Doppler Velocimetry Technique Research Articles

Impact of blade shape on the aerodynamic performance and turbulent jet dynamics produced by a ducted rotor

A ducted rotor system was used to produce turbulent jets with a Reynolds number up to 5.97 × 105 and Mach number of 0.222 based on mean streamwise velocity. Three rotors with a diameter of 11.8 cm were manufactured and tested inside a duct with a 1 mm tip clearance at a speed up to 30 000 revolutions per minute (rpm). All rotor blades contain the same aspect ratio of 2.2, a National Advisory Committee for Aeronautics 2410 airfoil, and ideal pitch distribution. However, three different blade planform shapes were used including a rectangular shape with constant chord, trapezoidal shape with a taper ratio of 0.5, and elliptical shape where the trailing edge of the blade is expressed with an elliptical function. The rotor thrust and electric power were measured, and the thrust coefficient and figure of merit was computed. The flow-field produced by the ducted rotors was measured in the near-field using laser Doppler velocimetry techniques. The inflow velocity approximately 3 mm upstream of the rotor blade leading edge was acquired and its significance on blade aerodynamics and performance is analyzed. Time-averaged contours of cross-stream vorticity reveal intense hub and blade tip vortex structures, which are impacted by the shape of the blade, particularly in the blade tip region. Tip vorticity as well as streamwise turbulence intensity and turbulent kinetic energy in this region were mitigated for the rotors with trapezoidal and elliptical blades. However, the turbulent structure of the jet produced by all three rotor blade shapes showed similarity at a mere 2.8 rotor diameters downstream of the rotor. This finding emphasizes the importance of blade design on the near-field dynamics of ducted rotor flows for aircraft propulsion.

Mock-up conception for experimentally investigate the creep phenomenon caused by the fluid–structure interaction in a rod bundle

Pressurized water reactors (PWRs) are employed worldwide and continue to expand in capacity. They require thorough investigation, particularly concerning their safety and operational efficiency. To ensure these factors, comprehensive research into their various components and an understanding of the diverse phenomena they experience within a PWR are imperative. These phenomena can be of mechanical, thermal, hydraulic, or neutronic nature. Among these components, fuel assemblies (FAs) hold a main role in PWRs. The intricate interplay of these physical factors results in the modification of FAs geometry, specifically permanent elongation and lateral deformations referred to as irradiation creep. The earliest reported occurrence of these deformations dates back to 1994 in Ringhals reactors, where various FAs exhibited distinct deformations (Andersson et al., 2005). Given that these phenomena occur over a time span of months to years in metallic materials, conducting investigations within the confines of a typical laboratory observation period becomes impractical. Consequently, this project proposes an alternative experimental methodology to overcome this challenge, thus gaining a deeper understanding of the fluency phenomenology in FAs behavior. This methodology consists on the design of a reduced-scale test section, capable of replicating the fluid–structure interaction (FSI) responsible for creep, the creation of spacer grids through 3D printing technology, and selection of the appropriate material for the fuel rods (FRs), with an emphasis on macroscopic coupling effects, rather than focusing into the micro-structural response of the material. To experimentally observe the deformation on the FAs, cameras were used to capture images through the time during the test, to catch the displacement of the FRs. The first results showed the mock-up was able to reproduce the FSI causing the creep on the FAs, it was possible to capture the displacement evolution along time, and to observe different types of deformation, thus, it helps to understand the phenomenon. Further tests and investigations using laser doppler velocimetry (LDV) technique to analyze the flow will be held, to a better comprehension of these burden.

Buoyant miscible viscoplastic displacements in vertical pipes: Flow regimes and their characterizations

We experimentally study miscible displacement flows of a light Newtonian fluid by a heavy viscoplastic fluid, in a vertical pipe with a large aspect ratio (δ−1≫1). We use camera imaging, laser-induced fluorescence, and ultrasound Doppler velocimetry techniques, to capture and process data. Four dimensionless parameters, namely, the Reynolds (Re), Bingham (B), viscosity ratio (M), and densimetric Froude (Fr) numbers (or their combinations), mainly govern the flow dynamics. We identify and characterize three distinct flow regimes, including plug, separation, and mixing regimes, while we describe each regime's dynamics in detail, particularly in terms of the velocity and concentration fields as well as the displacement front velocity. In addition, we analyze the plug regime concerning the residual wall layers, the separation regime in terms of the separation dynamics, spatiotemporal separation zone, and viscoplastic layer thinning, and the mixing regime regarding the mixing index and macroscopic diffusion. Finally, we develop a simplified model to help delineate the flow regime classification, in the plane of Re/Fr2 and M.

