Closed-Loop Trailing-Edge Separation Control System Using Empirical Mode Decomposition

Active Unsteady Flow Control experiments were performed on a Natural Laminar Flow, NLF 0414 airfoil at Rec = 1.0 × 10 6 . The goal of this study was to control boundary-layer separation across the trailing-edge region of the airfoil in off-design conditions. Both openloop and closed-loop control approaches were used. Active control of separation was achieved using a series of blowing slots at the x/c = 0.75 location. Open loop control parameters were varied across a parametric range of jet amplitudes, actuation frequencies and duty cycles and performance measurements were acquired to identify the effectiveness of these actuation schemes. PIV measurements were acquired across a horizontal plane near the trailing edge region of the model to understand the effects of actuation on flow separation and the vortex dynamics associated with unsteady actuation. A closed loop controller was developed to vary the actuation parameters in-situ using sensory feedback from the unsteady surface pressure measurements and adaptive modal decomposition methods. This closed-loop system was able to automatically control the extent of separation such that a desired value of Cl was obtained.

The Inductor-Convertor Bridge (ICB) is a DC-AC-DC convertor network using gate controlled thyristers which allows controllable energy transfer between two superconducting coils. Since an ICB system is asynchronous, both phase and frequency are controllable. Simultaneous open-loop phase angle control and closed-loop frequency control has been analyzed and demonstrated on a three-phase model using two 4-H superconducting coils.

The present study intends to investigate the potentiality of the single dielectric barrier discharge plasma actuators (SDBDPAs) to reattach the separated flow, occurring at low Reynolds numbers. For this aim, a curved wall plate, which profile shape was designed to reproduce the suction surface of a low-pressure turbine (LPT) blade, was installed in the test section of a closed loop wind tunnel and a SDBDPA was placed in a groove made over it, at the front of the adverse pressure gradient region. The flow behavior in absence of actuation has been experimentally investigated by particle image velocimetry (PIV) and laser Doppler velocimetry measurements (LDV). Moreover, sinusoidal voltage excitation with amplitude of 8 kV and frequency of 2 kHz was applied to the SDBDPA and PIV measurements were also performed in presence of actuation. The applied voltage and the discharge current have also been recorded simultaneously, and they have been used for the determination of the device dissipated power. Different wind tunnel free stream velocities were investigated, both in absence and presence of actuation. The effect of the active flow control was then studied in the entire measurement domain by analyzing the velocity fields, the turbulence intensity (Tu) values, the momentum coefficient (cμ) and the boundary layer shape factor (H12). In absence of actuation, a large reverse flow and a turbulence intensity up to ≈60% was observed in the separation region. Good agreement was found between the flow results obtained by the two velocity measurement techniques. Considering the actuated cases, it was found that, in all the tested operating conditions, actuation implied a reduction of the separated region and the turbulence intensity, even if a low flow control effect was noticed at the highest tested velocity.

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 study numerically investigates closed-loop control strategies for mitigating dynamic stall on a pitching National Advisory Committee for Aeronautics (NACA) 0012 airfoil using tandem dielectric barrier discharge plasma actuators. The unsteady Reynolds-Averaged Navier–Stokes equations, coupled with a transitional model and an empirical plasma body force model, are employed to simulate the complex flow physics. A closed-loop control algorithm, which activates actuators based on real-time detection of the incipient flow separation point, is developed and compared against open-loop actuation and a baseline (no-control) case. Key performance metrics, including lift-to-drag ratio enhancement, aerodynamic damping augmentation, and reattachment characteristics, are evaluated across various actuator excitation frequencies. Results demonstrate that the proposed closed-loop system effectively delays stall onset, advances flow reattachment to occur at higher angles of attack during downstroke, and significantly improves cycle-averaged aerodynamic damping up to 55.1% compared to baseline case. While both open-loop and closed-loop control improve the lift-to-drag ratio by approximately 13.4%–17.2%, closed-loop control achieves this with substantially reduced actuator power consumption by strategically activating only the most effective actuator. This work underscores the potential of intelligent, feedback-driven plasma actuation for enhancing the performance and stability of airfoils operating under aggressive unsteady conditions.

We propose a 2D generalization to the midpoint-based empirical mode decomposition algorithm (MBEMD). Unlike with the regular bidimensional empirical mode decomposition algorithm (BEMD), we do not interpolate the upper and lower envelopes, but rather directly find the mean envelope, utilizing well defined points between two extrema of different kind (midpoints). This approach has several advantages such as improved spectral selectivity and better time performance over the regular BEMD process. The MBEMD algorithm is then applied to the task of the interferometric fringe pattern analysis, to identify its distinct components. This allows to separate the oscillatory pattern component, which is of interest, from the background, noise and possibly other spurious interferometric patterns. In result, the phase demodulation error is reduced. Flexibility of the adaptive method allows for processing correlation fringe patterns met in the digital speckle pattern interferometry as well as the regular interferometric fringe patterns without any special tuning of the algorithm.

Flow control on a circular cylinder using streamwise-oriented Dielectric Barrier Discharge (DBD) plasma actuators was examined. These actuators generated pairs of counter-rotating streamwise vortices that influence overall flow characteristics. Particle Image Velocimetry (PIV) and aerodynamic force measurements were performed to analyze the flow control effectiveness. PIV measurements show that a streamwise-oriented DBD plasma actuator produced good suppression of flow separation at ReD = 3300 and the actuation effect was still discernible at higher ReD = 6530. However, this remarkable result was limited to region directly downstream of the exposed electrode where a downwash was present. Subsequent force measurements reveal a rise in both lift and drag acting on the cylinder when DBD plasma actuation was implemented. A maximum increase in lift coefficient ∆CL and drag coefficient ∆CD of 0.04 and 0.16 (+16%) were recorded, respectively. Surface pressure distributions estimated from PIV measurements indicate a pressure drop on the downstream-facing surface of the cylinder. The increase in streamwise pressure differential across the cylinder signifies a rise in drag acting on the cylinder.

