Experimental Demonstration of Active Flow Control to Reduce Unsteady Stator-Rotor Interaction

SURFACE IMPEDANCE CONTROL FOR SOUND ABSORPTION: DIRECT AND HYBRID PASSIVE/ACTIVE STRATEGIES

This paper deals with a theoretical analysis and experiments of a non-contact active feedback control, which is based on flow and aero-dynamical control, to suppress a leakage-flow-induced vibration of translational 1DOF system. In the proposed active feedback control method, the leakage-flow-induced vibration is suppressed by using a movable plate, as an actuator, set at inlet and outlet of the passage to control fluid force acting on the controlled target and fluid flow in the passage actively. The strategy of this active control method is based on active flow and aero-dynamical control which cancels the exciting fluid force acting on the rigid body. The root locus and critical flow velocity with and without control are calculated with changing the controller gain and phase-shift to evaluate the control performance, and experiments are conducted to verify the theoretical calculations. As a result, it is indicated that the leakage-flow-induced vibration is effectively suppressed by the proposed non-contact active control method and the suppression effect is very sensitive to the phase-shift and actuator position. For the inlet flow control, the vibration is effectively suppressed when the phase-shift is positive, and for the outlet flow control, the vibration is suppressed when the phase-shift is negative. The suppression effect of the inlet flow control is greater than that of outlet flow control.

This paper presents results from active flow control experiments carried out on a single stage axial compressor. The flow under various forced conditions has been investigated using 2D 2C particle image velocimetry (PIV) on three radial planes along the blades’ span and two different operating points corresponding to the minimum mass flow at which the compressor naturally stalls, and to the lower stability limit reached with the control system activated. In particular, a control strategy using continuous blowing is compared with a pulsed one using the same injected mass flow. Comparison is performed with the base flow without control (when available), or with each other, based on the PIV results in the form of relative velocity maps or inlet/outlet flow characteristics.

An experimental investigation was performed on a three-dimensional, non-conformal turret with the goal of gaining a more detailed understanding of the spatial and temporal nature of the turret wake. The turret flow field was investigated using particle image velocimetry and dynamic surface pressure measurements, both with and without active flow control. Active flow control for the current work was applied at the leading edge of the turret aperture using steady suction and was matched to a configuration used for control of aero-optic distortions. The results of these experiments give insight into the complex, three-dimensional wake that develops as a result of the turret geometry as well as the significant changes that can be achieved with the application of active flow control, even when applied only to the aperture region of the cap geometry.

In this study, passive and active flow control methods were used together to manipulate the flow around a circular cylinder. The experiments were conducted in a wind tunnel for the Reynolds number range of 4000 and 10000 based on the diameter of the circular cylinder (D). A splitter plate was used as passive flow control device and its length was chosen to be about 3.75D. Plasma actuators were placed on the circular cylinder at a position of ±90° as an active flow control device. Combining the active and passive flow control methods, a greater reduction of the drag coefficient was achieved compared to that of the cases when using these methods separately. For Reynolds numbers of 5000 and 10000, the hybrid method gives a reduction in drag of 48% and 45%, respectively. The velocity measurements were carried out by using the hot-wire anemometry and velocity profiles were obtained in the wake region. The flow was visualized by using a smoke wire method. The results revealed that the wake region of the circular cylinder with plasma actuator and splitter plate has a narrower width than the plain cylinder and with splitter plate. Also, it can be seen from spectral analysis that the vortex shedding frequency was suppressed significantly by usage of the hybrid flow control method was used.

Five-axis milling is an important machining method for complex surface parts, and chatter is an important factor affecting its machining efficiency and quality. Stability boundary prediction can effectively optimize process parameters and avoid chattering, but it is difficult to actively improve the stability boundary. Therefore, in this paper, a research on active control of five-axis milling chatter based on piezoelectric actuators is carried out. A device for active control of chatter is designed, and a dynamic model of five-axis milling machining considering active vibration suppression is established. The fuzzy PD control method is used to simulate the chatter active control, and the effect of chatter suppression is analyzed by simulation, and the active control experiment is carried out to verify the effectiveness of the active chatter control device and method.KeywordsFive-axis millingChatterFuzzy PDActive control

