Counterclockwise Vortex Research Articles

Periodic morphing of a NACA6409 aerofoil in ground effect, its wake mechanisms and thrust generation

Abstract The camber morphing of an aerofoil in ground effect was investigated using the FishBAC method and Detached Eddy Simulations with the k-omega SST turbulence model at a Reynolds number of 320,000. The aerofoil was periodically morphed at a start location of 25% chord from the leading edge with a trailing edge deflection range of 0.1% to 3% and morphing frequencies between a Strouhal number of 0.45 to 4 at a constant ground clearance of 10%. Periodically morphing the aerofoil using a sinusoidal function showed that lift and drag increased on the downstroke and decreased on the upstroke in the cycle, resulting in periodic values of lift and drag throughout the cycle. The amplitude of lift and drag increased as the morphing frequency and/or trailing edge deflection increased. It was found that the wake characteristics varied as a function of trailing edge deflection and morphing frequency. For small trailing edge deflections below 0.4% and frequencies below a 2.2 Strouhal number, Kelvin Helmholtz shedding was observed, and above this the wake became chaotic. Large trailing edge deflections showed Von-Karman shedding, where the interaction between the lower counter-clockwise vortex and the ground plane resulted in a jet-like flow that caused forward thrust. For the maximum deflection and morphing frequency tested in this study, reversed Von-Karman shedding was observed, which caused forward thrust from the interaction of the two-shedding counter-rotating vortices. Von-Karman or reversed Von-Karman shedding shows positive thrust generation, however, chaotic shedding should be avoided due to large drag gains. Varying the Reynolds number caused the Strouhal number to change as they depend on the same variables. It was found that the Strouhal number variation had a large effect on the wake, however, the Reynolds number had a minimal effect.

Heat transfer research on the cooling process of waxy crude oil storage in the vault tank based on VOF model

This paper focuses on the static cooling process for waxy crude oil stored in dome roof tanks. For the three phases of gas on top, liquid crude oil, and bottom water in storage tank, the VOF method is used to describe the evolution of physical quantities at the “oil–water”/“oil–gas” interface. The porous medium method is used to quantitatively characterize the sol–gel conversion process for waxy crude oil. A physical and mathematical models are established to describe the flow-heat transfer coupling behavior of the three-phase medium of crude oil, gas on top, and water at the bottom of the dome roof tank. In terms of the overall cooling process,The gas at the top of the tank has the simplest and fastest physical field evolution. It has the most uneven distribution (average temperature variance of 4 °C2), the strongest flow (average flow velocity of 0.4 m/s), the highest cooling rate (0.632 °C/h), and the lowest temperature (14.84 °C at the end). Its physical field is influenced by both the atmosphere and crude oil. The evolution of the physical field of crude oil is the most complex. It lags behind the gas at the top of tank and is directly effectted by it. Based on the evolution characteristics of the flow field of crude oil, the cooling process is divided into three stages: Stage I (0–––10 h) is the stage of convection generation and evolution in the crude oil region; Stage II (10 h − 34 h) is the stage of convection stability in the crude oil region; Stage III (after 35 h) is the stage of flow field transformation of crude oil. In stages I and II, the flow and momentum exchange at the oil–gas interface are significant. Crude oil is jointly influenced by the natural convection of the gas at the top of the tank and its own natural convection, forming a counterclockwise large vortex structure. The low-temperature area is near the central axis boundary of storage tank, oil–gas interface, and tank wall. The high-temperature area is within a range of 0.1 m − 3.3 m from the tank wall. After entering stage III, the flow and momentum exchange at the oil–gas interface weaken. The flow field of crude oil is only controlled by its own natural convection and transforms into a clockwise large vortex dominated. The low-temperature area is concentrated in the enclosed area of “oil–gas interface − tank wall” and “oil–water interface − tank wall”. The temperature field changes accordingly. Eventually, the high-temperature area is concentrated in the area slightly above the center of the tank. The physical field evolution of bottom water lags behind crude oil and is most unstable. Its cooling rate is 0.164 °C/h, slightly higher than crude oil’s 0.157 °C/h. The temperature is always slightly lower (33.47 °C at the end), and the physical field is the most uniform (average temperature variance of 0.0003 °C2), affected by the tank bottom environment and liquid crude oil.

