Periodic Flow Research Articles

Identification and Establishing Floral Calendar in Jimma Zone of Oromia Ethiopia

Bee flora resources are crucial for the development of beekeeping. The study aimed to find and construct a flowering calendar for bee plants in order to produce many batches of honey. Data were collected through bee plant inventory, pollen collection and honey pollen analysis. Based on bee plant inventories, pollen load collection, and honey pollen analysis, 103 plant species were identified as nectar and pollen sources for honeybees. Ageratum conizoides, Guizotia scabra, Cordia africana, Datura arborea, Plantago lanceolata, Rumex nervosus, and Justicia schimperiana were the most common honey-producing plants in the area. The fresh weight of pollen gathered at various months of the year revealed that a substantial amount of pollen was collected in September, October, and November, but the incoming pollen weight decreased in March and July. The area's peak honey flow period began in November and lasted until early December or late February. The modest honey flow also occurred in May and June. Pollen examination of honey samples indicated three monofloral honey types: Guizotia spp., Vernonia, and Croton monofloral honey types, with pollen frequencies ranging between 45% and 100%. The study indicated that the floral calendar of bee forages is completely reliant on the seasonal availability of food sources, and beekeepers should be aware of how to manage honeybee colonies in accordance with the flowering calendar in their area in order to enhance the frequency of honey production.

Periodicity and chaos of thermal convective flows in annular cylindrical domains using the method of isolation by spectral expansions

The dynamical and chaotic behaviors of natural convection flow in the semi-annular and full-annular cylindrical domains are studied using the method of isolation by spectral expansion. For each of the flow cases, spectral models with different orders are obtained and dynamical characteristics of the flow are investigated using numerical simulations. For the semi-annular case of study, results reveal that in all the generated spectral models, chaotic solution appears, but the onset of chaos between each system requires different set of control parameters. Bifurcation diagrams are provided for all the systems which show the ranges of periodic and chaotic behavior of the flow. Strange attractors are captured for all the systems with different orders. For the lowest-order model, a Lorenz-like attractor is produced, which has two distinguishable scrolls similar to Lorenz's famous attractor and for the other high-order models, the shape of strange attractor gets different. For the full-annular case of study, the physical characteristics of the flow are obtained. The results show that the produced thermal plume on the top of annulus gets higher fluctuations as the flow Rayleigh number gets higher. At a specific Rayleigh number, the flow behavior gets completely unstable, which shows a transitional regime change. At this state of flow, the domain is dominated by several vortices.

Transition of natural convection on a cooled circular surface with heated annular extension

Transition of natural convection on a circular cooled surface with heated annular extension is investigated in the present study by numerical simulation. Flow features and regimes of natural convection on the surface are studied for which the cooling and heating Rayleigh numbers (Rac and Rah) vary from 1 to 106 with air as the working fluid (Prandtl number of 0.71) at a fixed geometrical aspect ratio of 1 (heating characteristic length/cooling characteristic length). Three steady states revealed by numerical results include steady plume flow, steady dome flow and steady crown flow, which are corresponding to different dynamic regimes: a positive buoyancy dominated regime, a transitional regime and a negative buoyancy dominated regime. Besides, the dynamics behaviors in those steady regimes are scaled and validated by numerical results. The transition route of natural convection on the cooled circular surface with heated annular extension to the unsteady flow is also characterized in the case of Rac/Rah = 1. It has been demonstrated that the steady regime is followed by the unsteady regime. The periodic puffing flow, quasi-periodic flow, and chaotic flow are present in the unsteady regime. In addition, heat transfer in different regime flows is quantified.

