Individual Jets Research Articles

Quasi-geostrophic monopoles in sheared zonal jets and multiple-jet flows

This work continues our earlier studies of the interaction between a monopolar vortex and a sheared zonal flow in the framework of a 1.5-layer quasi-geostrophic model, based on numerical experiments with singular vortices. Earlier examination of flows with shears of fixed sign showed that the interaction depends strongly on the latitudinal distribution of the gradient of background potential vorticity b(y) (y being the latitude). The latitude y0 at which b(y) changes sign turns out to be of particular importance. In the vicinity of y0, under certain conditions, there arises the zonal-strip region, which attracts (repels) prograde (retrograde) vortices. This effect is examined here for the zonal flows in the form of individual jets as well as for the systems of alternating zonal jets; in all these cases, the background-flow velocity shear and the parameter b(y) can change sign depending on y. It is shown that the vortex drifts to the nearest latitude y0 on the prograde side of the zonal flow, and the meridional speed of the trapped vortex almost vanishes, but its zonal speed is directed westward and approaches the Rossby-wave drift velocity.

Solar Jet Hunter: a citizen science initiative to identify and characterize coronal jets at 304 AA

Solar coronal jets seen in extreme ultraviolet (EUV) are ubiquitous on the Sun, and they have been found in and at the edges of active regions, at the boundaries of coronal holes, and in the quiet Sun. Jets have various shapes, sizes, brightness, velocities, and durations in time, which complicates their detection by automated algorithms. So far, solar jets reported in the Heliophysics Event Knowledgebase (HEK) have been mostly reported by humans looking for them in the data, with different levels of precision regarding their timing and positions. We created a catalog of solar jets observed in EUV at 304 \ containing precise and consistent information on the jet timing, position, and extent. We designed a citizen science project, Solar Jet Hunter, on the Zooniverse platform, to analyze EUV observations at 304 \ from the Solar Dynamic Observatory/Atmospheric Imaging Assembly (SDO/AIA). We created movie strips for regions of the Sun in which jets have been reported in HEK and ask the volunteers to 1) confirm the presence of at least one jet in the data and 2) report the timing, position, and extent of the jet. We report here the design of the project and the results obtained after the analysis of data from 2011 to 2016. We note that 365 "coronal jet" events from HEK served as input for the citizen science project, equivalent to more than 120,000 images distributed into 9,689 "movie strips." Classification by the citizen scientists resulted in 883 individual jets being identified. We demonstrate how citizen science can enhance the analysis of solar data with the example of Solar Jet Hunter. The catalog of jets thusly created is publicly available and will enable statistical studies of jets and related phenomena. This catalog will also be used as a training set for machines to learn to recognize jets in further datasets.

Short-period flow oscillation during eruptions of Onikobe geyser, NE Japan: Insights from thermal infrared observation and acoustic measurements

Geysers are episodic features with variable eruption intervals that range from minutes to years. Although many previous studies on geysers have focused on subsurface properties and processes such as plumbing geometry and recharge process, it is known that erupting fluid column exhibits short-term behaviors such as individual water jets from the vent. In the present study, we conducted observations at Onikobe geyser, NE Japan, a relatively small geyser (geysering well) erupting water up to ∼6–8 m every ∼10 min and observed the erupting fluid column using a thermal infrared camera and an acoustic sensor. We succeed in tracking the water jets by analyzing spatio-temporal temperature map obtained from the thermal infrared observation, which clearly shows the eruptions at Onikobe geyser are not completely stationary but rather a series of intermittent jets with a short period interval of <1 s. We estimate the exit velocity by fitting a ballistic model under the air drag condition of inertial resistance to the jet trajectory. The exit velocity and the averaged gas volume fraction of the erupting fluid are estimated to be ∼4–79 m/s and ∼0.93–0.96, respectively. The exit velocity is ∼30 m/s during the first bursts, then it rapidly increases to ∼50–80 m/s for ∼15 s, and then decreases to ∼20–30 m/s until ∼10 s before the eruption ends. Time series analyses of the thermal infrared and acoustic signals during an eruption indicate harmonic spectra with integer multiple peaks. The fundamental frequency showing ∼4 Hz at the beginning gradually decreases to ∼2 Hz for ∼15 s, keeps almost constant in the following 30 s, and then slightly increases near the end of the eruption. These harmonic spectra may be caused by a resonance mechanism, non-linear fluid motion, and/or subsurface two-phase flow. We discuss the case of a closed organ-pipe resonance in a subsurface crack and attribute the frequency decrease to a decrease in the water level in the crack (an increase in the length of the resonating liquid-vapor column) and/or a decrease in the gas volume fraction of the liquid-vapor mixture in the crack. Since such harmonic characteristics are observed at other geysers, further simultaneous observation of the short-period oscillations on the erupting column proposed in this study with seismic observations of harmonic tremor may provide an improved understanding of geyser subsurface phenomena.