A numerical study on the issue of Reynolds independence of flow and dispersion within isolated street canyons

Achieving Reynolds number independence is a prerequisite for conducting scale model experiments. This paper presents a numerical model of the two-dimensional isolated street canyon, utilizing the validated reliable k-epsilon turbulence model based on wind tunnel experimental data, to investigate the influence of approaching wind profiles (α) and windward building width (WB) on achieving Reynolds number independence in the isolated street canyon and compare these characteristics with those observed in urban street canyon. quantitative criteria, including revised relative change ratios (RRCs) ≤ 20% and dimensionless concentration relative difference (K_RD) ≤ 5%, were employed in conjunction with velocity, concentration contours, and streamlines to determine the corresponding critical Reynolds numbers. The results suggest that variations in approaching wind profiles primarily influence the flow field structure within the isolated street canyon after achieving Reynolds number independence, particularly impacting the scale of the counterclockwise vortex. However, these variations do not significantly alter the critical Reynolds number (Recrit) required for achieving Re-independence, which is estimated to be Recrit = 2.2×10⁴ for the isolated street canyon. Varying WB affects the formation of counterclockwise vortex within the isolated street canyon. A reduction in WB facilitates its formation and accelerates reaching Re-independence. The Recrit is found to be linearly proportional to WB variation. The flow field structure in urban street canyons remains relatively stable, with a recommended Recrit = 3.1×10⁴. When WB is 18 cm, the Recrit for the isolated street canyon aligns with that of the urban street canyon.

Vortex-shedding modes of a streamwise and transversely rotating sphere undergoing vortex-induced vibrations

We investigate the vortex-shedding modes of a streamwise and transversely rotating sphere undergoing vortex-induced vibration (VIV). At Reynolds number Re = 500, we have conducted direct numerical simulations for reduced velocities U∗=6,8, and 11, considering dimensionless streamwise (αx) and transverse (αz) rotation rates set at αx,z=1. At αx=1, the vortex-shedding mode exhibits twisted spiral-like structures, while at αz=1, ring-like structures form through the stretching and twisting of hairpins. For αx=1, the dimensionless circulation (Γx) decreases with increasing U∗, showing negative growth at U∗=6. Conversely, for αz=1, Γx remains negative except at U∗=8, where counterclockwise vortex rotation results in positive circulation. At αz=1, VIV is periodic for U∗=6 and 8 but intermittent at U∗=11. Phase analysis using the Hilbert transform reveals anti-phase synchronization in the phase between the sphere's displacements and the vortex force coefficient (ΔϕV) and phase slip in the phase between the sphere's displacements and the total force coefficient (ΔϕT) along the y direction for αx=1. At αz=1, phase slip with distinct phase-locking epochs is observed along the z direction for all U∗ cases. Pre-lock-in behavior with phase slip is also noted for U∗=11 along the y direction.

Large eddy simulation of wind turbulence over non-breaking and breaking waves

Wind-wave interaction affects the wind-wave fields and the combined loading on structures. This study aims to characterize turbulent airflow over non-breaking and breaking waves using a high-fidelity two-phase model in OpenFOAM. The volume of fluid method is utilized to model the complex air–water interface. Wind turbulence is considered via prescribing it at the inlet boundary. The model is validated against experimental data, and a numerical case study is conducted to simulate extreme wind and wave-plunging conditions. Results reveal that non-breaking waves induce wind turbulence and affect averaged wind velocity. For wave steepness exceeding 0.35, extreme wind forces amplify the turbulence by over 100% at wave crests. The amplified turbulence region extends to about 0.6λ in height. When waves plunge, an overturning jet propels the wind forward, generates a counterclockwise vortex, and enhances wind turbulence. Averaged wind speeds increase by over 20% above wave crests, with the enhanced region extending to a height of around 0.2λ for old waves. Maximum turbulence kinetic energy transiently increases by around 0.1Cp2 and maximum kinematic energy of wave-coherent velocity increases and subsequently decreases during wave plunging.

