Jet Wind Research Articles

Effect of Combination Yaw Angle Variation and Base Bleeding for Tractor-Trailer Drag Reduction through Experimental Investigation and CFD

This study focuses on the effect of variations in yaw angle and base bleeding configuration on the reduction of tractor-trailer drag. Detailed experimental and CFD investigations are introduced. Crosswind is used to simulate the yawed flow conditions. Three bleeding hole settings are arranged in the tractor base area. Experiments and CFD are done using 1:32 scale model, after validating the results of the CFD extended to a full-scale model. In the CFD investigation, the structure and rotation of the flow around the tractor-trailer and the gap area are examined. Experimental investigations was Carried out in an open jet wind tunnel. The results showed that when the yaw angle is greater than 3 a drag reduction is clearly observed. At the yaw angle of 12 ° maximum drag reduction occurs in the form of drag coefficient is 19%, 21% and 23% for bleeding coefficient of 0.04, 0.05 and 0.06. Through the results of CFD predictions, the effects of bleed increase entrainment flow in the gap and reduce the wake area on the leeward side of the trailer and consequently produce a significant reduction in drag. This result is caused by a large flow separation zone that forms along the underside of the trailer when there is no bleeding which increases vehicle drag. The appropriate bleeding area of the tractor base is an alternative that allows in reducing the drag in the tractor- trailer gap.

A Companion Star Launching Jets in the Wind Acceleration Zone of a Giant Star

By conducting three-dimensional hydrodynamical simulations we find that jets that a main-sequence companion launches as it orbits inside the wind acceleration zone of an asymptotic giant branch star can efficiently remove mass from that zone. We assume that during the intensive wind phase a large fraction of the gas in the acceleration zone does not reach the escape velocity. Therefore, in the numerical simulations we blow the wind with a velocity just below the escape velocity. We assume that a main-sequence companion accretes mass from the slow wind via an accretion disk, and launches two opposite jets perpendicular to the equatorial plane. This novel flow interaction shows that, by launching jets, a companion outside a giant star, but close enough to be in the acceleration zone of a slow intensive wind, can enhance the mass-loss rate from the giant star by ejecting some gas that would otherwise fall back onto the giant star. The jets are bent inside the wind acceleration zone and eject mass in a belt on the two sides of the equatorial plane. The jet–wind interaction contains instabilities that mix the shocked jets' gas with the wind, leading to energy transfer from the jets to the wind. Our new simulations add to the rich variety of jet-induced outflow morphologies from evolved stars.

Trailing edge bluntness noise reduction using porous treatments

This paper provides an experimental investigation of the noise generated from a blunt flat plate and the possibility of the control of noise at source using porous trailing edges. The noise generation characteristics have been examined using a flat plate equipped with surface pressure transducers and far-field microphones and was performed in an anechoic open jet wind tunnel. Two types of porous materials with different porosities and permeability constants were tested. Simultaneous near-field and far-field noise measurements, as well as the boundary layer and wake flow measurements, have been carried out to better understand the effects of the porous treatment to the flow-field and the noise generation mechanism of the plate. Results have shown that the use of porous trailing edges can generally lead to the effective suppression of both the tonal noise, due to the vortex shedding from the blunt trailing edge and also the broadband noise of the plate. The level of the noise reduction was also found to be dependent on the porosity and permeability of the porous materials. The directivity patterns of the radiated noise have shown significant noise reduction at the vortex shedding frequencies. The flow measurement results have shown that the use of porous trailing edges leads to the reduction of flow acceleration over the blunt edges, and subsequently the delay and weakening of the vortex shedding. The results presented in this paper provide an impetus for further experimental and numerical studies on the use of porous treatments for the suppression of aerodynamically generated noise at source.