Uncovering the fracture behavior of metallic cylindrical shells under internal explosive loadings via careful design of densely-arranged multi-point photon Doppler velocimetry measurements

While the expanding process of cylindrical shells under internal explosive loadings is fundamental and ubiquitous in engineering applications, the comprehensive understanding of the underlying mechanism is still a challenge due to the limitation of the spatial resolution on the current diagnostic techniques. To address this issue, an improved densely-arranged multi-point photon Doppler velocimetry (DMPDV) technique with enough spatial resolution to capture the local dynamical evolution was carefully designed. The DMPDV technique was then applied to investigate the expanding behavior of an explosively driven 304 L stainless steel cylindrical shell. As a step beyond the coarse understanding of the overall dynamical response, the expanding process can then be demonstrated comprehensively with more exact concentrations on one fragment. By the combination of DMPDV and high-speed photography, we uncovered the evolution of the expanding process which can be divided into three stages: (1) In the beginning, due to the symmetries of the specimen and the loading, the cylinder expands uniformly and all the velocity-time curves at different hoop positions are coincide with each other. (2) after the emergence of cracks at the outer surface of the cylinder, the velocity-time curves start to separate from each other and are regularly arranged according to their test positions. (3) following the penetration of the crack through the thickness of the cylinder, there is a reverse in the velocity-time curves and the fragments begin to rotate, the rotation angle can be estimated using the velocity difference. The hidden mechanism is then revealed with the help of unloading wave theory and rigid body dynamics. Here the second stage is dominated by unloading wave while the last stage is controlled by the denotation products. These experimental results provide deep insight into the detailed fracture behavior of expanding cylindrical shell and are further validated by the Mott wave models as well as numerical simulations, respectively.

Effect of blade aspect ratio on the performance tradeoff between figure of merit and bending-torsion dynamics of wind turbines with synthetic jets

In this experimental study, two three-bladed rotors with a blade aspect ratio of 7.79 and 9.74 representing a 25% increase were tested. Each blade contains an S809 airfoil with zero pre-built twist and 20 high-performance synthetic jet actuators distributed along the span. The rotor was tested at four rotor speeds, Ω of 250, 500, 750, and 1,000 revolutions per minute (RPM) and three collective blade pitch angles, θc of 2, 5, and 8 degrees. Rotor thrust was measured using a high-capacity load cell, and blade bending and torsion was measured at four equally spaced radial locations on the blade defined by r/R= 0.24, 0.48, 0.72, and 0.96 using four onboard inertial measurement units. The spanwise flow over the suction surface of the blade was measured using laser Doppler velocimetry (LDV) techniques. The local Reynolds number produced with the test rotor speeds at the measurement locations ranges from 8.31 × 104≤Re∞≤ 9.49 × 105. It was found that rotor aerodynamic efficiency as quantified by the figure of merit is directly linked to blade aspect ratio and the magnitude of spanwise flow over the blade. The rotor with a higher blade aspect ratio produces less overall spanwise flow and is more aerodynamically efficient, however the blade also generates larger mean and fluctuating bending and torsion displacements, which are undesirable for aeroelastic stability. The use of synthetic jets on the blade mitigates the root mean square of the bending and pitch displacements above Ω= 250 RPM and θc= 2°. It was found that at Ω= 1,000 RPM, the blade structures undergo a second mode bending response indicating a condition of structural instability due to higher aerodynamic loading. At this rotor speed, flow control on the outboard of the blade reduces unsteady bending as quantified by arms up to a maximum of 36.5%, and unsteady torsion, θrms up to 22.9% compared to the baseline for the rotor with an aspect ratio of 9.74.