In the current paper, the active flow control for enhancing vortex induced vibration (VIV) of a circular cylinder, which can be potentially applied in ocean energy harvesting, is achieved by an artificial neural network (ANN) trained through deep reinforcement learning (DRL). The flow past a circular cylinder with and without jet control located on the cylinder is numerically investigated using OpenFOAM, and the ANN is applied to learn an active flow control strategy through experimenting with different mass flow rates of the jets. According to our results, the jets on the cylinder are able to dramatically destabilize the periodic shedding of the cylinder wake, which leads to a much larger VIV and work capability of the cylinder. Through controlling the flow rate of the jets based on the observation of the instantaneous flow field, the ANN successfully increases the drag by 30.78%, and the magnitude of the fluctuation of the drag and lift coefficient by 785.71% and 139.62%, respectively, while the energy consumption of the jets is almost negligible. Furthermore, the net energy output by VIV with jet control increases by 357.63% (case of water) compared with the uncontrolled situation. The results demonstrate that the performance of the active jet control strategy established by DRL for enhancing VIV is outstanding and promising for realizing the transformation from the ocean energy to electrical energy. Therefore, it is encouraged to perform further investigations on VIV enhancement using active flow control based on DRL.

The paper gives a brief overview about the challenges and the concepts for future aeroengine applications based on microjets. Technical requirement and difficulties of the potential applications of Active Flow Control (AFC) in turbomachines are discussed. The importance of an active stabilized turbocompressor for an efficiency increase is described. Future concepts of advanced turbocompressors with the application of active and passive flow control, partially based on MEMS devices are briefly sketched. Finally, the numerical methods necessary to unveil the physical background of AFC are presented.

A computational study was performed of a flow-excited Helmholtz resonator. This setup was used to model the phenomenon that occurs when a sunroof is open, or rear passenger compartment window lowered, in an automobile. The results of the computational study were validated through comparison to experimental and numerical results found in literature. After validating the setup of the computational study, the research then focused on using methods of active flow control to reduce the sound pressure levels and fluctuations within the resonator. Specifically, this was accomplished through the use of a small elongated jet placed upstream of the resonator opening. After seeing changes in the pressure levels using this active flow control technique, the velocity of the jet was altered to study its effect on the level of pressure reduction. The final results from this computational study show the desired outcome of a reduction in pressure and it was concluded that air from the jet that is added to the boundary layer produces an effect similar to that of running the simulation at a higher free stream velocity, but without active flow control. Thus, using the jet for active flow control will provide the ability to reduce pressure levels across a spectrum of free stream velocities.

Thermal active flow control has been developed to enhance the efficiency of active flow control systems. The actuation concept is derived from gas-dynamics principles, and it is based on thermal control of the air supply. It is shown that higher air supply temperatures result in reduced mass flow rate with no degradation in active flow control performance. A computational method has been used to systematically investigate the hot air supply approach for isolated blowing actuators and fluidic oscillators. Subsequently, the thermal control concept has been computationally evaluated for airplane applications. These include enhanced control authority of a vertical tail and an airplane high-lift system, confirming the trends observed from the gas-dynamics analysis with regard to reduced actuation input as a function of supply temperature. Further confirmation of the thermal actuation concept was experimentally obtained for a bench-top actuator and a vertical-tail model in a wind-tunnel setting. The paper introduces potential approaches for system integration associated with heated supply, while highlighting the benefit of using available high-temperature sources for active flow control.