Effects of Home-based Remote Cardiac Rehabilitation on Left Ventricular Function and Fear of Exercise in Patients after Percutaneous Coronary Intervention (PCI): A Retrospective Cohort Study

Aim: This study aims to explore the effects of home-based remote cardiac rehabilitation on left ventricular function and exercise fear in patients after percutaneous coronary intervention (PCI). Methods: A total of 232 patients with coronary heart disease after PCI treated in Tianshan Traditional Chinese Medicine Hospital from January 2020 to December 2022 were retrospectively analyzed. The patients were divided into the remote rehabilitation group (169 cases) and the routine group (63 cases) according to the exposure factor (home-based remote cardiac rehabilitation). Changes in left ventricular function and sports phobia Tampa Scale in patients with coronary heart disease after PCI were compared using propensity score matching to reduce selection bias and confounding factors. Results: After the intervention, the scores of patients in the tele-rehabilitation group were significantly higher than those in the conventional group in terms of fear of movement, perception of danger, fear of movement, avoidance of movement, and dysfunction (p-value < 0.05). Left heart function was compared between the tele-rehabilitation group and the conventional group. Patients in the tele-rehabilitation group had significantly higher peak mitral valve blood flow in the early diastolic period (E), peak mitral valve blood flow in the late diastolic period (A), six-minute walk test (6MWT), and ratio of the peak mitral valve blood flow in the early diastolic period to the peak mitral valve blood flow in the late diastolic period (E/A) than those in the conventional group (p-value < 0.05). However, the peak deceleration time and isovolumic diastolic time in the early mitral valve diastolic period were significantly higher in the tele-rehabilitation group than in the conventional group (p-value < 0.05). Conclusions: Home-based remote cardiac rehabilitation instruction can improve the heart function and exercise fear state of patients after PCI.

The appearance of oscillatory flows within a horizontal packed bed partly heated from below

We report on a numerical investigation of the unsteady mixed convective flow in a channel through a horizontal porous layer under localised isothermal heating from below to probe the oscillatory flow and thermal characteristics. The study was carried out for water flow within a plane channel containing stainless steel spherical particles. For this study, the channel height/particle diameter ratio was H/d=100 and the porosity was ɛ=0.35. The effects of the imposed pressure-driven flow characterised by the Péclet number (0.1≤Pe≤1000), and heating represented by the Rayleigh number (105≤Ra≤2×107), are investigated. The results reveal that for low Péclet numbers, steady free convective flows are dominant, while for high Péclet numbers, steady forced convective flows dominate. Importantly, no oscillatory flows are found to develop in the free and forced convection regimes. However, for moderate Péclet numbers, oscillatory mixed convective flows occur with different periodic, quasi-periodic, and chaotic flow behaviours. In addition, for low Rayleigh numbers, Ra≤106, the Nusselt number is not influenced by the Péclet number for Pe≤1. Nevertheless, for high Rayleigh numbers, Ra≥2×106, it is observed that there always exists a critical Péclet number for which the Nusselt number is a minimum. The effects of the Péclet and Rayleigh numbers on the local and average temperature disparity between the fluid and solid phases are then investigated.

Viscoelastic confinement induces periodic flow reversals in active nematics.

We use linear stability analysis and hybrid lattice Boltzmann simulations to study the dynamical behavior of an active nematic confined in a channel made of viscoelastic material. We find that the quiescent, ordered active nematic is unstable above a critical activity. The transition is to a steady flow state for high elasticity of the channel surroundings. However, below a threshold elastic modulus, the system produces spontaneous oscillations with periodic flow reversals. We provide a phase diagram that highlights the region where time-periodic oscillations are observed and explain how they are produced by the interplay of activity and viscoelasticity. Our results suggest experiments to study the role of viscoelastic confinement in the spatiotemporal organization and control of active matter.