Experimental investigation of propagation evolution characteristics of internal solitary waves passing through downslope topography

In contrast to the extensive research on the propagation evolution of internal solitary waves (ISWs) over continental shelf topography, few investigations have been conducted on the propagation evolution of ISWs over downslope topography. In this experiment, the characteristics of the ISWs passing over a downslope topography were investigated in an immiscible two-layer fluid system to clearly capture the waveform information. The main objective of this study was to analyze the propagation evolution of ISWs with different incident amplitudes passing through a downslope topography. Using the particle image velocimetry technique, the evolutionary characteristics of ISWs (such as waveform, wave height, energy budget, and flow field) are investigated. According to the flow field analysis results, the phase velocity near the downslope topography changes with the propagation of ISWs. Moreover, the gradient distribution of velocity progressively becomes perpendicular to the right surface of the topography. Furthermore, a counterclockwise vortex gradually forms at the right upper vertex of the topography. The propagation of ISWs is influenced by varying water depth and topography. The front waveform of ISWs is significantly flat, and the back is steeper than the original back waveform. Around the tail wave, an upward convex wave packet is generated. The trends of wave energy and wave height losses are broadly consistent. Furthermore, the energy loss is related to the incident wave height with a 20% higher loss rate for large-amplitude ISWs than small-amplitude ISWs at the inflection point of the topography.

Effects of smoke on marine low clouds and radiation during 2020 western United States wildfires

Biomass burning aerosols (BBAs) influence the climate directly by scattering and absorbing sunlight and indirectly by changing the cloud properties through serving as cloud condensation nuclei (CCN) or ice-nucleating particles (INPs). Here we used the WRF-Chem model to simulate the transport of BBAs and their interactions with clouds and radiation during the western United States wildfires in September 2020. The simulated cloud and aerosol fields are comparable to the satellite observations from CALIPSO and MODIS. It is shown that smoke exerts negative radiative effects over both ocean and land. Over the nearly cloudless land, the negative radiative effect is caused by aerosols reflecting shortwave radiation. However, over the ocean covered by stratocumulus, aerosol-cloud interaction (ACI) induces a significant negative radiative effect (−25.6 W/m2 on average), because the reduction of droplet radius not only increases the brightness of clouds and prolongs their lifespan, but also cools their surroundings and increases relative humidity, which in turn increases cloud water content. On the contrary, aerosol-radiation interaction (ARI) leads to a positive radiative effect (+10.3 W/m2 on average) over the oceanic regions due to the absorption of sunlight reflected by low clouds and a slight decrease in cloud water. In our research, the counterclockwise vortex over the Northeast Pacific transports the smoke to remote regions and lifts the smoke to 4–8 km height. This results in a wide-ranging impact of the smoke on clouds and radiation, yet it diminishes the magnitude of ARI's effect on marine stratocumulus. Moreover, over ocean, ARI results in cooling at the cloud top and warming close to the sea surface, leading to a rise in marine stratocumulus height. These vertical atmospheric adjustments within the PBL differ from the reduced surface temperature with suppressed PBL over terrestrial regions.

STUDY OF CARDIAC FLUID DYNAMICS IN THE RIGHT SIDE OF THE HEART WITH AI PIV

Particle image velocimetry (PIV), when used to investigate cardiac flows, has been restricted to the exploration of left-heart hemodynamics. Easy phantom modeling, simple geometrical assumptions, and the use of modified ultrahigh-frequency 3-D echocardiographic probes dedicated to the left heart are the main reasons for this restriction. However, hemodynamics of the right heart, due to its complex geometry, is still poorly understood. AI PIV, based on deep learning and convolutional neural networks, offers a super-resolution view of the velocity fields. In this paper, we apply this new technique to agitated saline bubble echocardiographic recordings of the right heart. The obtained higher-resolution results show promising patterns and vortices throughout the cardiac cycle, circumventing the abovementioned obstacles. For instance, the annular tricuspid excursion, which has been used for decades as a marker of systolic function of the right ventricle, seems to be crucial for the formation of two diastolic vortices in the right atrium. A lateral counterclockwise vortex and a medial clockwise vortex that direct flow from the low-pressure right atrium to the middle of the tricuspid valve were noted repeatedly throughout different cardiac cycles within the same patients and between different patients.

