Explore the vast range of titles available.

We investigate the influence of rotation on the onset and saturation of the Faraday instability in a vertically oscillating two-layer miscible fluid using a theoretical model and direct numerical simulations (DNS). Our analytical approach utilizes Floquet analysis to solve a set of the Mathieu equations obtained from the linear stability analysis. The solution of the Mathieu equations comprises stable and harmonic, and subharmonic unstable regions in a three-dimensional stability diagram. We find that the Coriolis force delays the onset of the subharmonic instability responsible for the growth of the mixing zone size at lower forcing amplitudes. However, at higher forcing amplitudes, the flow is energetic enough to mitigate the instability delaying effect of rotation, and the evolution of the mixing zone size is similar in both rotating and non-rotating environments. These results are corroborated by DNS at different Coriolis frequencies and forcing amplitudes. We also observe that for $(\\,f/\\omega )^2<0.25$, where $f$ is the Coriolis frequency, and $\\omega$ is the forcing frequency, the instability and the turbulent mixing zone size-$L$ saturates. When $(\\,f/\\omega )^2\\geq 0.25$, the turbulent mixing zone size-$L$ never saturates and continues to grow.

Rotating Rayleigh–Bénard convection denotes the convection between a warm plate and a cold plate in a rotating environment. It is a classic model for understanding convective vortices in the atmosphere and ocean. The influence of background rotation on fluid inertia breaks the symmetry between cyclones and anticyclones. Such a symmetry breaking could be represented by vorticity skewness, which still lacks a systematic theory. Rapidly rotating convection with stress-free boundaries and unit Prandtl number is a convenient starting point. The investigation starts from the convective onset stage, where the vortices grow stationarily. Asymptotic analysis shows that the volumetric vorticity skewness $S$ is produced by the interaction between the $n=0,1$ and $n=1,2$ vertical eigenmodes. The $n=0$ (barotropic) mode contributes positively to $S$ mainly by stretching the vertical relative vorticity, an ageostrophic effect. The $n=2$ mode makes a minor negative contribution to $S$ by preferentially intensifying the outflow over the inflow, a non-hydrostatic effect. The theory predicts $S$ to be proportional to the global Rossby number defined with the volumetric standard deviation of vorticity, ${Ro_g}$. The proportional factor does not depend on the Rayleigh and Ekman numbers, agreeing with direct numerical simulations. Then the system enters the equilibrium stage. The stretching of vertical vorticity still contributes to $S$ dominantly. At ${Ro_g}\\gtrsim 0.5$, the emergent unsteady flow significantly suppresses the asymmetry between the inflow and outflow strength, and weakens its influence on $S$.

Large-eddy simulations (LES) are employed to investigate the role of time-varying currents on the form drag and vortex dynamics of submerged 3D topography in a stratified rotating environment. The current is of the form U c + U t sin(2 πf t t ), where U c is the mean, U t is the tidal component, and f t is its frequency. A conical obstacle is considered in the regime of low Froude number. When tides are absent, eddies are shed at the natural shedding frequency f s , c . The relative frequency is varied in a parametric study, which reveals states of high time-averaged form drag coefficient. There is a twofold amplification of the form drag coefficient relative to the no-tide ( U t = 0) case when lies between 0.5 and 1. The spatial organization of the near-wake vortices in the high drag states is different from a Kármán vortex street. For instance, the vortex shedding from the obstacle is symmetric when and strongly asymmetric when . The increase in form drag with increasing stems from bottom intensification of the pressure in the obstacle lee which we link to changes in flow separation and near-wake vortices.

We present an autonomous add-on measurement system for detailed aerodynamic measurements on full scale turbines. From the measured data we can derive the local aerodynamic coefficients for the blade section and e.g. compare with wind tunnel data for a similar section. This forms the basis for evaluating how well the airfoil performs on a rotor in the turbulent inflow and rotating environment. We describe the measurement system which comprises a pressure belt with 15 taps, a flyboard with the data acquisition system and a five hole pitot tube measuring the local inflow to the blade section. The system was used on a SWT-4.3-120 DD turbine in a short campaign in June 2021. A trailing edge flap system is installed on that turbine and a particular objective with the measurements was to evaluate the static and dynamic performance of the flap system. The aerodynamic measurements were correlated with the SCADA and flap actuation data. Overall the measurement system performed well and provided good data like smooth pressure distributions. The derived flap performance in the form of the delta lift coefficient was close to what has been measured in wind tunnel tests. Finally, the aerodynamic and aeroelastic dynamic time response of the flap actuation could be characterized with good precision.

Small-mouth Kelvin number plumes, or plumes with a source width smaller than the deformation radius, are characterized by near-field plume regions of rapid lateral expansion and strong vertical mixing. Net plume mixing, or the dilution of a plume by ocean water between the estuary mouth and the far-field plume, is examined using idealized numerical experiments with the Regional Ocean Modeling System (ROMS). The density anomaly of plume water entering the far field is determined from isohaline analysis of the modeled salinity field. The experiments indicate that when estuarine discharge increases, net plume mixing decreases in a rotating environment but increases in a nonrotating environment. Scaling analysis supports that this opposite trend in behavior is related to rotation turning the plume, limiting the lateral expansion and suppressing shear mixing. The results of this study explain different trends in net plume mixing reported in previous studies and compare favorably to observations of the Fraser River plume.

