Actuators are transducers that convert an electrical signal to a desired physical quantity. Active flow control actuators modify by providing electronically controllable disturbance. The field of active has witnessed explosive growth in the variety actuators, which is testament both importance and challenges associated with actuator design. This review provides framework for discussion specifications, characteristics, selection, design, classification aeronautical applications. Actuator...

Af ormation criterion for synthetic jets is proposed and validated. A jet actuator a zero-net mass-flux device that imparts momentum to its surroundings. Je tf defined as the appearance of time-averaged outward velocity along axis corresponds generation subsequent convection or escape vortex ring. It shown over wide range operating conditions formation governed by Strouhal number Sr (or Reynolds Re Stokes S). Both numerical simulations experiments are performed supplement available...

Abstract : This paper presents a lumped element model of piezoelectric-driven synthetic jet actuator. A jet, also known as zero net mass-flux device, uses vibrating diaphragm to generate an oscillatory flow through small orifice or slot. In modeling (LEM), the individual components are modeled elements equivalent electrical circuit using conjugate power variables. The frequency response function is derived obtain expression for Q(sub out)/V(sub AC), volume rate per applied voltage. analyzed...

This paper presents the development of a micromachined acoustic energy harvester for aeroacoustic applications. The employs silicon-micromachined circular, piezoelectric composite diaphragm electroacoustic transduction. Lumped element modeling, design, fabrication and characterization prototype are presented. Experimental results indicate maximum output power density 0.34 µW cm−2 at 149 dB (ref. 20 µPa) suggest potential density, this 250 with an improved process.

Multiple distinct peaks of comparable strength in unsteady pressure autospectra often characterize compressible flow-induced cavity oscillations. It is unclear whether these different large-amplitude tones (i.e., Rossiter modes) coexist or are the result a mode-switching phenomenon. The cause additional spectrum, particularly at low frequency, also unknown. This article describes analyses data using time-frequency methods, namely short-time Fourier transform (STFT) and continuous Morlet...

Using microphone arrays for estimating source locations and strengths has become common practice in aeroacoustic applications. The classical delay-and-sum approach suffers from low resolution high sidelobes the resulting beamforming maps are difficult to interpret. deconvolution mapping of acoustic sources (DAMAS) algorithm recovers actual levels contaminated results by defining an inverse problem that can be represented as a linear system equations. In this paper, is carried onto sparse...

This paper presents the development of an acoustic energy harvester using electromechanical Helmholtz resonator (EMHR). The EMHR consists orifice, cavity, and a piezoelectric diaphragm. Acoustic is converted to mechanical when sound incident on orifice generates oscillatory pressure in which turns causes vibration conversion electrical achieved via transduction diaphragm EMHR. Moreover, coupled with reclamation circuitry increase efficiency conversion. Lumped element modeling used provide...

Dynamic mode decomposition (DMD) is a popular technique for modal decomposition, flow analysis, and reduced-order modeling. In situations where system time varying, one would like to update the system's description online as evolves. This work provides an efficient method computing DMD in real time, updating approximation of dynamics new data becomes available. The algorithm does not require storage past computes exact matrix using rank-1 updates. A weighting factor that places less weight...

Flow-induced cavity resonance is characterized by large amplitude tones in and around the cavity. While passive suppression techniques can be optimized for a single operating condition, their performance often degrades at offdesign conditions. Active control attractive because of its potential to adapt different conditions without significant degradation. This paper describes an investigation active flow-induced low Mach numbers. Attention focused on deep (Z/D=0.5) shallow (L/D=2.0). For...

This paper presents an analytical two-port, lumped-element model of a piezoelectric composite circular plate. In particular, the individual components unimorph transducer are modeled as lumped elements equivalent electrical circuit using conjugate power variables. The transverse static deflection field function pressure and voltage loading is determined to synthesize two-port dynamic model. Classical laminated plate theory used derive equations equilibrium for clamped plates containing one...

This paper describes the design, fabrication, and characterization of a bulk-micromachined piezoelectric microphone for aeroacoustic applications. Microphone design was accomplished through combination composite plate theory lumped element modeling. The device consists 1.80-mm-diam, 3-μm-thick, silicon diaphragm with 267-nm-thick ring material placed near boundary to maximize sensitivity. fabricated by combining sol-gel lead zirconate-titanate deposition process on silicon-on-insulator wafer...

Zero-net mass-flux jet based control of flow separation over a stalled airfoil is examined using numerical simulations. Two-dimensional simulations are carried out for NACA 4418 at chord Reynolds number 40,000 and angle attack 18 deg. Results the uncontrolled indicate presence three distinct natural time scales in corresponding to shear layer, bubble, wake regions. The frequencies used select appropriate forcing frequencies, it found that closer bubble frequency elicit best response terms...

The mechanism of trailing vortex wandering has long been debated and is often attributed to either wind-tunnel effects or an instability. Using particle image velocimetry data obtained in the wake a NACA0012 airfoil, we remove effect from measured velocity field and, through triple decomposition, recover coherent motion. Based on this motion, most energetic structures are computed using proper orthogonal decomposition (POD) exhibit helical mode with azimuthal wavenumber $|m|=1$ whose kinetic...

Recent advances in manufacturing techniques are providing porous media with both high permeability, necessary for effective passive flow control, and structural strength, essential engineering applications. We therefore examine the predictive accuracy of standard Darcy–Forchheimer (DF) law, which is often used to model flows, inclusion Reynolds numbers (Re) ranging from low linear regime nonlinear where unsteady effects such as vortex shedding become evident. consider two different shapes,...

In image-based measurements, quantitative image data must be mapped to three-dimensional object space. Analytical photogrammetric methods, which may used accomplish this task, are discussed from the viewpoint of experimental fluid dynamicists. The Direct Linear Transformation (DLT) for camera calibration, in pressure sensitive paint, is summarized. An optimization method calibration developed that can determine parameters, including those describing lens distortion, a single image. Combined...

This paper proposes and validates a jet formation criterion for synthetic actuators. The is zero net mass flux device, adding additional momentum but no to its surroundings. Jet defined as mean outward velocity along the axis corresponds clear of shed vortices. It shown that governed by Strouhal number (or Reynolds Stokes number). Numerical simulations experiments are performed supplement available two-dimensional axisymmetric data in literature. support , where constant 2 Re/ S K >...

The flow associated with a synthetic jet transitioning to turbulence in an otherwise quiescent external is examined using time-accurate three-dimensional numerical simulations. incompressible Navier–Stokes solver uses second-order accurate scheme for spatial discretization and semi-implicit fractional step method time integration. simulations are designed model the experiments of C. S. Yao et al . ( Proc. NASA LaRC Workshop , 2004) which have examined, detail, evolution transitional flow....

Microphone arrays are commonly used for noise source localization and power estimation in aeroacoustic measurements. The delay-and-sum (DAS) beamformer, which is the most widely beamforming algorithm practice, suffers from low resolution high sidelobe level problems. Therefore, deconvolution approaches, such as approach mapping of acoustic sources (DAMAS), often extracting actual powers contaminated DAS results. However, approaches assume that uncorrelated. Although algorithms can deal with...

High-lift devices often generate an unsteady flow field producing both broadband and tonal noise which radiates from the aircraft. In particular, leading edge slat is a dominant contributor to signature. An experimental study of simplified unswept high-lift configuration, 30P30N, has been conducted understand identify various flow-induced sources around slat. Closed-wall wind tunnel tests are performed in Florida State Aeroacoustic Tunnel (FSAT) characterize cove using combination surface...