Vortex Shedding Noise from Finite, Wall-Mounted, Circular Cylinders Modified with Porous Material

The aerodynamic noise generated by a circular cylinder in a crossflow is a classical problem in aeroacoustics, which can be found in various practical applications, such as parts of the landing gear of airplanes, train pantographs, and antennas of vehicles. The noise is especially disturbing because it contains strong tonal contributions due to the regular vortex shedding at the cylinder. If the cylinders are not two-dimensional, but finite and wall-mounted at one end and free at the other, additional flow phenomena occur at both the tip and the wall junction, which can lead to additional noise contributions. One method to reduce the aerodynamic noise from such cylinders is to cover them with a flow-permeable, porous material. The present paper describes an experimental study on the effect of porous covers on the reduction of noise generated by wall-mounted, finite, circular cylinders. Thereby, special focus was put on the identification of both the optimum position and the optimum extent of the porous cover regarding a maximum noise reduction. The experiments included both measurements of the far field noise as well as flow measurements in the wake of the cylinders. They were conducted in an aeroacoustic open jet wind tunnel at subsonic flow speeds. It was found that a placement of porous material at the wall end is more efficient in reducing Kármán vortex shedding noise than a placement of porous material at the free end.

Experimental characterization of the interaction zone between counter-propagating Taylor Sedov blast waves

Astronomical observations reveal that the interaction between shock waves and/or blast waves with astrophysical objects (molecular clouds, stars, jet winds, etc.) is a common process which leads to a more intricate structure of the interstellar medium. In particular, when two isolated massive stars are relatively close and explode, the resulting Supernovae Remnants (SNRs) can interact. The impact zone presents fascinating complex hydrodynamic physics which depends on the age of the SNRs, their relative evolution stage, and the distance between the two stars. In this Letter, we investigate experimentally the interaction region (IR) formed when two blast waves (BWs) collide during their Taylor-Sedov expansion phase. The two BWs are produced by the laser irradiation (1 ns, ∼500 J) of 300 μm diameter carbon rods and propagate in different gases (Ar and N2) at different pressures. The physical parameters, such as the density and temperature of the IR, are measured for the first time using a set of optical diagnostics (interferometry, schlieren, time-resolved optical spectroscopy, etc.). This allows us to determine precisely the thermodynamic conditions of the IR. A compression ratio of r ∼ 1.75 is found and a 17–20% increase in temperature is measured compared to the shell of a single blast wave. Moreover, we observe the generation of vorticity, inducing strong electron density gradients, in the IR at long periods after the interaction. This could in principle generate magnetic fields through the Biermann Battery effect.

Study on the Atomization and Dust‐Reduction Performance of a New Type of External Pneumatic Vortex Fog Curtain Dust Removal Device in Fully Mechanized Excavation Face

To solve the problem of dust pollution in the heading face, a new type of external pneumatic vortex fog curtain dust removal device suitable for a fully mechanized excavation face is designed in this paper. Firstly, dust migration laws at different times are simulated and analyzed by COMSOL software, and the functional relationship of dust concentration distribution above 50 mg/m3 at different heights and different wind speed is derived. Aiming at the dust migration laws of the heading face, a new dust removal device was proposed, and the atomization performance of the new type of external pneumatic vortex fog curtain dust removal device under different jet wind speed, different atomization pressure, and different nozzle working angle is explored through atomization performance experiment. It is found that when jet wind speed is 30 m/s, atomization pressure is 4 MPa, and nozzle working angle is 75°, the atomization performance of the new type of external pneumatic vortex fog curtain dust removal device is the best. Through the simulation of COMSOL software, the influence of air volume on the new type of external pneumatic vortex fog curtain dust removal device is analyzed. It is found that the new type of external pneumatic vortex fog curtain dust removal device is relatively stable when the air volume at the pressure outlet is less than 400 m3/min. The dust‐reduction efficiency of the new type of external pneumatic vortex fog curtain dust removal device was investigated through the dust‐reduction experiment, and it is found that the new type of external pneumatic vortex fog curtain dust removal device had better dust removal performance under the condition that the ventilation conditions did not interfere with the integrity of the vortex fog curtain.

Analysis of cross axis wind turbine blades designed and manufactured by FDM based additive manufacturing

Additive manufacturing is emerging as a preferred approach to manufacture complex three dimensional components easily within a short span of time. In this study, cross axis wind turbine blades and its components are produced using fusion deposition modeling using Acrylonitrile Butadiene Styrene (ABS) material. The 3D CAD models are converted into .STL file which are processed further in “Slicer” freeware software. This convert the model into series of thin layers and creates G-code file which acts as an input to automated 3D printing machine to lay layers of loaded thermoplastic material successively to build the model from series of cross sections. The components produced by additive manufacturing is assembled and the obtained cross axis wind turbine (CAWT) is investigated using an open jet wind tunnel for wind velocities varying from 4 m/s to 10 m/s. The dimensionless performance parameters i.e., coefficient of power (Cp) and tip speed ratio (λ) are plotted. In general, the Cp value of CAWT increases gradually and reaches the maximum value around λ = 1.20. A maximum Cp value of 0.02385 is observed for wind velocity Vα = 10 m/s. Thus, the 3D printed components by additive manufacturing can be used to produce small wind turbines.