Research On Soil Displacement Prediction Method Caused By High-pressure Jet Grouting Pile Group Construction Under Adjacent Pile Response

This paper analyzes the soil displacement effect during high-pressure jet grouting pile construction by simplifying the construction process as a series of pressure-controlled spherical cavity expansions in a semi-infinite soil medium. Based on the elastic-plastic solution of pressure-controlled spherical cavity expansion theory, a calculation method is proposed to estimate the soil displacement caused by high-pressure jet grouting pile construction. Non-linear contact theory between the pile and soil is introduced, and the finite difference method is employed to determine the internal forces and deformations of the pile. The proposed method is applied to field construction cases, and its validity is verified by comparing the results with on-site monitoring data. The research findings reveal that the soil displacement effect decreases with depth and primarily occurs in shallow soil layers during the construction of individual high-pressure jet grouting piles. The lateral displacement at the ground surface increases first and then decreases with the increase in horizontal distance, while the ground uplift exhibits an exponential decay trend.

Proper motion of the radio jets in two blazars at redshift above 3

ABSTRACT There is still a limited number of high-redshift (z &amp;gt; 3) active galactic nuclei (AGNs) whose jet kinematics have been studied with very long baseline interferometry (VLBI). Without a dedicated proper motion survey, regularly conducted astrometric VLBI observations of bright radio-emitting AGN with sensitive arrays can be utilized to follow changes in the jets, by means of high-resolution imaging and brightness distribution modelling. Here, we present a first-time VLBI jet kinematic study of NVSS J080518 + 614423 (z = 3.033) and NVSS J165844 − 073918 (z = 3.742), two flat-spectrum radio quasars that display milliarcsecond-scale jet morphology. Archival astrometric observations carried out mainly with the Very Long Baseline Array, supplemented by recent data taken with the European VLBI Network, allowed us to monitor changes in their radio structure in the 7.6−8.6 GHz frequency band, covering almost two decades. By identifying individual jet components at each epoch, we were able to determine the apparent proper motion for multiple features in both sources. Apparent superluminal motions range $(1-14)\, c$, and are found to be consistent with studies of other high-redshift AGN targets. Using the physical parameters derived from the brightness distribution modelling, we estimate the Doppler-boosting factors (δ ≈ 11.2 and δ ≈ 2.7), the Lorentz factors (Γ ≈ 7.4 and Γ ≈ 36.6), and the jet viewing angles (θ ≈ 4.4° and θ ≈ 8.0°), for NVSS J080518 + 614423 and NVSS J165844 − 073918, respectively. The data revealed a stationary jet component with negligible apparent proper motion in NVSS J165844 − 073918.

DNS analysis of the effect of control parameters on the heat transfer performance of intermittently controlled impinging jets

Impinging jets are used industrially in various applications such as heating and cooling. However, multiple impinging jets (MIJ) create a complex flow field due to interference between the individual jets, which hinders heat transfer. In order to solve the problem of heat transfer performance in MIJ, a new control method must be developed. This study introduces intermittent control to 13 hexagonally arranged circular jets to investigate the possibility of control. In the intermittent control, the 13 jets are divided into three groups, and each group is intermittently issued. The distance between jets and the issuing period are changed as control parameters, and the heat transfer characteristics are evaluated using direct numerical simulation (DNS). The time-averaged velocity field revealed the effects of the intermittent period and the distance between jets on the flow characteristics, and the Nusselt number distribution on the wall surface indicated that the proposed method improves the heat transfer characteristics.

Investigation on different laser-powder alignments and their influence on part properties in high-speed Directed Energy Deposition

Efficient high-speed directed energy deposition via laser beam (HS DED-LB) requires precise knowledge of the powder focus location and diameter. The alignment of the laser and powder focus ensures maximum powder efficiency and minimizes potential defects caused by unmolten powder due to insufficient power input during the laser-powder interaction time. The focal characteristics, such as diameter or focus position, are dependent on the nozzle used and are affected by the powder gas jet parameters, like shielding gas- or carrier gas flow. This study analyses the effects of individual powder gas jet parameters on the focal position and -diameter. Additionally, the impact of different laser-powder alignments (unaligned and aligned) for HS DED-LB is investigated by adjusting the laser focus to the measured powder focus position. The analysis of these different settings focuses on the sample’s height, relative density, and microhardness.