Calculation of the parameters and characteristics of a rotating lunar jet penetrator

The purpose of the work is to determine the parameters of the internal ballistics of a solid fuel jet engine mounted on a jet penetrator entering the ground at a high rotation speed around its own axis. Research methods: to determine the pressure in the chamber of a rotating engine, the known equations for the balance of gas inflow and consumption are usually used, as in the case of a non-rotating solid fuel jet engine. The difference between the internal ballistics of a rotating solid fuel jet engine is that the effect of rotation on the operating process is taken into account by the coefficient of gas flow from the chamber of the rotating engine; a change in the rate of erosive combustion of solid fuel during rotation of a solid fuel jet engine; heat loss coefficient. Results: it was found that the parameters of the internal ballistics of rotating jet engines of solid fuel are mainly influenced by the coefficient of gas flow from the chamber of the rotating engine; effect of erosive combustion of solid fuel and change in heat loss coefficient. The main calculated dependencies for determining the pressure in the combustion chamber of a rotating solid fuel engine are presented for periods when the pressure reaches a stationary mode of operation of the engine, operation of the engine in a stationary mode and during the period of free flow of gases from the chamber of a solid fuel jet engine. A method for selecting the linear and angular dimensions of a rotating engine nozzle is presented. An estimate of the thrust force for a single nozzle rotating solid fuel jet engine is given. It has been established that the magnitude of the thrust force of rotating engines (under other identical conditions in the combustion chamber) is 1.1–1.36 times less than that of non-rotating solid fuel jet engines. The experiments carried out showed a decrease in the degree of swirl of the gas flow of rotating solid fuel engines with an increase in the number of fuel pellets in the engine charge. Conclusion: the results presented in the article can be useful for scientists, graduate students and engineers involved in the creation and operation of aviation and rocket and space technology, and can also be useful for students of technical universities studying in relevant specialties.

Improved Spatiotemporal Distributions of Sweeping Jet Film Cooling With a Shaped Exit Design

Abstract Sweeping jet (SJ) is a self-excited flow control device that can generate continuous and periodic flow, which makes it a promising geometry for film cooling. However, the cooling performance of current SJ configurations is not significantly better than that of 777-shaped holes. This paper presents two modified SJ configurations, named shaped SJ1 and shaped SJ2, which possess distinct shaped exit geometries. The spatiotemporal coolant distributions were comprehensively quantified for the 777-shaped hole, the compact SJ (with compact geometry), the shaped SJ1, and the shaped SJ2. The instantaneous cooling effectiveness distributions of the four configurations at blowing ratios (M) ranging from 0.5 to 3.0 were measured using the fast pressure-sensitive paint technique. The shaped SJ2 integrated the cooling characteristics of the 777-shaped hole and SJ. It maintained stability at a relatively low M, while began to oscillate when M was increased above 1.5. The shaped SJ design exhibited superior cooling effectiveness at both low and high M of 0.5 to 3.0. A proper orthogonal decomposition analysis and simulations illustrated the oscillation processes and flow structures within the SJ configuration. The shaped SJ2 showed a reduced outlet momentum and a more even distribution of film coverage than the 777-shaped hole, resulting in considerably improved cooling performance.

Microgeographic speciation in a complex of Anatolian bush crickets facilitated by fast evolution of reproductive isolation.

Identifying the drivers of microgeographic speciation (i.e., speciation over small, local geographic scales) is key to understand the origin of speciose groups. Here, we use genomic data to infer the demographic processes underlying diversification in Poecilimon luschani (Orthoptera: Tettigoniidae), a species complex belonging to the most diverse genus of bush crickets from the Mediterranean region (>170 taxa) that comprises three recognized subspecies with small allopatric distributions in the topographically complex Teke Peninsula, southwestern Anatolia. Phylogenomic reconstructions that include all other taxa within the species group confirmed that subspecies of P. luschani originated from a common ancestor during the Pleistocene, supporting recent (<1 Ma) diversification within a small geographical area (ca. 120 × 80 km). Genetic clustering analyses corroborated the distinctiveness of each subspecies and the cohesiveness of their respective populations, with abrupt genetic discontinuities coinciding with contemporary range boundaries. Indeed, our analyses uncovered the presence of two sympatric cryptic sister lineages that diverged <300 ka ago and do not admix despite being co-distributed. Collectively, these results support that all lineages within the complex represent independently evolving entities corresponding to full-fledged species. Statistical evaluation of alternative models of speciation strongly supports a scenario of divergence in isolation followed by a period of limited gene flow during the last glacial period, when all lineages experienced marked expansions according to demographic reconstructions. Our study exemplifies how localized allopatric divergence and fast evolution of reproductive isolation can promote microgeographic speciation and explain the high rates of endemism characterizing biodiversity hotspots.