Dipole-wind interactions under gap wind jet conditions in the Gulf of Tehuantepec, Mexico: A surface drifter and satellite database analysis.

Gap wind jets (Tehuano winds) trigger supersquirts of colder water and mesoscale asymmetric dipoles in the Gulf of Tehuantepec (GT). However, the effects of successive gap wind jets on dipoles and their effects inside eddies have not yet been studied. Based on the wind fields, geostrophic currents, and surface drifter dispersion, this research documented three dipoles triggered and modified by Tehuano winds. Once a dipole develops, successive gap wind jets strengthen the vortices, and the anticyclonic eddy migrates southwestward while the cyclonic eddy is maintained on the east side of the GT. During the wind relaxation stage, the cyclonic eddy may propagate westward, but due to the subsequent re-intensification of the Tehuano winds, the vortex could break down, as was suggested by surface drifter dispersion pattern and geostrophic field data. The effect of the Tehuano winds was evaluating via eddy-Ekman pumping. Under Tehuano wind conditions, Ekman downwelling (upwelling) inside the anticyclonic (cyclonic) eddies may reach ~ -2.0 (0.5) m d-1 and decrease as the wind weakens. In the absence of Tehuano winds, Ekman downwelling inside the anticyclonic eddy was ~ 0.1 (-0.1) m d-1. The asymmetry of downwelling and upwelling inside eddies during Tehuano wind events may be associated with Tehuano wind forcing.

Data supporting manuscript "Generation and intensification of mesoscale anticyclones by orographic wind jets: the case of Ierapetra Eddies forced by the Etesians" submitted to JGR Oceans

Data supporting manuscript "Generation and intensification of mesoscale anticyclones by orographic wind jets: the case of Ierapetra Eddies forced by the Etesians" submitted to JGR Oceans

A Fresh Look at Narrow-angle Tail Radio Galaxy Dynamics, Evolution, and Emissions

Abstract We present a 3D magnetohydrodynamic study of narrow-angle tail (NAT) radio galaxy (RG) dynamics, including passive cosmic ray electrons. We follow the evolution of a bipolar-jet RG in a persistent crosswind through hundreds of Myr. We confirm traditional jet-bending models, while noting that our NAT exhibits a transitional morphology reminiscent of wide-angle radio tails. Once deflected, jets remain internally stable, but are intermittently disrupted by external disturbances induced by the NAT dynamics itself. The disruptions enhance jet and tail magnetic fields. Disrupted jet plasma is heterogeneously mixed with denser wind plasma, yielding patchy, filamentary tails that grow longer at a rate exceeding the wind speed. Such fast tail extension could, for example, allow NAT tails to overtake extraneous intracluster medium (ICM) features, such as shocks and shear layers downwind of where the tails first form. Those events, in turn, could generate enhanced radio emissions within the ICM features themselves that do not follow the geometrical extension of the tails past the encounter. Analysis of synthetic radio observations reveals an extended time period once the NAT has developed in which it displays a nearly steady-state morphology with integrated fluxes that are roughly constant, along with a self-similar, curved integrated spectrum. In an appendix, we outline a simple analytic jet trajectory formalism with one adjustable parameter, using it to illustrate explicit trajectories that extend the classic bending model to arbitrary jet–wind orientations.

Study of the aerodynamic parameters of the installation, generating wind flow in open space

The article is devoted to the study of the aerodynamic parameters of the installation, causing wind flow in open space. In the open space, a model of an aerodynamic installation which creates an uneven wind flow rate is presented. To determine the speed at each distance using an aerodynamic model, creating a jet wind, an experiment was conducted. The results of experimental studies to determine the speed when changing the flow rate and rotation number at a distance from 10 cm to 130 cm from the propeller model are given. Experimentally found to reduce the speed in the stream, distributed from the propeller, when y = + 10 cm, y=-10 cm, with increasing distance, and the axial velocity in the stream, distributed from the propeller.

