and fast switching solenoid valves were used as actuators to excite the flow, and the pressure distribution around the chord of the wing was measured as a feedback control signal for the ILC controller. Experimental results showed that the actuation was able to delay the separation and increase the lift by approximately 10%–15%. By using the ILC algorithm, the controller was able to find the optimum control input and maintain the improvement despite sudden changes of the separation position.

Adaptive Predictive Controller for Hydraulic Systems Driven by Fast Switching On/Off Solenoid Valves

In hydraulic systems driven by fast-switching solenoid valves, the utilization of conventional adaptive predictive controllers usually requires much computational effort, and thus it is difficult to realize real-time implementations in plants using short sampling times. This paper deals with an adaptive unified predictive controller which can be implemented conveniently for hydraulic systems driven by fast-switching solenoid valves. It is clarified by experimental investigation that the amount of computational effort is considerably reduced by employing the proposed controller. It is also clarified that the controller permits convenient and easy implementation of an adaptive predictive control scheme for on/off tracking control systems.

Application of Unified Predictive Control to On/Off Control of Hydraulic System Driven by Fast-Switching Solenoid Valves

The utilization of fast-switching solenoid valves permits the construction of lowcost hydraulic systems with high resistance to oil contamination. In spite of these advantages, the use of solenoid valves results in severe nonlinearities and discontinuities in the flow rate, making it difficult to control and design the system. In this study, the performance of a hydraulic system operated by an on/off unified predictive controller was investigated. It was verified that despite strong nonlinearities in the plant, the performance of the system was considerably improved by employing the predictive control scheme.

差動ＰＷＭ法による油圧ロータリアクチュエータのディジタル制御

Ever since fast-switching solenoid valves were accepted as a powerful device for interfacing hydraulic systems with electronics, mechatronics technology for hydraulic actuators has developed rapidly. Such actuator development, however, has been mainly concentrated on linear motion actuators, as a result, the development of rotary-type actuators has still yet to reach a sufficient level.A rotary-type actuator acts as an actuator by converting hydraulic energy to mechanical rotational motion within a specified angle, having a wide necessary applications. This study deals with a vane-type rotary actuator since it is superior as regards its high torque/inertia ratio and small size. By constructing a systemin which the actuator is operated by two 3-way solenoid valves, a differential-pulse width modulation method has been adopted as the method for digital control for the system. The solenoid valves in this system act as converters of the electronic-pulse signals to hydraulic ones. An arbitrary pulse width of the pressure difference across both sides of the actuator is obtained by adjusting the switching time of each valve.The dynamic characteristics of the system were investigated by way of experiments and digital simulations. Thus it was clarified that the actuator, operated by differential-PWM, shows good linearity as a control element, achieving accurate positioning. Consequently, the availability of the system is well confirmed. Furthermore, it was recognized that the mathematical model used in this simulation might serve as a comparatively simplified model for describing the dynamics of this system.