Simulated hydrological effects of grooming and snowmaking in a ski resort on the local water balance

Abstract. The presence of a ski resort modifies the snow cover at the local scale, due to snow management practices on ski pistes, especially grooming and snowmaking. Snow management exerts 2-fold effects on the local hydrological cycle, through (i) abstraction and transfer of water used for snowmaking, and (ii) changes in water runoff due to added snow mass through snowmaking and/or delayed melting of the snowpack due to snow grooming. This induces a local pressure on water resources, which has seldom been addressed in scientific studies hitherto. Here we introduce a method to compute the hydrological effects of snow management on ski pistes and we apply and illustrate its results for the case study of the La Plagne ski resort in the Northern French Alps. The approach mainly relies on snow cover modelling using the Crocus snow cover driven by SAFRAN reanalysis and climate projections. Model results are evaluated against in-situ hydrological observations and show that the modelling approach, although very simplified for many hydrological processes, provides relevant information and insights in terms of the influence of snow-related processes on water resources. Our study shows a visible impact of grooming, virtually eliminating snowmelt in winter, thus delaying the onset of snowmelt. This results is a lower snowmelt flux during the wintertime, low flow period, on the order of −10 % to −20 %, compensated by higher amounts when snow melts. While about 10 % of the water used for snowmaking is estimated to be lost by evaporation through the ice formation process from the liquid water droplets, we find that, in the case studied, the annual scale alteration of water resources is limited and estimated to be on the order of 1 % to 2 %. This is due to the fact that the amount of water used for snowmaking on ski pistes represents a fraction of 10 % to 20 % of total annual precipitation, that ski pistes cover typically 10 % of the surface area of catchments within which ski resorts are located, and that snowmaking equipment covers, in the case of La Plagne, 40 % of the surface area of ski pistes. Therefore, in this case, snowmaking mainly leads to a moderate shift in snow cover formation and snowmelt processes and plays, for example, a smaller role than the influence of future climate change on mountain hydrology. This study provides an initial overview of the influence of grooming and snowmaking on river flows in a mountain catchment, which can inform future studies on water management and climate change adaptation in areas with ski tourism facilities. This study does not discuss long-term sustainability challenges of ski tourism and other aspects of the local environmental impacts (landscape, biodiversity) of snow management, such as the construction and use of mountain water reservoirs and other earthworks in ski resorts.

Routing and scheduling co-design for holistic software-defined deterministic network

As a result of the growing complexity of industrial Internet applications, traditional hardware-based network designs are encountering challenges in terms of programmability and dynamic adaptability as they struggle to meet the real-time, high-reliability transmission requirements for the vast quantities of data generated in industrial environments. This paper proposes a holistic software-defined deterministic network (HSDDN) design solution. This solution uses a centralized controller to implement a comprehensive software definition, ranging from the network layer down to the physical layer. Within the wireless access domain, we decouple the standard radio-frequency modules from baseband processing to realize a software-defined physical layer, which then allows us to adjust the data transmission cycles and tag the trigger rates to meet demand for low-power, high-concurrency transmission. Within the wired network domain, we integrate software-defined networking with time-sensitive networking and propose a coordinated design strategy to address routing and the deterministic scheduling problem. We define a set of constraints to ensure collaborative transmission of the periodic and aperiodic data flows. To guarantee load balancing across all paths and timeslots, we introduce the Jain’s fairness index as the optimization objective and then construct a nondeterministic polynomial-time (NP)-hard joint optimization problem. Furthermore, an algorithm called Tabu search for routing and scheduling with dual-stages (TSRS-DS) is proposed. Simulation experiments demonstrate the effectiveness of the proposed HSDDN architecture.