Effects of gas flow rate on rising bubble chains and induced flow fields: An experimental study

This paper reports an experimental investigation of the characteristics of bubble chains and their induced flow fields in a quiescent fluid at gas flow rates of 5, 10, 50, and 100 ml/min. The shadowgraphy and laser-induced-fluorescence particle image velocimetry (LIF-PIV) were used to analyze quantitatively the bubble morphology, kinematics, and induced flow fields. The results show that with increasing gas flow rate, the bubbles exhibit a larger average diameter, aspect ratio, and more-abundant morphology. The bubble motion includes a rectilinear rise followed by an oscillating rise, and the position where the bubble deviates from the linear trajectory is associated with the point of maximum bubble aspect ratio. The amplitude of bubble oscillation and the position of the instability both increase with the gas flow rate, except for the case of 50 ml/min. The bubble-induced flow field at higher gas flow rates exhibits stronger entrainment, which reflects the ability of the flow to entrain the surrounding fluid. The instantaneous flow-field results show that bubble-induced wake shedding is the main cause of the change in bubble rise state and trajectory instability. The direction of bubble deflection is related directly to the sequence of wake shedding: when the clockwise (resp. counterclockwise) vortex in the wake is the first to shed, the bubble deflects to the left (resp. right). The study also reveals that the simultaneous shedding of counterclockwise and clockwise vortices at 50 ml/min results in the bubbles continuing to rise rectilinearly for a period of time, and the position of trajectory destabilization has a maximum height.

Machine learning-based optimization of a pitching airfoil performance in dynamic stall conditions using a suction controller

Flow separation control on oscillating airfoils is crucial for enhancing the efficiency of turbine blades. In this study, a genetic algorithm was employed to optimize the configuration of a pure suction jet actuator on an oscillating airfoil at a Reynolds number of 1.35×105. Neural networks based on multilayer perceptrons were used to train the aerodynamic coefficients as functions of the control parameters and reduce the number of simulations. The objective function was the mean performance coefficient, defined as the ratio of the average lift to the average drag during an oscillation period. The control parameters were location, velocity, opening length, and suction jet angle relative to the airfoil surface. The optimal jet had the maximum velocity and opening length and was normal to the airfoil surface. The optimal jet location was near the leading edge vortex (LEV) (between 3% and 6% of the chord). The optimum jet can increase the average performance coefficient (average ratio of lift to drag during a period) by about 24 times. The major part of this improvement is related to reducing drag force. The average lift coefficient increases from about 0.58 to about 0.92 using this jet, while the average drag coefficient decreases from about 0.23 to about 0.02. The optimal jet suppressed the dynamic stall vortex, which resulted from the combination of two clockwise vortices: LEV and turbulent separation vortex. Suppressing this vortex prevented the counterclockwise trailing edge vortex from growing at the end of the airfoil.

Numerical study on particle distribution characteristics of slush hydrogen in a cryogenic tank

A numerical model considering phase change and heat transfer was established by the Euler-Euler two-fluid method to investigate the storage characteristics and two-phase flow field of slush hydrogen. Numerous numerical simulations were performed to discuss the effect of particle diameter (dp = 0.02–0.5 mm), content of solid hydrogen (αs = 10%–50%), and heat leakage (q = 50–200W·m−2) on the flow field. It was found that particle deposition could occur during the storage process, and there exist moving vortices with contrary directions under specific conditions. The sedimentation characteristics and vortex size are influenced by many factors including particle size, solid hydrogen content, and heat leakage. An increase in particle size could lead to the strengthening of precipitation and the expansion of the counterclockwise vortex region on the right side of the tank. And the increase in solid hydrogen content could result in more deposition and more collisions and friction between particles. Moreover, the increase in heat leakage could increase the area of the counterclockwise vortex. Numerical results of the deposition and flow field characteristics in the storage tank could clearly show the physical law of the slush hydrogen so that the uniform distribution of slush hydrogen could be promoted for efficient storage and application.