The effect of active flow control on local flow separation behind the installation location of an ultra-high-bypass-ratio nacelle is investigated in a real-scale experiment at the TsAGI T-101 wind tunnel. The investigated model represents a swept 2.5D section of the pylon-wing junction in landing configuration. A flow control system employing periodic excitation is integrated into the unprotected leading edge inboard of the pylon. Tuft visualization as well as pressure and force measurements are used to investigate the vortex-dominated base flow and the effect of active flow control. It is shown that the flow control effect is governed by the normalized parameters of flow control, the momentum coefficient, and the velocity ratio, and is largely independent of the free-stream Mach and Reynolds number within the investigated range. The influence of a variation of the momentum coefficient on the lift gain is investigated. At the highest Reynolds number of an application of active flow control with fully eliminates local separation and increases total lift by approximately 2% of the respective baseline value across a range of 5 deg in angle of attack.

Closed-loop control of fluid–structure interactions on a flexibly supported cylinder

Health prediction of lithium-ion batteries by combining with empirical mode decomposition and PF-GPR algorithm

To overcome the convective time delay issue for active closed-loop flow control, a model based predictive control algorithm is analyzed. From a controls perspective, forms of internal model control or model predictive control can be used to accommodate and minimize the effect of systems with pure time delays. Moreover, the Smith predictor is a commonly employed control technique to negate the pure time delay in a closed-loop system. This form of model predictive control is applied to the asymmetric vortex problem of an axisymmetric forebody (specifically a von Karman ogive with fineness ratio of 3.5). The full-order Navier-Stokes equations are numerically solved on the forebody at a high angle of attack and provide the plant process. Small port and starboard blowing patches are used to introduce fluidic disturbances at the nose of the ogive to augment the global flow state and produce a deterministic vortex state. As the active flow control technique exploits a convective instability, a convective time delay exists. Linear-time-invariant and non-linear time-invariant models are developed from the open-loop dynamics. A Smith predictor is employed within the full order CFD simulation. The results of the predictive control are compared to open-loop and model-free closed-loop behavior. It is shown that the predictive control developed in this paper while very suitable for control of this type of flow, is very sensitive to modeling uncertainties.

Due to the ocean observation and detection requirements, as well as the construction of ocean defense system engineering, collecting and transmitting a large number of acoustic signals are prerequisite for subsequent processing and analysis. Massive detection data bring a big challenge for transmission lines and underwater processors. The detection acoustic signals can be compressed for storage and reconstructed for processing. In this paper, data compression methods are proposed based on wavelet transform and compressed sensing, the two algorithms are applied and compared for acoustic signal compression. The empirical mode decomposition algorithm is applied for pro-processing. Multilayer wavelet compression is used for getting a compressed acoustic signals. Gradient projection is used for sparse reconstruction. The experimental results show that both methods can perform well in acoustic signal compression, retain the main characteristics of the original acoustic signal, and greatly reduce signals to be transmitted and processed. Wavelet compression is faster in calculation. Compressed sensing is able to achieve a higher compression ratio.

In order to accomplish rapid detection of the damage in mooring steel strand of the offshore platform this paper proposes to use the ultrasonic guided wave method for the online damage detection. Considering the non-stationary characteristics of the ultrasonic signal, this paper proposes an Empirical Mode Decomposition} (EMD)-based algorithm to detect and localize the position of steel strand damage. To be specific, the detect signal is firstly decomposed by EMD into multiple Intrinsic Mode Functions (IMFs). Then, in order to find the weak damage signal which is usually buried in noise, a weighted synthesis procedure is adopted, i.e., assigning more weights to the dominant components of IMFs. By doing so, the reconstruction signal is denoised and the damage signal can be much more easily captured. Simulation results show that the proposed method can effectively detect the ultrasonic guided wave signal and realize the accurate localization of the weak damage to the steel strand by comparing with the traditional method of directly selecting several natural IMFs.

Hilbert–Huang transform analysis of storm waves

The performance of interpolation algorithm used in bi-dimensional empirical mode decomposition directly affects its popularization and application. Therefore, the research on interpolation algorithm is more reasonable, accurate and fast. So far, in the interpolation algorithm adopted by the bi-dimensional empirical mode decomposition, an adaptive interpolation algorithm can be proposed according to the image characteristics. In view of this, this paper proposes an image interpolation algorithm based on the particle swarm and fractal. Its procedure includes: to analyze the given image by using the fractal brown function, to pick up the feature quantity from the image, and then to operate the adaptive image interpolation in terms of the obtained feature quantity. The parameters involved in the interpolation process are optimized by particle swarm optimization algorithm, and the optimal parameters are obtained, which can solve the problem of low efficiency and low precision of interpolation algorithm used in bi-dimensional empirical mode decomposition. It solves the problem that the image cannot be decomposed to obtain accurate and reliable bi-dimensional intrinsic modal function, and realize the fast decomposition of the image. It lays the foundation for the further popularization and application of the bi-dimensional empirical mode decomposition algorithm.