Advanced technologies such as Active Flow Control (AFC) offer the potential to revolutionize next generation aircraft design through enhancing aircraft maneuver, control, and operation. DARPA’s CRANE (Control of Revolutionary Aircraft with Novel Effectors) program seeks to incorporate AFC into an aircraft design, then build and fly an X-Plane to demonstrate the potential capabilities and benefits of AFC technology. As a performer in the Phase and Phase 1 programs, Lockheed Martin has made significant progress on the development of a full-scale, tailless aircraft with an integrated AFC system to enable unique maneuvers without the use of conventional control surfaces. The Lockheed Martin-led team developed an approach that consisted of four key activities. 1. Design Library. Developing a multi-variate aerodynamic database (design library) for Active Flow Control. This was an offline process using CFD tools and significant HPC computing resources to model the complex aerodynamics and boundary layer affects associated with AFC. Response Surface Models were developed to integrate the aerodynamic effects of AFC into the Conceptual Design Process. 2. Conceptual Design Methods. Developing new methods and tools that would properly account for the effects of AFC. This included updating Stability and Control models to determine control power required and control power available, updating flight control model simulations for implementation of AFC, updated MDAO models to incorporate the changes to aero, propulsion, mass properties, and updating Operations Analysis models to model new maneuvers and behaviors achievable with AFC. These new methods were used in conducting trade studies for the design of the AFC system, the propulsion system, and the air vehicle. 3. RPV Verification. Performing test activities that help verify and calibrate our analytical methods, as well as reducing key risks. Multiple wind tunnel tests were conducted to validate the numerical simulations and gather data to capture the forces and moments generated by the various fluidic effectors on the vehicle. A subscale, dynamically scaled RPV (Remotely Piloted Vehicle) with integrated AFC was built and flown to gather additional data on aspects of interest such as flight controls and control authority, while serving as risk reduction for the larger scale X-Plane. 4. X-Plane Design. Complete the design of an AFC-enabled X-Plane. The X-Plane will serve as validation of our methods as well as demonstrate the potential for AFC to enable new and compelling mission capabilities. The work in Phase 1 matures the X-Plane design in preparation for a Preliminary Design Review. This presentation will provide an overview of the Lockheed Martin team’s progress, while highlighting challenges, solutions developed, and lessons learned under the DARPA CRANE program.

Considering the number of applications, and the quantity of research conducted over the past few decades, it would not be an overstatement to label the piezoelectric materials as the cream of the crop of the smart materials. Among the various smart materials, the piezoelectric materials have emerged as the most researched material for practical applications. They owe it to a few key factors like low cost, large frequency bandwidth of operation, availability in many forms, and the simplicity offered in handling and implementation. For piezoelectric materials, from an application standpoint, the area of active control of vibration, noise, and flow, stands, alongside energy harvesting, as the most researched field. Over the past three decades, several authors have used piezoelectric materials as sensors and actuators, to (i) actively control structural vibrations, noise and aeroelastic flutter, (ii) actively reduce buffeting, and (iii) regulate the separation of flows. These studies are spread over several engineering disciplines—starting from large space structures, to civil structures, to helicopters and airplanes, to computer hard disk drives. This review is an attempt to concise the progress made in all these fields by exclusively highlighting the application of the piezoelectric material. The research carried out in the past five years, in the areas of modeling, and optimal positioning of piezoelectric actuators/sensors, for active vibration control (AVC), are covered. Along with this, investigations into different control algorithms, for the piezoelectric based AVC, are also reviewed. Studies reporting the use of piezoelectric modal filtering and self sensing actuators, for AVC, are also surveyed. Additionally, research on semi-AVC techniques like the synchronized switched damping (on elements like resistor, inductor, voltage source, negative capacitor) has also been covered.

Chapter 6 - Active control of thermoacoustic instability

Numerical investigations for passive and active controls on aerodynamic interactions of the rotor/wing of a tiltrotor aircraft are conducted in hovering flight. The moving embedded grid met...

With a view to finding the best approach to maximize the wind energy harvesting from wind turbines, this research has focused towards assessing the effects of different innovative modifications to wind turbines at different wind speed conditions and comparing them in terms of aerodynamic performance, economy, and environmental impact. This study illustrates strategies like, active and passive flow control, incorporation of power augmentation devices (PADs) and biomimetic approaches, have huge potential to increase the output power of both the horizontal‐axis wind turbine (HAWT) and vertical‐axis wind turbine (VAWT). Literature survey reveals that boundary layer suction method from active flow control, diffusers as PADs and inspiration from flapping flight of insects from biomimetic approach can enhance the power coefficients of the turbine by 18.08%, 96%, and 35%, respectively. Furthermore, capacity factor (CF) and economic analysis showed that turbine modifications providing high‐CFs and low cost of energy (COE) will have priorities over the others, while selecting suitable turbines in a particular region. Moreover, it is evident that combining the best modifications for each strategy (active control, passive control, PADs, and biomimetic approaches) can lead to the maximum improvement in the overall performance of the turbines in terms of energy and economy.