General understanding on spray collapse process of an asymmetrical multi-hole direct injection gasoline injector under wide flash-boiling conditions

How the under-expansion impacts the flash-boiling spray collapse process over wide superheat levels ( Rp, defined as the ratio of saturation pressure to ambient pressure) is not well understood. In the present study, n-hexane flash-boiling sprays issued from a five-hole asymmetrical injector were experimentally and numerically studied to obtain a more general understanding of the spray collapse with wide Rp variation. The experimental results proved that the collapse in the transitional region occurs in the far field, unlike the fully collapse that occurred in the near-nozzle region. The numerical results demonstrated the complexity of individual jet evolutions and their interactions over wide Rp. For individual flash-boiling jets, there were different behaviors in the near-nozzle region. In the case with Rp slightly larger than 1, no shock waves can be observed, but a set of compression-expansion chains. The further increase in Rp caused the generation of shock waves, and resultantly the primary cells were established. For the multi-jet sprays, the further increase in Rp enlarged the primary cells, leading to their interactions and the generation of secondary cells. When Rp was sufficiently higher, the further interactions among primary and secondary cells could cause the generation of tertiary cell. Orderly interactions of shock cells were observed with increasing Rp, that is, the interactions initially occur between the adjacent jets with smaller distances, and then other jets were involved. Based on the results: It was found that the compression-expansion chains caused the low- Rp flash-boiling spray collapse in the far field; With the increase in Rp, the shock waves and shock-to-shock interaction become the main contributor to spray collapse, leading collapse appearing in the near-nozzle region.

Nectophore coordination and kinematics by physonect siphonophores.

Siphonophores are ubiquitous and often highly abundant members of pelagic ecosystems throughout the open ocean. They are unique among animal taxa in that many species use multiple jets for propulsion. Little is known about the kinematics of the individual jets produced by nectophores (the swimming bells of siphonophores) or whether the jets are coordinated during normal swimming behavior. Using remotely operated vehicles and SCUBA, we video recorded the swimming behavior of several physonect species in their natural environment. The pulsed kinematics of the individual nectophores that comprise the siphonophore nectosome were quantified and, based on these kinematics, we examined the coordination of adjacent nectophores. We found that, for the five species considered, nectophores located along the same side of the nectosomal axis (i.e. axially aligned) were coordinated and their timing was offset such that they pulsed metachronally. However, this level of coordination did not extend across the nectosome and no coordination was evident between nectophores on opposite sides of the nectosomal axis. For most species, the metachronal contraction waves of nectophores were initiated by the apical nectophores and traveled dorsally. However, the metachronal wave of Apolemia rubriversa traveled in the opposite direction. Although nectophore groups on opposite sides of the nectosome were not coordinated, they pulsed with similar frequencies. This enabled siphonophores to maintain relatively linear trajectories during swimming. The timing and characteristics of the metachronal coordination of pulsed jets affects how the jet wakes interact and may provide important insight into how interacting jets may be optimized for efficient propulsion.

The Perturbation of Ozone and Nitrogen Oxides Impacted by Blue Jet Considering the Molecular Diffusion

This study investigated the diffusion impact on the chemical perturbation of NOx and O3 caused by the streamer and leader parts of a blue jet in the low stratosphere (18–30 km), using the coupling of a detailed stratospheric chemistry model and a typical diffusion model. The study found that diffusion significantly impacted the evolution of chemical perturbations at both short-term and long-term time scales after the blue jet discharge, with changes in NOx and O3 concentrations observed at different altitudes (18–28 km). At 18 km, the concentrations of NOx and N2O that account for diffusion start to decrease after 1 s, whereas those without diffusion remain at their peak concentrations. Meanwhile, O3 is slowly destroyed with less NOx, rather than dropping to an unrealistic low value immediately after the discharge without diffusion. The perturbation caused by the blue jet discharge disappears within a few tens of seconds at 18 km when molecular diffusion is considered. At 30 km, the chemical perturbation from four point sources was observed through changes in NO2 concentrations. However, the total concentration of NO2 perturbed by the streamer part discharge at the given surface was negligible when considering diffusion. Overall, this study provided a useful model tool for a more accurate assessment of the chemical effects of individual blue jets.