In the current context, nanotechnology plays a crucial role in improving fuel efficiency by employing engine oil-based nanoparticles, thus reducing machine wear and tear. Unlike previous studies, this work integrates the combined impacts of Cogley radiation, chemical reactions, and heat source with Hall current effects on the motion of copper and aluminum oxide MHD nanofluids in a rotating environment, which extends the understanding of thermophysical behavior of heat transfer processes in nanofluids. The base fluid chosen for this study is the Brinkman-type engine oil (EO). Analytical solutions are derived using the Laplace transform technique from the governing boundary value problem. Key findings include enhanced primary momentum with Brinkman parameters, diminished secondary momentum with Hall current, and the influence of radiation on temperature profiles. Numerical evaluations of engineering coefficients are presented, and the validity of our findings is confirmed by comparing them with prior studies, in specific cases. This research is crucial for advancing energy-efficient and reliable systems, with applications in critical fields such as automotive cooling, aerospace lubrication, and MHD generators, particularly in areas requiring precise control of heat and mass transfer.

Focusing on the issue of attitude tracking for low-cost and small-size Micro-Electro-Mechanical System (MEMS) Inertial Measurement Unit (IMU) in high dynamic environment, an Adaptive Unscented Kalman Filter (AUKF) method combining sensor fusion methodology with Artificial Neural Network (ANN) is proposed. The different control strategies are adopted by fusing multi-MEMS inertial sensors under various dynamic situations. The AUKF attitude determination approach utilizing the MEMS sensor and Global Positioning System (GPS) can provide reliable estimation in these situations. In particular, the adaptive scale factor is used to adaptively weaken or enhance the effects on new measurement data according to the predicted residual vector in the estimation process. In order to solve the problem that the new measurement data is not available in case of GPS fault, an attitude algorithm based on Radial Basis Function (RBF)-ANN feedback correction is proposed for AUKF. The estimated deviation of predicted system state can be provided based on RBF-ANN in GPS-denied environment. The corrected predicted system state is used for the estimation process in AUKF. An experimental platform was setup to simulate the rotation of the spinning projectile. The experimental results show that the proposed method has better performance in terms of attitude estimation than other representative methods under various dynamic situations.

An investigation of unsteady hydromagnetic natural convection heat and mass transfer flow with Hall current of a viscous, incompressible, electrically conducting, heat absorbing and optically thin radiating fluid past an accelerated moving vertical plate through fluid saturated porous medium in a rotating environment is carried out when temperature of the plate has a temporarily ramped profile. The exact solutions of momentum, energy and concentration equations are obtained in closed form by Laplace transform technique. The expressions of skin friction, Nusselt number and Sherwood number are also derived. For both ramped temperature and isothermal plates, Hall current tends to accelerate primary and secondary fluid velocities whereas heat absorption and radiation have reverse effect on it. Rotation tends to retard primary fluid velocity whereas it has a reverse effect on secondary fluid velocity. Heat absorption and radiation have tendency to enhance rate of heat transfer at the plate.

Energy harvesting within rotating environments can help to enable self-powered wireless sensing, which has been motivated in recent years by the advent of legislations mandating tyre pressure monitoring systems for automotive wheels. The centripetal acceleration (a = ωr2) within such rotational systems can attain 1,000's of g, which manifest as artificial gravity and can adversely suppresses the dynamic motion of oscillators. This paper investigates the possibility of using the high g conditions as a means of introducing nonlinear bi-stability, which can then allow an oscillator to benefit from a broadband response as well as mechanical amplification achieved from the bi-stable snap-through states. An experimental proof-of-concept prototype was designed, built and tested. By controlling the rotational speed ω of the apparatus, the masses of oscillators experienced a g-force of up to 90 g. Purely by increasing ω, an increase in transducer output was observed from the predicted amplification effect. However, beyond a certain threshold, output dropped to minimal as the potential barrier reached an insurmountable level. This work validates the proposed new mechanism that taps into the high g environment and opens a new avenue of design for vibration energy harvesting within rotational systems.

This paper presents a rotary power scavenging unit comprised of two systems of flexible beams connected by two masses which are joined by means of a spring, considering a PZT (QP16N, Midé Corporation) piezoelectric sheet mounted on one of the beams. The energy harvesting (EH) system is mounted rigidly on a rotating hub. The gravitational force on the masses causes sustained oscillatory motion in the flexible beams as long as there is rotary motion. The intention is to use the EH system in the wireless autonomous monitoring of wind turbines under different wind conditions. Specifically, the development is oriented to monitor the dynamic state of the blades of a wind generator of 30 KW which rotates between 50 and 150 rpm. The paper shows a complete set of experimental results on three devices, modifying the amount of beams in the frame supporting the system. The results show an acceptable sustained voltage generation for the expected range, in the three proposed cases. Therefore, it is possible to use this system for generating energy in a low-frequency rotating environment. As an alternative, the system can be easily adapted to include an array of piezoelectric sheets to each of the beams, to provide more power generation.