Oscillatory electro-magneto-kinetics of confined-Stokes-second-problem micro-flows

We semi-analytically investigate the electro-magneto-hydrodynamics of time periodic electroosmotic flow of a Newtonian electrolyte through microchannels with oscillating boundaries, resembling a confined-Stokes-second-problem type system. Herein, a constant orthogonal magnetic field and a constant transverse electric field have been used along with the driving time periodic electric field to have better control over mixing in the microchannel or to augment the pumping. The Poisson–Boltzmann equation has been solved with Debye–Hückel linearization for the thin electric double layer to obtain the electric potential distribution. We determine the flow field for low Hartmann number (Ha) cases by the regular perturbation method. Furthermore, Laplace transformation has been used to solve the flow field for each order in the obtained perturbation series. We have obtained the solution of flow field up to O(Ha) and found an excellent match with the complete numerical solution for our range of Ha. The dependence of flow field on dimensionless parameters, such as Ha, electrokinetic number (M), and Womersley number (Wo), has been discussed thoroughly, where Ha and M are functions of the strength of applied magnetic field and transverse electric field, respectively, and Wo is the function of Debye length, kinematic viscosity, and frequency of the time periodic electric field. Interestingly, for large values Wo, we find wave like motion in the flow field, which induces vorticity as well as better mixing caliber. Additionally, we find that the interplay between Ha and M controls the mixing and modifies the flow rate according to the need. Various combinations of such parameters have been discussed to promote mixing as well as pumping for such strongly coupled microfluidic phenomena.

Sharp uniform-in-time mean-field convergence for singular periodic Riesz flows

We consider conservative and gradient flows for N -particle Riesz energies with mean-field scaling on the torus \mathbb{T}^d , for d\geq 1 , and with thermal noise of McKean–Vlasov type. We prove global well-posedness and relaxation to equilibrium rates for the limiting PDE. Combining these relaxation rates with the modulated free energy of Bresch et al. (2019, 2019–2020, 2020) and recent sharp functional inequalities of the last two named authors for variations of Riesz modulated energies along a transport, we prove uniform-in-time mean-field convergence in the gradient case with a rate which is sharp for the modulated energy pseudo-distance. For gradient dynamics, this completes in the periodic case the range d-2\leq s&lt;d not addressed by the previous work Rosenzweig and Serfaty (2023). We also combine our relaxation estimates with the relative entropy approach of Jabin and Wang (2018) for so-called \dot{W}^{-1,\infty} kernels, giving a proof of uniform-in-time propagation of chaos alternative to Guillin et al. (2021).

ЭФФЕКТИВНОСТЬ МОДЕЛИРОВАНИЯ СТОКА РЕК БАССЕЙНА ВЕРХНЕЙ УССУРИ С ИСПОЛЬЗОВАНИЕМ ДАННЫХ НАБЛЮДЕНИЙ И РЕАНАЛИЗА ERA5

Experience of using meteorological observations and the ERA5 reanalysis for runoff modeling using the GR4J conceptual model is outlined. The study objects are catchments within the Ussuri River basin (Kirovskii, the Russian Far East). The results of the comparison of ground-based observations and reanalysis data are presented. The hydrological model has been calibrated and verified on the basis of various data sources. The traditional scores NSE, logNSE, and BIAS have been used to evaluate the modeling efficiency. According to the scores, the modeling efficiency is generally “satisfactory” and better. It is shown that for simulations, it is better to use observation network data in case of floods and the reanalysis data in case of spring high water and low flow periods. It is concluded that the effective resolution of the ERA5 data for daily precipitation and air temperature for hydrological modeling in the study area is 0.75°-1.0° (~90-120 km).

