Considering the number of applications, and the quantity of research conducted over the past few decades, it wouldn't 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, are covered. Along with this, investigations into different control algorithms, for the piezoelectric based active vibration control, are also reviewed. Studies reporting the use of piezoelectric modal filtering and self sensing actuators, for active vibration control, are also surveyed. Additionally, research on semi-active vibration control techniques like the synchronized switched damping (on elements like resistor, inductor, voltage source, negative capacitor) has also been covered

https://iopscience.iop.org/article/10.1088/1361-665X/ab7541/pdf

Review on the use of piezoelectric materials for active vibration, noise, and flow control

Progress in tribological research of SiC ceramics in unlubricated sliding-A review

Tribological characteristics of SiC ceramics sintered with a small amount of yttria

Effect of dielectric barrier discharge plasma actuator on the dynamic moment behavior of pitching airfoil at low Reynolds number

In this review, we summarize existing trends of flow control used to improve the aerodynamic efficiency of wings. We first discuss active methods to control turbulence, starting with flat-plate geometries and building towards the more complicated flow around wings. Then, we discuss active approaches to control separation, a crucial aspect towards achieving a high aerodynamic efficiency. Furthermore, we highlight methods relying on turbulence simulation, and discuss various levels of modeling. Finally, we thoroughly revise data-driven methods and their application to flow control, and focus on deep reinforcement learning (DRL). We conclude that this methodology has the potential to discover novel control strategies in complex turbulent flows of aerodynamic relevance.

https://www.mdpi.com/2311-5521/7/2/62/pdf?version=1644399108

Flow Control in Wings and Discovery of Novel Approaches via Deep Reinforcement Learning

In an effort to develop an understanding of the tribological properties of silicon carbide (SiC) in a cryogenic environment, this contribution reports on the results of the sliding wear properties of the self-mated SiC in liquid nitrogen (LN2). Two sets of sliding wear tests were conducted in a planned manner in LN2 under varying combinations of operating conditions, using a specially designed high-speed cryo-tribometer. In the first set, the sliding velocity is varied up to 1.1 m/s, for 600 s, at a constant load of 5 N; while the second set of experiments were conducted with loads of 5, 10, and 15 N, at a constant speed of 3.3 m/s for 900 s, thereby enabling to evaluate tribological potential over a broad spectrum of operating conditions. In our experiments, high coefficient of friction (COF) (0.28–0.40) and high wear resistance (∼10−7–10−6 mm3/N m) have been measured for self-mated SiC. The topographical observations using a scanning electron microscope reveal that limited tribochemical layer formation, as well as grain boundary microfracture-induced damage mechanisms, contribute to the wear of self-mated SiC. The experimental results are critically analyzed with reference to flash temperature and contact stress conditions, as well as compared with some baseline experiments, conducted under ambient conditions. A comparison with our earlier research results, obtained with self-mated Al2O3 or ZrO2, establishes the good tribological potential of self-mated SiC in LN2, in terms of exhibiting a better combination of COF and wear rate.

Microfracture and Limited Tribochemical Wear of Silicon Carbide During High‐Speed Sliding in Cryogenic Environment

Active flow control has the potential for substantial performance gains and meeting the challenges of next-generation air vehicles. High-lift airfoils employ trailing edge flaps during takeoff and ...

Active Flow Control of a High-Lift Supercritical Airfoil with Microjet Actuators

Vortex asymmetry develops on slender bodies at high angles of incidence, leading to large side-forces and yaw moments even in symmetrical flight conditions. In the present experimental study, the flow over a slender body consisting of a conical forebody and a cylindrical aftbody is studied at high angles of incidence at low speeds. Experiments consisted of force measurements using a six-component strain gauge balance and velocity field using Particle Image Velocimetry. Results show that a pair of counter-rotating vortices develop nearly symmetrically over a polished cone but become asymmetric over the cylinder. Several secondary shear-layer vortices develop at the cone–cylinder junction and over the cylinder due to sharp turning angle, surface imperfections, and joints. These secondary shear-layer vortices then merge with the primary vortex pair, leading to the flow asymmetry. The flow characteristics and side-forces vary significantly when the conical forebody is rotated about its axis of symmetry and set to different azimuthal positions. The results strongly suggest that a change in the geometry at the cone–cylinder junction and surface imperfections present on the cylindrical aftbody play an important role in determining the overall flow-asymmetry and the magnitude of side-forces generated on the slender body at high angles of incidence.

Role of secondary shear-layer vortices in the development of flow asymmetry on a cone–cylinder body at high angles of incidence

The present study primarily focuses on the design, development, and structural characterization of an oscillating winglet actuated using a piezoelectric macrofiber composite (MFC). The primary objective is to study the effect of controlled wingtip oscillations on the evolution of wingtip vortices, with a goal of weakening these potentially harmful tip vortices by introducing controlled instabilities through both spatial and temporal perturbations producible through winglet oscillations. MFC-actuated winglets have been characterized under different input excitation and pressure-loading conditions. The winglet oscillations show bimodal behavior for both structural and actuation modes of resonance. The oscillatory amplitude at these actuation modes increases linearly with the magnitude of excitation. During wind-tunnel tests, fluid-structure interactions led to structural vibrations of the wing. The effect of these vibrations on the overall winglet oscillations decreased when the strength of actuation increased. At high input excitation, the actuated winglet was capable of generating controlled oscillations. As a proof of concept, the current study has demonstrated that microfiber composite-actuated winglets produce sufficient displacements to alter the development of the wingtip vortex.

http://iopscience.iop.org/article/10.1088/0964-1726/24/6/065043/pdf

Characterization of piezoelectric macrofiber composite actuated winglets

Initial perturbations in the wingtip vortices can potentially lead to instabilities that significantly reduce their lifetime in the wake of an aircraft. An active winglet capable of oscillating about its point of attachment to the main wing-section is developed using piezoelectric macro fiber composite, to actively perturb the vortex at its onset. Resonance characteristics of the actuated winglet oscillations are evaluated at different excitation levels and aerodynamic loading. Mean near-field characteristics of the vortex, developing from a stationary and an oscillating winglet, are investigated with the help of stereoscopic particle image velocimetry. Results show that the amplitude of winglet oscillations increases linearly with input excitation, to a highest attainable value of nearly four times the airfoil thickness at the winglet tip. The vortex developing from a winglet is stretched along its axis, having an elliptical core with non-uniform vorticity distribution. Actuation leads to spatial oscillations of the vortex core together with a reduction in the mean peak vorticity levels. The amplitude of the actuated core oscillations remains constant in the investigated region of the wake.

Tufan Kumar Guha

Papers

Microfracture and Limited Tribochemical Wear of Silicon Carbide During High‐Speed Sliding in Cryogenic Environment

Active Flow Control of a High-Lift Supercritical Airfoil with Microjet Actuators

Role of secondary shear-layer vortices in the development of flow asymmetry on a cone–cylinder body at high angles of incidence

Characterization of piezoelectric macrofiber composite actuated winglets

Characteristics of a wingtip vortex from an oscillating winglet