Modulational Instability and Spectral Broadening of Vortex Modes in Chiral Photonic Crystal Fibers

We report on intra- and inter-modal four-wave-mixing (FWM) in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> -fold rotationally symmetric (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</sub> ) single- and multi-core chiral photonic crystal fiber (PCF), created by spinning the preform during fiber drawing. The non-circular modal field is forced to rotate as it propagates along the fiber, resulting in circular birefringence and robust maintenance of circular polarization state. Multi-core chiral C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</sub> PCF supports vortex-carrying helical Bloch modes (HBMs) in which the degeneracy between clockwise and counter-clockwise vortices is lifted. This makes possible new kinds of intermodal polarization modulational instability (PMI). We develop PMI theory for vortex HBMs, and illustrate the results by a series of experiments in which two or more PMI sidebands with different vorticities and polarization states are selectively generated by adjusting the polarization state and topological charge of the pump light. In every case both the topological charge and the spin of the pump light are conserved. We also report generation of a broadband supercontinuum in a single circularly polarized vortex mode.

Surface flow and aerodynamic drag of Ahmed body with deflectors

This study investigated the surface flow and the aerodynamic characteristics of a 7/10 scale Ahmed model equipped with deflectors at several angles. The experiments were conducted at Reynolds number of 2.45 × 105 based on the model height. A global luminescent oil film skin-friction measurement technique was applied for the flow fields on the slant and base surfaces. The aerodynamic forces of the model were measured to understand the effect of the deflection angle on the aerodynamic characteristics. The pressure was measured and pressure drags acting on the slant and base surfaces were also calculated. The results showed that the drag and lift of the model suddenly dropped at the deflection angle above −5°. The pressure distribution on the slant and base surfaces became flat with a maximum drag reduction of 8% for the model with a deflection angle of 0°. The skin-friction measurement indicated that the drag reduction was connected to the breakdown of the separation bubble and longitudinal vortices on the slant. At the fully separated flow state, the skin-friction results illustrated two small vortices and a counter-clockwise vortex on the slant. Additionally, the wake vortices shifted from horizontal to vertical structures. The relation among the flow fields on the slant surface, flow on the symmetric plan, pressure distribution, and drag was illustrated for the model with different deflection angles.

Macroscopic Spiral Patterns of Cholesteric Cellulose Nanocrystals Induced by Chiral Doping and Vortex Flowing.

Negatively surface-charged sulfate cellulose nanocrystals (CNCs) are always slowly self-assembled into left-handed cholesteric mesophases. In this work, macroscopic spiral patterns induced by counterclockwise vortex flowing or chiral doping were investigated. Results show that iridescent patterns of the arithmetic spiral, rose spiral, or latitude ripples were generated under the vortex rotation, indicating a severe microphase separation of CNCs. Moreover, the spiral pattern and rotational symmetry were highly correlated to the twisting and flowability of CNCs as well as chiral dopants. Alternatively, the cholesteric pitch and maximum reflective wavelength (λmax) of CNCs were strongly increased by sinistral dopants other than the dextral ones, indicating an enhanced torsion of left-handed CNC mesophases by the dextral dopants. In addition, macroscopic spiral patterns distinctly existed in dextrally doped CNCs owing to a synergistic chiral enhancement. Therefore, the mechanochiral or chemical chiral transition from microscopic twisting to macroscopic spiral provides a potential inspiration for chiral self-organization of biological macromolecules.