Seasonality and interannual variability of the Sri Lanka dome

Located in the southwest Bay of Bengal, the Sri Lanka Dome (SLD) is an upwelling tropical thermal dome that forms in a region of positive wind stress curl within the Southwest Monsoon Current (SMC) system. Here, we quantify variability in the SLD's sea surface slope, area, amplitude, and position using a 22-year record of absolute dynamic topography. We observe a seasonal cycle in the evolution of the SLD and its relationship to wind stress curl. The SLD typically forms in early June in a region of positive wind stress curl associated with the wind jet off Sri Lanka. For the first two months after formation, the magnitude of the SLD's sea surface slope strongly correlates with the strength of the wind stress curl. Later in the southwest monsoon, the SLD's position shifts northward moving out of the region of strong wind stress curl, before dissipating in typically September. The amplitude and area of the SLD vary together, and both are linked to the strength of the SMC on weekly timescales. Decadal variability in both the SLD and wind stress curl is reflected in the Dipole Mode Index, which reflects an integrated measure of regional forcing. These results suggest alignment between the SMC and the region of wind stress curl may play a pivotal role in controlling the strength of the SLD on seasonal and interannual timescales.

An Overview of Low‐Level Jet Winds and Corresponding Mixed Layer Depths During PECAN

AbstractThirty southerly low‐level jet (LLJ) events were observed during the Plains Elevated Convection at Night (PECAN) field campaign in the Great Plains region of the United States during summer 2015. Here we present Doppler lidar wind data from three PECAN instrumentation sites to explore characteristics of LLJs and the boundary layer as well as some of the heterogeneities possible within the wind field of a LLJ. Southerly LLJs were observed on 66% of nights at the southwestern site (Greensburg, KS) but only 56% and 53% of nights at the eastern and northern sites, respectively (Hesston and Ellis, KS). The northernmost site had a relative abundance of weaker jets or nonjet conditions due to fronts or convective systems that only affected part of the observation domain. Plotting mean wind fields of each LLJ type reveals that the strongest LLJs tend to develop under very similar conditions but begin to show variability in wind profile evolution after several hours. A robust mixed layer height retrieval algorithm is used to investigate the interplay between the jets and the turbulent convective boundary layer, showing that stronger LLJs are preceded by deeper afternoon mixed layers and often have a later decoupling of mixing between the upper convective mixed layer and the near‐surface layer. Only the strongest LLJs generated a shallow mixing layer overnight. Comparing jet strength and direction to pristine nocturnal convection initiation shows that the strongest southerly LLJs yielded the most pristine nocturnal convection initiation events per night, and the pristine nocturnal convection initiation occurred farther north.

Low‐Level and Surface Wind Jets Near Sea Ice Edge in the Beaufort Sea in Late Autumn

AbstractLow‐level wind jets (LLJs) and strong surface winds are frequently observed near the sea ice edge in the presence of strong thermal contrast between open water and sea ice. Two LLJ cases near the sea ice edge in the Beaufort Sea are examined using dropsonde observations made from Seasonal Ice Zone Reconnaissance Survey flights. Ensembles of Polar Weather Research and Forecast simulations with and without sea ice demonstrate the contribution of the surface thermal contrast to the boundary layer structure, the LLJ, and surface ice edge jets. Because the surface temperature contrast only influences the lower most hundreds of meters in the atmospheric boundary layer, its contribution to the temperature gradient and wind speed at the level of the LLJ is limited. The sea ice does strengthen the LLJ by extending the LLJ northward over sea ice and increasing the maximum LLJ wind speeds by up to 13% and as much as 29% further north at a lower altitude. However, the primary reason for the observed strong winds in these two cases are the synoptic interactions between anticyclones and approaching cyclones. The effect of the surface thermal contrast on surface winds is controlled by a separate mechanism. The cold and stable boundary layer over sea ice prevents the momentum transport from the LLJ to the surface. This leads to weaker surface winds over sea ice and confines the strong surface winds close to the sea ice edge. This mechanism contributes to the frequent occurrence of the surface “ice edge jets.”