Incoherent diffractive dijet production in electron DIS off nuclei at high energy

We study incoherent diffractive dijet production in electron-nucleus deep inelastic scattering at small ${x}_{\mathrm{Bj}}$ within the color glass condensate. We follow the general approach of [1] but we focus on the correlation limit, that is, when the momentum transfer ${\mathrm{\ensuremath{\Delta}}}_{\ensuremath{\perp}}$ and the gluon saturation momentum ${Q}_{s}$ of the nucleus are much smaller than the individual jet momentum ${P}_{\ensuremath{\perp}}$. We arrive at analytic expressions for the dijet cross section, which can be written as a sum of four terms which exhibit factorization: each such term is a product between a hard factor, which includes the decay of the virtual photon to the $q\overline{q}$ pair, and a semihard one which involves the dipole-nucleus scattering amplitude. We further calculate the azimuthal anisotropies $⟨\mathrm{cos}2\ensuremath{\phi}⟩$ and $⟨\mathrm{cos}4\ensuremath{\phi}⟩$. They are of the same order in the hard momentum ${P}_{\ensuremath{\perp}}$, but the $⟨\mathrm{cos}4\ensuremath{\phi}⟩$ is logarithmically suppressed due to its dependence on the semihard factor. Finally, in order to extend the validity of our result towards the perturbative domain, we calculate the first higher kinematic twist, i.e., the correction of relative order ${\mathrm{\ensuremath{\Delta}}}_{\ensuremath{\perp}}^{2}/{P}_{\ensuremath{\perp}}^{2}$.

Minimising Butadiene Level in Liquefied Petroleum Gas (LPG) via Non-Stirred Blending with Numerical Approach

LPG has variable commercial grades due to its varying LPG composition will yield different properties. Because their properties depend on the composition, the LPG quality will differ based on the source of its production extracted either from refinery streams or natural gas. The composition of propane and butane, which are the two major components in LPG composition, play an important role in reflecting the properties of LPG, as the mixtures influence the boiling points and also meet product specification requirements. Butadiene is also present in LPG, albeit in trace amounts. Although butadiene is a minor component, it must be kept minimised of the total weight fraction due to regulatory limits. Butadiene is a hazardous chemical that, when inhaled, can cause cancer and genetic defects. LPG used for commercial purposes that contain of any carcinogenic substance such as butadiene must also be classified as carcinogenic. The LPG plant operator is facing the problem that imported LPG composition from outside sources contain levels of butadiene that exceed the regulatory limit of 0.5% of weight fraction. LPG composition, containing butadiene levels that exceed 0.5% of weight fraction is considered as off-specification, while butadiene levels less than 0.5% of weight fraction are considered as on-specification the LPG products. To reduce the levels of butadiene that exceed 0.5% of the weight fraction in off-specification LPG products, the blending of on-specification LPG products with off-specification was introduced and provided the most economical method inside the plant. The jet mixing approach was selected to predict the homogeneous blending time for each different off-specification LPG composition because it is the best approximation for natural mixing behaviour. Four empirical mixing time correlations of jet mixing were applied for the prediction of homogeneous blending time; the correlations were derived by Lane and Rice (1982), Maruyama, Ban and Mizushina (1982), Grenville and Tilton (1997) and Hiby and Modigell (1978). The homogeneous blending time predicted by these four mixing time correlations decreased as the quantity of on-specification LPG required increased, which is in good agreement with both simulation results of 95% and 99% mixing. Therefore, due to the development of individual jet mixer correlation, these four mixing time correlation results in different homogeneous blending times was going through the different measurement techniques and monitoring methods in jet mixed tanks.

Simulation of jets induced by steam injection through multi-hole sparger using effective heat and momentum models

Direct contact condensation (DCC) of steam in the pressure suppression pool (PSP) is used to control containment pressure in Boiling Water Reactors (BWRs) and Advanced Pressurized Water Reactors (APWRs). The competition between momentum and heat sources induced by steam injection through multi-hole spargers and blowdown pipes determines whether the pool is thermally stratified or mixed. Development of thermal stratification affects capacity of the PSP to condense steam. To enable computationally efficient modeling of the PSP transients, the Effective Heat Source (EHS) and Effective Momentum Source (EMS) models have been proposed previously. The EHS/EMS models enable simulation of the large scale pool behavior without explicit modeling of the steam water interface and DCC phenomena. One of the problems for an optimal implementation of the EHS/EMS models is the definition of the boundary conditions that impose distribution of the momentum and heat sources. In this work, EHS/EMS models are implemented using “Unit Cell” approach in ANSYS Fluent to provide detailed numerical analysis of the individual turbulent jets induced by steam injection through the sparger holes. The model is validated against data from Particle Image Velocimetry (PIV) and temperature measurements for a range of steam injection conditions in the PANDA HP5 tests. Good agreement between the test data and simulations suggests that the proposed model can provide sufficiently accurate prediction of both local and large scale phenomena induced by steam injection into the pool.