Numerical study of vortex-induced autorotation of an elliptic blade in lid-driven cavity flow

Large-scale eddies in a lid-driven cavity are potential sources of angular momentum which can induce rotational effect in a free-to-rotate inertial body due to fluid–structure interaction. The novel objective of the present study is to investigate vortex-induced autorotation of an elliptic blade hinged at the centre of a lid-driven cavity. The governing equations are numerically solved using iterative direct forcing immersed boundary method. The impact of Reynolds number and blade length on dynamics characteristics of the blade are analysed. Considering left to right motion of horizontal top lid, four different vortex-induced modes are identified as the steady blade response, including stationary position, small-amplitude fluttering, clockwise autorotation and counter-clockwise autorotation. Long blades are mostly potential for steady clockwise autorotation, particularly in higher Reynolds numbers, due to dominance of principal near-wall cavity vortex compared to other vortices. In contrast, effective role of central counter-clockwise vortex in a short blade and weak interaction of such blade with the near-wall cavity vortex leads to a steady counter-clockwise rotation, particularly in high Reynolds numbers. In the case of low Reynolds numbers or blade with moderate length, vortex-induced blade motions in clockwise and counter-clockwise directions are fairly balanced, leading to stationary position or small-amplitude fluttering modes.

Effects of Blade Suction Side Modification on Internal Flow Characteristics and Hydraulic Performance in a PIV Experimental Centrifugal Pump

In this paper, the effects of blade trailing edge (TE) profile modification of the suction side on the internal flow and hydraulic performance in a low-specific speed centrifugal pump are investigated through particle image velocimetry (PIV) analysis. Three impellers with different blade trailing edge profiles named original trailing edge (OTE), arc trailing edge 1 (ATE1), and arc trailing edge 2 (ATE2) are designed for PIV experiments. Results show that blade trailing edge modification of the suction side can significantly change the flow pattern, affecting the hydraulic performance of the model pumps. There is a definite counterclockwise backflow vortex near the suction side of OTE at deep-low flow rate, resulting in a decrease in the uniformity of the flow field at the outlet and the hydraulic performance. ATE1 with a reasonable larger blade outlet angle has the best flow field, and the head and efficiency are increased by about 1.2% and 8%, respectively under the same working condition. The hydraulic performance of ATE2 with the blade outlet angle of 59° is better than that of OTE under low flow rate, but it is less than that of OTE under high flow rate due to the streamline deviation generated on the pressure side. Meanwhile, the energy conversion abilities of the modified model pumps are evaluated by slip factor and the deviation degree of the nominalized local Euler head distribution (NLEHD). Since there is no definite counterclockwise backflow vortex at the outlet after modification, the slip factor of ATEs increases and the energy conversion ability is enhanced. Moreover, the jet-wake phenomenon of ATEs is weakened, and the local Euler head (LEH) increases near the outlet, decreasing the deviation degree of the NLEHD to obtain better energy conversion ability.

Accurate Background Reduction in Adaptive Optical Three-Dimensional Stimulated Emission Depletion Nanoscopy by Dynamic Phase Switching

Stimulated emission depletion (STED) fluorescence nanoscopy allows the three-dimensional (3D) visualization of nanoscale subcellular structures, providing unique insights into their spatial organization. However, 3D-STED imaging and quantification of dense features are obstructed by the low signal-to-background ratio (SBR) resulting from optical aberrations and out-of-focus background. Here, combining adaptive optics elements, we present an easy-to-implement, flexible, and effective method to improve the SBR by dynamic phase switching. By switching to a counterclockwise vortex phase mask and a top-hat one with an incorrect inner radius, the depletion pattern features a nonzero-intensity center, enabling accurate background recordings. When the recorded background is subtracted from the aberration-corrected 3D-STED image, the SBR in dense sample areas can be improved by a factor of 3–7 times. We demonstrate our method on various dense subcellular structures, showing more advantages than the software-based background subtraction algorithms.