Magnetar as Central Engine of Gamma-Ray Bursts: Central Engine–Jet Connection, Wind–Jet Energy Partition, and Origin of Some Ultra-long Bursts

Gamma-ray burst (GRB) central engines and jet production mechanisms are still open questions. Assuming that the shallow decay segments of canonical X-ray afterglow lightcurves of {\em Swift} GRBs are attributed to the magnetic dipole (MD) radiations of newly-born magnetars, we derive the parameters of the magnetars and explore their possible relations to jet and MD wind emission. We show that the magnetar initial spin period ($P_0$) are tightly correlated with the jet energy ($E_{\rm jet}$), which is almost proportional to the wind energy ($E_{\rm wind}$). Our least square fits yield $P_0\propto E^{-0.36\pm 0.03}_{\rm jet}$ and $E_{\rm wind}\propto E^{0.91\pm 0.07}_{\rm jet}$. These relations may imply that a magnetar with faster rotating speed can power a more energetic GRB, and energy partition between the jet and wind may be quasi-universal. Although the $P_0-E_{\rm jet}$ relation is driven by a few sub-energetic GRBs in our sample, our Monte Carlo simulation analysis shows that sample selection biases from instrumental flux limits and contaminations of the bright jet afterglows cannot make this correlation. Within this jet-wind paradigm, we propose that GRB 101225A-like ultra-long GRBs, whose prompt gamma-ray/X-ray lightcurves are featured as a long-lasting plateau with a sharp drop, may be the orphan MD wind emission being due to misalignment of their jet axis to the light of sight. Brief discussion on the orphan MD wind emission and its association with the gravitational wave radiation of newly-born magnetars is presented.

Gravity Wave Ducting Observed in the Mesosphere Over Jicamarca, Peru

AbstractShort‐period gravity waves are ubiquitous in the mesosphere, but the vertical structures of their perturbations are difficult to observe. The Jicamarca 50‐MHz very high frequency radar allows observations of winds and turbulent scatter with high temporal and vertical resolution. We present a case of a quasi‐monochromatic gravity wave with period 520 (±40) s that is likely ducted below a southward wind jet between 68 and 74 km. Above this layer of evanescence, a northward wind enables it to emerge into a more stable layer, where it is refracted to a short vertical wavelength of 2.2 (±0.2) km; data show evidence of weak nonlinearity, and possible overturning or partial reflection from higher altitudes, above the observable region, in the form of a standing wave structure in vertical velocity at approximately 75 km. Based on the dispersion relation, and with help of a two‐dimensional model, we determine that most likely the wave is propagating northward and is being ducted below and tunneling through the regions of evanescence created by the wind flow and typical mesospheric thermal structure. This is the first time that such an event has been identified in the Jicamarca mesospheric echoes, and it is distinct from Kelvin‐Helmholtz billows also commonly seen with this sensitive radar—instead apparently revealing tunneling of the gravity wave through ambient winds.

Self Noise Reduction and Aerodynamics of Airfoils with Porous Trailing Edges

The application of open-porous materials is a possible method to effectively reduce the aerodynamic noise of an airfoil. However, the porous consistency may have a negative effect on the aerodynamic performance of the airfoil, since very often the lift is decreased while the drag increases. In a recent investigation, the generation of trailing edge noise of a set of airfoil models made from different porous materials was examined experimentally. The materials were characterized mainly by their airflow resistivity. Besides the material, the chordwise extent of the porous material was varied, which was done by covering the front part of the porous airfoil with a thin, impermeable adhesive foil. Acoustic measurements were performed in an open jet wind tunnel using microphone array technology, while the aerodynamic performance was measured simultaneously using a six-component balance. In general, both the airflow resistivity and the extent of the porous material have an influence on the trailing edge noise. However, if a suitable material is chosen, the results show that a noticeable reduction of trailing edge noise is possible even with only a small chordwise extent of the porous material.