SARS-CoV-2 Spike Protein (RBD) Subunit Adsorption at Abiotic Surfaces and Corona Formation at Polymer Particles.

The adsorption kinetics of the SARS-CoV-2 spike protein subunit with the receptor binding domain at abiotic surfaces was investigated. A combination of sensitive methods was used such as atomic force microscopy yielding a molecular resolution, a quartz microbalance, and optical waveguide lightmode spectroscopy. The two latter methods yielded in situ information about the protein adsorption kinetics under flow conditions. It was established that at pH 3.5–4 the protein adsorbed on mica and silica surfaces in the form of compact quasi-spherical aggregates with an average size of 14 nm. The maximum coverage of the layers was equal to 3 and 1 mg m−2 at pH 4 and 7.4, respectively. The experimental data were successfully interpreted in terms of theoretical results derived from modeling. The experiments performed for flat substrates were complemented by investigations of the protein corona formation at polymer particles carried out using in situ laser Doppler velocimetry technique. In this way, the zeta potential of the protein layers was acquired as a function of the coverage. Applying the electrokinetic model, these primary data were converted to the dependence of the subunit zeta potential on pH. It was shown that a complete acid-base characteristic of the layer can be acquired only using nanomolar quantities of the protein.

Immersed buoyant viscoplastic injections

In this study, the injection of a viscoplastic (yield stress) fluid into a quiescent Newtonian medium is experimentally investigated, using a range of experimental methods, including high-speed camera imaging, laser-induced fluorescence (LIF), and ultrasound Doppler velocimetry (UDV) techniques. The case of our consideration is the continuous downward injection of a Carbopol solution, as a core fluid, through an eccentric inner pipe, placed inside a vertical closed-end pipe filled with a glycerin–water solution. The injected fluid is always heavier than the in-situ fluid and the fluids are miscible. As the injection continues, a filament of the core fluid immersed in the in-situ fluid is formed, for which it has been shown that there exist three distinct flow patterns, namely, the breakup, coiling, and bulging (buckling) regimes. Our focus in this study is to analyse the detailed flow features and sub-regimes at longer times, from an experimental perspective. To generalize our results, they are presented versus the governing dimensionless numbers of the flow, i.e. the buoyancy number, the Bingham number, the viscosity ratio, and the falling height. The breakup regime is analysed in terms of the yielding, necking and pinch-off process, the length of filaments, and their subsequent falling behaviours, the coiling regime in terms of the regular, free and irregular coiling behaviours, and the bulging (buckling) regime in terms of the appearance of a detached falling part and the maximum penetration depth. The results of this work can find applications, in particular, in the plug and abandonment (e.g. cementing processes) of oil and gas wells and 3D printing technologies. • Experimental analysis of immersed buoyant viscoplastic injection in Newtonian fluid. • Observed flow regimes classified into breakup, coiling, and bulging. • Analysis of yielding, necking/pinch-off, and length of filaments for breakup regime. • Coiling subregimes categorized as regular, free, and irregular coiling. • Analysis of maximum penetration depth and subregimes in bulging regime.

METHODS OF ANALYSIS OF T-BURNER EXPERIMENTAL DATA

The measurement of response function for a given solid propellant is mostly done using a T-burner to address the issue of combustion instability in solid rocket motors. Once the experiment has been conducted, it becomes important to carefully analyse and reduce the data to the required response function using the measured pressure. Six different methods of analysing the experimental T-burner data are presented in this paper. An experiment conducted at 1 MPa pressure at 390 Hz frequency is utilized for this purpose. Detailed procedure is given to calculate the growth rate, decay rate and the response function for a self-excited test. These methods include Perry's method, Culick's method and exponential method with different combinations which is reported for the first time. Analyzing with different methods revealed that Culick's method is better and more consistent than the other methods. The response function of the given solid propellant calculated using this method for the self-excited tests of T-burner is in good qualitative agreement with the response measured using Laser Doppler Velocimetry technique.