Heat source/sink impact on wave oscillations of thermal and concentration boundary layer along inclined plate under lower gravitational region

The force of attraction between two masses increases as gravity increases. Gravity is very important mechanism for mass transfer characteristics across the inclined shape. The significant purpose of current study is to examine amplitude in mass transfer under reduced gravity-driven flow. The impact of heat source/sink on periodic mixed convective gravity-driven flow across the inclined plate has been evaluated. The oscillatory characteristics of heat rate and mass transmission are explored at three inclined angles π/6, π/4 and π/3. The gravity is assumed under maximum temperature difference. The governing dimensional model is transformed into non-dimensional equations with appropriate scaling variables. The non-dimensional equations are again reduced in non-oscillatory, real and imaginary parts. For smooth coding, the primitive formulation is used with finite difference method to change non-dimensional forms in algebraic system. The algebraic equations are solved with Gaussian elimination scheme to display velocity field, temperature distribution and rate of concentration numerically. The impact of heat source/sink ±δ, reduced gravity Rg, buoyancy variable λT, modified buoyancy factor λC, Prandtl factor Pr, reduced gravitation factor Rg, and Schmidt variable Sc on the oscillating behavior of shear stress, rate of fluctuating heat transfer, and rate of fluctuating mass transfer is secured. It is found that the amplitude of fluid velocity and temperature increases for each parameter under heat source +δ=0.4. It can be seen that concentration distribution increases as reduced gravity Rg increases under heat sink −δ=0.3. It can be seen that amplitude of shearing stress and heat transfer increases as heat source +δ increases. It is obtained that oscillation in mass transfer increases as heat source/sink ±δ increases under reduced gravitation Rg=1.2.

Characteristics of local flow structure with different particle properties in a gas-solid diameter-varying fluidized bed

The effects of particle property on gas-solid flow in the diameter-varying riser are experimentally examined using the optical fiber probe in this research. Local flow features are obtained by signal analysis method under the operating conditions of 3–7 m/s and 8–63 kg/m2s. The results show that solid holdup distribution of glass beads is wider than that of catalyst particle particles in the wall region but is narrow in the center region. Solid holdup fluctuations tend to decrease with the increase of particle density under low-concentration conditions but increase at high-concentration conditions. The results from power spectrum density (PSD) show that the increase in particle density strengthens the periodic flow features in the enlarged section. The motion intensity decreases at the particle level but increases at the cluster level for high-density particles. Additionally, as particle density rises, the solid concentration discrepancies between the straight section and the enlarged section widen. In contrast to the upper straight section, the effects of particle density on gas-solid flow are minimal in the enlarged section.

Sedimentary porewaters record regional tectonic and climate events that perturbed a deep-sea brine pool in the Gulf of Aqaba, Red Sea

Brine pools in deep-sea environments provide unique perspectives into planetary and geological processes, extremophile microbial communities, and sedimentary records. The NEOM Brine Pool Complex was the first deep-sea brine pool system found in the Gulf of Aqaba, representing a significant extension of the geographical range and depositional setting of Red Sea brine pools. Here, we use a combination of brine pool samples collected via cast using a conductivity, temperature, depth instrument (CTD), as well as interstitial porewaters extracted from a sediment core collected in the NEOM Brine Pool to characterize the chemical composition and subsurface evolution of the brine. New results indicate that the NEOM brines and the subsurface porewaters may originate from different sources. Elemental concentrations suggest the brines in the NEOM pool are likely derived from dissolution of sub-seabed evaporites. In contrast, the sedimentary porewaters appear to have been influenced by periodic turbidite flows, generated either by earthquakes, submarine landslides, or flash floods, in which normal marine waters from the overlying Red Sea became entrained, periodically disturbing the chemistry of the brine pool. Thus, sediment porewaters beneath brine pools may record transient and dynamic changes in these deep marine depositional environments, reflecting the interplay between climate, tectonics, and sedimentation patterns along a rapidly urbanizing coastline. In concert, new results from NEOM extend the range and chemical constraints on Red Sea Brine Pools and highlight the dynamic interplay between Red Sea Deep water, dissolving evaporites, turbidites, and subsurface fluids that produce these unique depositional environments which host microbial life at the edge of habitability. In concert with sedimentological indicators, the chemistry of porewaters beneath deep-sea brine pools may present detailed records of natural hazards arising from interactions between the atmosphere, lithosphere, hydrosphere, and anthroposphere.