A Climatological Analysis of the Benguela Coastal Low‐Level Jet

AbstractThe Benguela coastal low‐level jet (CLLJ) is characterized by intense winds that occur around 400 m above sea level, within or at the top of the marine atmospheric boundary layer. The semipermanent St. Helen high‐pressure system, over the South Atlantic Ocean, and the inland thermal low‐pressure system, over the Namib Desert, are the synoptic forcing behind the Benguela CLLJ. This coastal jet is an important mesoscale feature in the Namibia and Angola coastal areas, since it is present virtually all year round, with a marked seasonal cycle. This study investigates the climatology of the frequency and the intensity of the Benguela CLLJ and its relationship with synoptic and local forcing's, using high‐resolution modeling. An uncoupled ROM (REMO‐OASIS‐MPIOM) hindcast simulation, with 25‐km horizontal resolution, for the period 1980–2014, is used to analyze the features of the Benguela CLLJ. It is shown that Benguela CLLJ is characterized by two local maxima of frequency of occurrence at around 26°S and 17.5°S. During austral summer, the jet has a frequency of occurrence of about 60% and it is in its southern core. During autumn and winter, the frequency of occurrence decreases to nearly half and migrates equatorward. During spring, the jet has a frequency of occurrence of 45% and is found at the northern core. The jet wind speed is higher in the south core but is found at higher altitudes in the north core. The seasonal cycle of horizontal momentum budget defines the seasonality of Benguela CLLJ frequency of occurrence.

Design and fabrication of the subsonic wind tunnel for aeroacoustic measurements

This paper presents the design and analysis of a free jet, blow down subsonic wind tunnel for aeroacoustic measurements. The wind tunnel is made from the artificial fibre which is optimised for achieving subsonic, i.e. 0.3 ≤ M ≤ 0.8 steady flow (low turbulence). The flow control techniques such as orifice holes were distributed uniformly over the perforated plates of diameter 302 and 444 mm positioned at 30% and 45% respectively, to reduce the turbulence flow. The aerodynamic performances of the Free Jet Wind Tunnel (FJWT) have been studied at both incompressible (M < 0.3) and compressible (0.3 ≤ M ≤ 0.8) conditions of about 75 m/s, 1.3 bar, 2.25 bar and 4.5 bar. From the results, it is evident that the uncertainty in the wind tunnel is low compared with the traditional wind tunnel. Further, the acoustic measurements uncertainty is obviously lesser than other configurations.

Wind velocity and wind curl variability over the Black Sea from QuikScat and ASCAT satellite measurements

Measurements of QuikScat for 2000–2009 and ASCAT scatterometers for 2009–2016 are used to describe the variability of the Black Sea wind velocity and wind curl. High-resolution (12.5 km) scatterometry data provide a possibility to investigate several small-scale features (“hot points”) of the wind field in the basin related to the topographic effects. They include: the gap winds near the Bosphorus, the Kerch Strait, and Tuapse; tip jets at the south and west of the Crimean peninsula, several capes of the Anatolian coast; the Kolkheti valley winds; wind shadow zones at the eastern Turkey coast and the western Crimean coast. Driving factors and directional variability of wind in these “hot points” is discussed.QuikScat and ASCAT data are used to describe seasonal and interannual variability of wind characteristics in 2000–2016. Comparison with in-situ data shows that QuikScat noticeably overestimates wind magnitude during low winds conditions (<2 m/s). ASCAT winds are generally lower than QuikScat, but the ASCAT wind curl is higher. The amount of low winds values (<2 m/s) in the ASCAT data is 6% of the total data, and it is 1% in the QuikScat data. Overestimation of low winds decreases wind gradients near the wind shadows, which is the most possible reason of the underestimation of the wind curl in the QuikScat dataset.Wind curl has a different sign and a completely different interannual variability in the western and eastern parts of the sea. Near the eastern coast of the basin, high-resolution satellite measurements reveal three powerful small-scales maximums of cyclonic vorticity. These maximums are related to the wind jets flowing around topographic obstacles in the vicinity of the Kerch Strait, in the mountain gap near Tuapse, and from the Kolkheti valley. They are observed throughout the whole year, but are largest in winter. The contribution of these maximums to the overall cyclonic vorticity is essential (30% in the QuikScat data and 50% in the ASCAT data). In the western part of the basin, the wind curl is negative (anticyclonic) on average, with the highest anticyclonic curl observed in summer. Winds are decreasing in 2000–2016 in agreement with the data on the 20 century. At the same time the basin-average wind curl rises due to its increase in the eastern Black Sea. We speculate that these trends are associated with the displacement of the Siberian Anticyclone to the west. The related rise of pressure over the eastern Europe correlates significantly with the wind curl variability on interannual time scales.