Aeroelastic response of a propulsive rotor blade with synthetic jets

Understanding the aeroelastic response of a propulsive rotor blade is critical to implementing active flow control techniques to mitigate blade structural vibration. In this experimental study, the coupling between rotor blade aerodynamic loading and first flap mode bending and torsion is explored. The three-bladed rotor is 2.58 m in diameter, and contains a NACA 0012 airfoil with zero pre-built twist. Each blade contains 20 high-performance synthetic jet actuators distributed along the span and are activated with a constant mean jet velocity of 66.3 m/s. The rotor was tested at rotor speeds, Ω of 250, 500, 750, and 1000 revolutions per minute (RPM) and collective blade pitch angles, θc of 2, 5, and 8 degrees. Rotor thrust and torque were measured using a high-capacity load cell, and the flow near the blade tip was measured using laser Doppler velocimetry (LDV) techniques. Blade bending and torsion was measured at three equally spaced radial stations on the blade root, middle, tip regions defined by r/R= 0.32, 0.64, and 0.96 respectively using three onboard electronic accelerometers. Synthetic jets reduce the near-wall streamwise velocity deficit and turbulence intensity in the near wall flow, improving the sectional lift coefficient of the blade and delaying flow separation which results in marginally higher thrust and lower torque loading of up to 7.4% and 4.3 % respectively. At higher rotor speeds of 750 and 1000 RPM, there is a pronounced non-linear increase in bending and torsion along blade span. In the blade tip region, the streamwise flow undergoes a significant decrease in velocity and momentum, which contributes to instabilities in the boundary layer with early-stage unsteady flow separation at θc= 8°. This is correlated to a dramatic rise in the baseline power spectral density (PSD) at the blade’s natural frequency along with an increase in root mean square (rms) of bending acceleration and blade pitch angle, where the maximum values measured are arms= 0.74 g and θrms= 1.45°.

Direct velocity measurements in high-temperature non-ideal vapor flows

Direct velocity measurements in a non-ideal expanding flow of a high temperature organic vapor were performed for the first time using the laser Doppler velocimetry technique. To this purpose, a novel seeding system for insemination of high-temperature vapors was specifically conceived, designed, and implemented. Comparisons with indirectly measured velocity, namely inferred from pressure and temperature measurements, are also provided. Nozzle flows of hexamethyldisiloxane (MM, C_6H_{18}OSi_2) at temperature up to 220,^circ mathrm {C} and pressure up to 10 bar were taken as representative of non-ideal compressible-fluid flows. The relative high temperature, high pressure and the need of avoiding contamination pose strong constraints on the choice of both seeding system design and tracer particle, which is solid. A liquid suspension of tracer particles in hexamethyldisiloxane is injected through an atomizing nozzle in a high-temperature settling chamber ahead of the test section. The spray droplets evaporate, while the particles are entrained in the flow to be traced. Three different test cases are presented: a subsonic compressible nozzle flow with a large uniform region at Mach number 0.7, a high velocity gradient supersonic flow at Mach number 1.4 and a near-zero velocity gradient flow at Mach number 1.7. Temperature, pressure and direct velocity measurements are performed to characterize the flow. Measured velocity is compared with both computational fluid dynamics (CFD) calculations and velocity computed from pressure and temperature measurements. In both cases, the thermodynamic model applied was a state-of-the-art Helmoltz energy equation of state. A maximum velocity deviation of 6.6% was found for both CFD simulations and computed velocity.Graphical abstract

Air swirl effect on spray characteristics and droplet dispersion in a twin-jet crossflow airblast injector