The effects of spacing to diameter ratio on mixing characteristics of circular and elliptical twin jets

Twin jets are encountered in many engineering and industrial applications, such as aircraft propulsion systems and combustors. Twin jets create a flow field that is more complex than a single jet due to its interaction with the individual jets. This paper investigates the effects of spacing to diameter ( S/ D e) ratio and orientation on the mixing properties of circular and elliptical twin jets at four different S/ D e ratios of 1.25, 1.50, 1.75, and 2.0, respectively. The numerical simulations of twin jets are carried out with a jet Mach number of 0.8 using the Shear Stress Transport ( SST) K- ω turbulence model. The results show that near the orifice exit, the twin jets are issuing into ambient conditions separately and resemble a free jet, leading to a potential core length independent of S/ D e. The merging and combined point locations change linearly from the exit with an increasing S/ D e ratio. The decay rate is higher for Twin Ellipse Minor than those in Twin Circle and Twin Ellipse Major, verified by a shorter converging region. In addition, near the jet exit, the spread rate is higher for Twin Ellipse Minor, which is consistent with the closer merging point location. The jet mixing is superior for twin minor elliptical configuration compared to twin circle and twin major elliptical jets at all S/ D e ratios.

Multiple Abyssal Jets Flowing Into the Vema Deep, Romanche Fracture Zone

AbstractStrong acceleration of abyssal flows in narrow deep‐water channels and fracture zones is a key feature of bottom circulation in the Atlantic Ocean. In the Equatorial Atlantic, these bottom currents transport Antarctic Bottom Water (AABW) over the Mid‐Atlantic Ridge from west to east. The main pathway for Antarctic waters in this region is the Romanche Fracture Zone. The deepest point of this fracture zone is the Vema Deep; its maximum depth based on the published data is 7,856 m. This deep basin is filled by waters of Antarctic origin overflowing a sill in a narrow channel. During the expedition on the R/V Akademik Ioffe (August 2022), we revealed a strong flow in the middle part of the Romanche Fracture Zone and collected new data on thermohaline and kinematic structures of this gravity current. Our survey is the first observational evidence of the intense flow into the Vema Deep. At the sill, the flow splits into branches flowing through three distinct channels of intricate configuration located in the southern transform valley of the fracture zone. The northern channel is proved to be the main pathway of the coldest and densest bottom waters to the Vema Deep. We also found that vertical structure of the flow is presented by two individual jets, namely the deep and bottom jets. The total transport of AABW through the Romanche Fracture Zone at this location was estimated at 1.40 Sv; the velocities exceeding 10 cm/s were found at depths greater than 5,000 m.

Study on Collision Process of Opposing Unsteady Supersonic Jets and Shock Waves

Double pulsed-laser-ablation is a promising method to prepare nanoparticle composites. The backward movement of the plume after the collision with counter-propagating shock wave has been observed in experiments. In the present study, collision dynamics of the oppositely injected Si and Ge jets into a He background gas was numerically calculated as a simulation for double pulsed-laser-ablation. The experimentally observed backward movement was reproduced. The effect of distance between two jet exits on the distance of backward movement of the jet, BL, after the collision with the counter-propagating shock front was calculated to discuss the collision dynamics and to optimize the target distance for the experiment. We found that BL does not decrease monotonically with increasing distance between two jet exits, but has a maximum value at a certain distance. This behavior is discussed by calculating the expansion dynamics of an individual jet. Shock wave grows with time at the initial stage of the jet expansion and then attenuates; the density just behind the shock front for individual jet has a maximum value at a certain time and position. BL has a maximum value when the densities just behind the shock fronts for the individual jets have maximum values. This result is important for designing the appropriate distance between the two jet exits, i.e., the distance between the targets of double pulsed-laser-ablation.