Stability optimization of periodic mass flow rate fluctuation in the variable diameter extension screw

Screw conveyors are widely used in conveying bulk solid materials, and higher conveying stability is required for product uniformity and weighing accuracy. The purpose of this paper is to improve particle conveying stability in screw feeders. The characteristics of particle mass flow rate (MFR) are investigated to reveal the periodic fluctuation mechanism. Different screw structures are designed to reduce MFR fluctuation and improve conveying stability. Results show that the optimal conveying stability occurs when the variable diameter extension (VDE) is twice the pitch length and the diameter reduction ratio is 0.92, which is verified by experimental data. Compared with the standard screw, the MFR fluctuation relative standard deviation of the VDE screw decreases from 29.79 % to 2.03 %. Moreover, the particle force on the screw feeding device casing is indicated. The larger average compressive force of particles on the device wall significantly increases the device damage probability and particle agglomeration.

Volume compensation of large-deformation 3D-printed soft elastomeric elastocaloric regenerators

Elastomeric elastocaloric regenerators have great potential for use in low-stress elastocaloric cooling devices. However, these regenerators display an asymmetric fluid exchange when operating in an active elastocaloric cooling cycle, due to the large required strains and associated volume change. During strain, the fluid volume increases, which passively forces fluid flow into the regenerator; when the strain is released, the fluid volume decreases, which results in a fluid flow out of the regenerator. During a traditional elastocaloric cooling cycle, there are also active fluid flow periods provided by fluid displacers or pumps. Here, we study the passive fluid flow in high-strain regenerators using a numerical model and experiments in two types of regenerators. Hyperelastic models are used to fit the experimentally measured mechanical behavior of thermoplastic polyurethane elastocaloric elastomers, and the model is subsequently used to conduct finite-element simulations predicting regenerator volume changes for an applied strain of 200%–600%. We validated the results using a specifically designed setup for measuring volume changes using pressure differences on a parallel-plate regenerator. For a strain range of 200%–600%, the predicted volume change ratio is 69.5%, closely matching the experimental value of 66.7%. We observed that the middle region of the regenerator experiences a higher volume change, which can be accurately accounted by the numerical model.

Optimal waveform for fast synchronization of airfoil wakes

We obtain an optimal actuation waveform for fast synchronization of periodic airfoil wakes through the phase reduction approach. Using the phase reduction approach for periodic wake flows, the spatial sensitivity fields with respect to the phase of the vortex shedding are obtained. The phase sensitivity fields can uncover the synchronization properties in the presence of periodic actuation. This study seeks a periodic actuation waveform using phase-based analysis to minimize the time for synchronization to modify the wake shedding frequency of NACA0012 airfoil wakes. This fast synchronization waveform is obtained theoretically from the phase sensitivity function by casting an optimization problem. The obtained optimal actuation waveform becomes increasingly non-sinusoidal for higher angles of attack. Actuation based on the obtained waveform achieves rapid synchronization within as low as two vortex shedding cycles irrespective of the forcing frequency, whereas traditional sinusoidal actuation requires ${O}(10)$ shedding cycles. Further, we analyse the influence of actuation frequency on the vortex shedding and the aerodynamic coefficients using force-element analysis. The present analysis provides an efficient way to modify the vortex lock-on properties in a transient manner with applications to fluid–structure interactions and unsteady flow control.