Spray characterization in a novel twin-jet airblast injector is reported in this paper with the focus on the study of the effect of injector air swirl on droplet characteristics and dispersion behavior. The operational principle of the injector is based on achieving atomization of two liquid jets, injected in a radially opposite direction from a central hub by high-speed annular swirling cross-stream flow of air. Liquid jet atomization within model atomizers and the resulting spray study have not gained much attention in spite of its practical importance, for example, in lean premixed prevaporized combustors. In the present work, droplet size and three-component velocity measurements are measured in the above injector using the phase Doppler particle analyzer technique. Air velocity without liquid injection is also obtained using the laser Doppler velocimetry technique. For given inlet air and liquid mass flow rates, experiments are conducted in the absence and presence of annular air swirl corresponding to swirl number, S = 0 and 0.74, respectively. The addition of air swirl is found to dramatically affect the spray topology and also the measured spray characteristics as the droplet size reduces significantly downstream of the injector exit, which is explained. Droplet dispersion is studied by evaluating droplet size velocity correlation and also droplet Stokes number. The results not only provide insight into the physics behind improved atomization due to air swirl, but also demonstrate the ability of the novel injector to achieve atomization quality and high spray dispersion over a wide operating range.

Modulation based ranging for direct displacement measurements of a dynamic surface.

We developed a method for directly measuring displacement of a moving surface for use with dynamic or high explosive driven experiments. The technique, called "Modulation Based Ranging" (MBR), overcomes the errors associated with integrating a velocity history of an object undergoing non-radial flow, while also providing the exact displacement of the object with sub 100 µm resolution. A discussion of sources of phase sensitive errors is presented along with a demonstration of the applied corrections. Excellent agreement between MBR and integrated velocity from the Photonic Doppler Velocimetry (PDV) technique was observed when no non-radial flow was present. We then demonstrated the ability of MBR to accurately measure true displacement of a surface subjected to a strong non-radial component.

Influence of upstream disturbances on performance of an LDV-based cryogenic flow meter standard – CFD modelling and preliminary measurements with air

Increasing trade of liquefied natural gas (LNG) imposes stringent requirements for accurate flow rate measurement of this high energy content fluid. To satisfy this demand, a flow meter has been developed by CEASAME Exadebit which is based on velocity measurement behind a contraction nozzle using Laser Doppler Velocimetry technique (LDV). For this instrument, a calibration factor is defined relating the measured velocity to the flow rate. This calibration factor depends on the Reynolds number and it can be sensitive to the velocity profile behind the nozzle outlet and to presence of upstream flow disturbances such as bends, valves, etc. when the meter is installed on-site. In this paper, CFD modelling, using OpenFoam software, was employed to analyse the sensitivity of the calibration factor to flow disturbances for two types of disturbing elements; a U-bend and half-plate orifice. The CFD model was validated by comparison with experimental data for the calibration factor and velocity profiles obtained from preliminary LDV measurements with air. Two measurement setups were considered where the velocity is measured either in one point at the nozzle axis or integrated along a line across the nozzle diameter. The results show that the considered disturbing elements cause deviations in the calibration factor in the order of tenths of percent and that the maximal sensitivity of the line-setup to these disturbances is approximately half of the maximal sensitivity of the point-setup. On the other hand, it was shown that the line-setup is more sensitive to the LDV positioning than the point-setup.

On the figure of merit and streamwise flow of a propulsive rotor with synthetic jets

Increasing the figure of merit of propulsive rotors for vertical takeoff and landing (VTOL) vehicles is critical to improving the hover efficiency and flight endurance of rotorcraft. In this paper, a new flow control scheme is proposed where 60 synthetic jet actuators are utilized on a large-scale propulsive rotor and the jets' velocity is increased from the blade root to the blade tip in order maintain constant levels of momentum coefficient per blade module. The three-bladed rotor measures 2.58 m in diameter and contains a NACA 0012 airfoil with zero blade twist distribution. The rotor was tested at speeds of 250, 500, 750 and 1,000 revolutions per minute (RPM) and blade pitch angles of 2, 5, and 8 degrees. Rotor thrust and power were measured using a high-capacity load cell and current sensor, and the streamwise flow was measured using phased-locked laser Doppler velocimetry (LDV) techniques at two measurement planes near the blade root and near the blade tip along the suction surface of the airfoil. Two flow control schemes were tested and compared; the new constant momentum coefficient (constant Cμ) and non-constant Cμ where the synthetic jet velocity is held constant throughout the rotor blade. When all 20 synthetic jets per blade are activated, it was found that constant Cμ improves low-speed rotor performance in terms of figure of merit, FM and thrust coefficient, CT at 250 RPM, while non-constant Cμ is marginally superior at higher rotor speeds. When both flow control schemes are applied for just the blade root module, an increase in performance compared to the baseline is observed at rotor speeds of 750 and 1000 RPM, however different values of FM and CT are achieved for each scheme. Near the blade tip the boundary layers undergo transition to turbulent flow combined with an increasing degree of adverse pressure gradient with rotor speed and blade pitch angle. Under these conditions where the normalized streamwise velocity profiles show significant velocity deficit in the near-wall flow, synthetic jets provide some momentum to delay separation as quantified by the boundary layer shape factor.