Electrothermal System Design and Evaluation of Low EMI and Thermally Balanced 150 kW T-Type Traction Inverter

Power electronics switching devices utilized in traction, propulsion, and power generation applications require advanced thermal management systems and extensive electromagnetic interference filtering components. The traditional indirect cooling methods exhibit limited ability to target switching location hotspots, causing limited cooling capabilities and thermal imbalance. Additionally, they rely on metallic structures directly integrated with module base plates, allowing for an accentuation of common-mode noise. These effects present themselves concurrently, creating reliability concerns while requiring further noise filtering. This work demonstrates the integration of a nonmetallic jet impingement cooler for direct base plate thermal management of a 150 kW silicon-carbide inverter. The use of nonmetallic structures manufactured through additive techniques limits low-induction capacitance pathways by 99%, leading to a 25 dB reduction in common-mode noise. Impingement jets focused on module hotspots reduce maximum device temperatures and increase thermal uniformity. Finally, by attaching individual jet coolers to each power module, hydraulic circuit networks are used to demonstrate thermal balancing between power devices for optimal current sharing.

Investigation into shock-to-shock interactions induced by flash boiling and the impact on spray behaviors

Through recent numerical studies, the shock-to-shock interactions between flash-boiling jets are believed to be the reason for multi-jet spray collapse in gasoline direct injection (GDI) engines. But this sort of interaction was not well understood through the experimental investigation. In the present study, a two-hole GDI injector was used to examine this process via optical diagnostics and CFD simulations. With the increase in superheat level (Rp), the shock waves (primary cells) in individual jets became observable. Further increase in Rp could cause shock-to-shock interactions, and a secondary cell could be formulated between two primary cells. The different intensity of shock-to-shock interactions would result in different jet-to-jet interaction behaviors. In the moderate interaction region, the secondary jet appeared inside and downstream of the secondary cell, but the sprays did not collapse. In the highly interaction region, both the secondary jet and spray collapse could be observed, where the secondary jet would laterally develop perpendicular with the plane of the two jets. The detailed numerical results showed that the secondary cell was small in the moderate interaction region, but became much larger in the highly interaction region. The occurrence of secondary cell directed the fuel from primary cells into the secondary cell, contributing to the generation of secondary jet. After flowing out of the secondary cell, the incipient secondary jet could subsequently entrain the nearby low-velocity fuel. Further, the strong shock-to-shock interactions would alter the shape of primary cells, reducing the transverse velocity component of jets and promoting collapse. Based on the experimental and numerical results, the existence of shock-to-shock interactions and its important role in jet-to-jet interactions and spray collapse were fully illustrated, and this understanding would be of help in nozzle optimization.

A conical assembly of six plasma jets for biomedical applications

A conical assembly of six plasma jets arranged in a rectangular pattern for biomedical applications is presented. The conical configuration increases the separation distance between individual tubes within the assembly that reduces interference between individual plasma jets and enables the jets to converge at the output, facilitating more uniform treatment as opposed to plasma jet arrays operated in parallel. Electrical and optical diagnostics of the plasma discharges and measurements of H2O2 and NO2− production in de-ionized water are used to characterize the potential suitability of the device for biomedical applications. Particularly, it was found that the efficiency in H2O2 (an important bacterial disinfection agent) production by the conical assembly of six plasma jets was more than nine-fold higher compared to its single plasma jet counterpart and that this could be achieved at a biocompatible temperature of below 300 K. Therefore, the device may find use in biomedical applications, particularly where larger area treatments are required such as for certain wounds and cancer tumors that can span areas of tens of cm2.

Visualization of a Small Jet Synthetic Using a Particle Image Velocimetry and Background-Oriented Schlieren Techniques

This work reports the results of experimental investigations carried out on a submerged synthetic jet obtained through the use of a headset speaker piloted with an appropriate sinusoidal signal at a frequency of 380 Hz. The study begins with the construction of a device that, exploiting the well-known transport properties of impacting jets, was able to improve local ventilation and the removal of excess moisture, due to the natural transpiration of human skin in people forced to assume the same position for prolonged periods such as professional drivers; bedridden patients; etc… Subjects are substantially forced to have parts of their own body in contact with fabrics and coverings that hinder the normal conditions of skin transpiration. The experimental activity was first based on the study of the structure of the synthetic jets, then moving on to the creation of a sponge mat equipped with 80 individual jets. On this sponge mat, semi-empirical tests were carried out in order to remove moisture from a fabric soaked in distilled water. The experimental investigations were first carried out using the PIV technique, and, subsequently, the synthetic jet was visualized using the Background-Oriented Schlieren (BOS) technique which allowed to test the presence of the jets, installed directly on the mattress, in a relatively simple and fast way, requiring a very simplified set-up.