Interaction of quasi-two-dimensional vortical gusts with airfoils, unswept and swept wings

A nearly two-dimensional vortex of small core size has been produced by the transient plunging motion of an upstream airfoil and it interacted with the downstream wings. Depending on the offset distance of the vortex and wing angle of attack, the incident vortex filament deforms, diffuses, and loses coherence, while inducing leading-edge vortex formation and shedding from the wing. No significant spanwise flow develops in the incident vortices during the interaction. The interaction with the swept wing at each spanwise plane appears to be unaffected by the other spanwise planes. The counter-clockwise vortex induces a positive lift peak as it approaches the wing, which can be predicted by the potential flow assumption. The peak lift force is proportional to the circulation of the incident vortex and has its maximum near the zero-offset distance. The minimum lift coefficient is reached after the vortex has just passed and caused flow separation on the lower surface. The maximum lift coefficients for the finite unswept and swept wings can be estimated by making a correction for the aspect ratio and using the independence principle. The only exception is observed for the swept wing at a post-stall angle of attack for which the leading-edge vortex shedding becomes parallel to the leading-edge and increases the peak lift force.Graphical abstract

Plasma actuator effects on the flow physics of dynamic stall for a vertical axis wind turbine

Darrieus type vertical axis wind turbines have several advantages over other wind turbines for local electricity generation in urban environments. However, the main aerodynamic challenge is the negative impacts of the dynamic stall phenomenon on the turbine performance. This study numerically scrutinizes the effects of plasma actuators on the dynamic stall control and performance improvement of a Darrieus turbine. For this sake, unsteady Reynolds-averaged Navier–Stokes equations are solved using a pressure-based finite volume method. The Suzen–Hoang plasma actuator model is employed to calculate the body forces attributed to the plasma actuator. First, the dynamic stall characteristics of the turbine blade with no plasma actuator are explored. Then, three plasma actuator configurations (i.e., inboard, outboard, and double-sided) are considered. According to the results of the clean blade, the aerodynamic performance mainly depends on the reverse Karman vortex formation at the onset of the down-stroke motion and counterclockwise vortex formation on the blade suction side. The results of plasma configurations indicate that the inboard and double-sided actuators enhance the turbine power output by 10%, while the outboard actuator effects are negligible. Moreover, the plasma actuator is effective only in the down-stroke motion of the blade. Results also show that the inboard and double-sided plasma actuators eliminate the reverse Karman vortex and significantly reduce the counterclockwise vortex size, increasing the lift force and connection point moment. Consequently, the inboard and double-sided plasma actuators remove the negative torque generation in azimuth angles of 135° to 180°, primarily responsible for the output power enhancement.

3D Acoustic Manipulation of Living Cells and Organisms Based On 2D Array.

Flexible manipulation techniques for living cells and organisms are extremely useful tools for fundamental biomedical and life science research. Acoustic tweezers, which permit non-contact, label-free manipulation, are particularly suited to micromanipulation tasks as they provide a large acoustic radiation force and can be applied in various media. Here, we describe the design and fabrication of a 3 MHz, 64-element (8 × 8), 2D planar ultrasound array that realizes the multidimensional translation, rotation, orientation, and levitation of living cells and organisms. The focusing vortex and twin fields are generated using the holographic acoustic elements framework method. We demonstrate that the eggs and larvae of brine shrimp can be translated along a preset trajectory by controlling the central position of the vortex. By multiplexing counterclockwise vortices, clockwise vortices, and twin trap fields in a time sequence, the rotation direction of the shrimp eggs can be switched in real time, while non-spherical larvae can be reoriented. Moreover, the reflection of the acoustic beam can lift eggs and larvae from the bottom of the culture dish and further manipulate them in the vertical and horizontal directions. Additionally, we present quantitative analyses of the shrimp-egg rotation frequency with respect to the focal depths, topological charges of the vortex, and excitation voltages. These results indicate that acoustic tweezers based on 2D matrix arrays can realize complex and selective manipulation of living cells and organisms, thereby demonstrating their value for advancing research in the fields of cell assembly, tissue engineering, and micro-robot driving.