Accuracy of the interferometric method for Leeb hardness testers calibration.

In this article, we propose a method for improving accuracy in calibrating Leeb hardness testers using fiber interferometric systems. The calibration system is implemented using the photonic Doppler velocimetry technique. This paper provides estimates of the measurement uncertainty arising in the calibration system and describes a method for improving accuracy, which takes into account the signal-to-noise ratio, sampling rate, and processing parameters.

Application of the Photon Doppler Velocimetry (PDV) technique in tension-torsion Hopkinson bar experiments

The Photon Doppler Velocimetry (PDV) technique is used to capture simultaneously propagating elastic waves of longitudinal and shear nature in a Tension-Torsion Hopkinson Bar (TTHB) apparatus. The system uses a pair of probes per velocity measurement, which were taken on the opposite sides of the TTHB bar with a laser irradiated spot size of ~35 µm. The collected data were compared to the measurements obtained from the conventional strain gauge technique, and were in good agreement. The PDV method was effective in separating longitudinal and rotation signals even when they were superimposed on each other at the gauge location. This approach is also shown to be effective in detecting and accounting for the presence of bending waves in the TTHB bars.

Effect of electromagnetically driven liquid metal flows on the electric potential difference in a cuboid vessel

In this work, we study the effect on the electric potential difference (EPD) of a liquid metal (LM) flow confined in a cuboid vessel. The interaction between a magnetic field (MF) and an electric current density (j0) along the ascending axial direction generates a Lorentz force that stirs the LM producing an MHD flow. The MF is produced by either a single or a pair of NdFeB dipolar permanent magnets. j0 is in the range of 384 to 1153 A m-2. Experimental characterization is done by measuring velocity components using the ultrasound Doppler velocimetry (UDV) technique and measurements of the EPD in terminals of the vessel. Additionally, an MHD model is solved using the COMSOL Multiphysics software. A good agreement between measurements and simulations for the magnetic and velocity fields is obtained. Furthermore, an order of magnitude analysis for the characteristic velocity of the flow and EPD is presented. Comparing with a configuration without magnets, the EPD when one magnet is used reaches 16.8% higher values. In contrast, for a pair of magnets values are 22.9% smaller. This increasing/decreasing behavior for the EPD with the flow patterns could be of interest to applications such as liquid metal batteries.

Measurement of admittance and acoustic augmentation of burning rate of composite solid propellants using Laser Doppler Velocimetry

The present work involves the use of Laser Doppler Velocimetry (LDV) technique to measure the acoustic admittance of aluminized composite solid propellant (AP/HTPB/Al) by experimentally measuring the instantaneous velocities of the particles of solid propellant during burning while the acoustic pressure oscillations are being imposed. Both velocity fluctuations and pressure fluctuations are measured synchronously. The probe volume of the laser is maintained at a constant distance from the burning surface by using a linear actuator. Tests were conducted for two aluminized composite solid propellants at low frequency ranges (130-312 Hz) of the longitudinal acoustic modes and mean chamber pressures ranging from 1 to 4 MPa. A rotary valve is designed to acoustically excite the chamber to the required resonant frequency. It was found that admittance rises with frequency and peaks around 260 Hz and then falls. The use of linear actuator mechanism significantly improves the velocity data rate (number of data points). Maintaining the probe volume at 800 to 900 µm above the propellant surface is very crucial to determine the admittance accurately. Test results revealed that a good agreement between the steady state mean burning rates with the window bomb experiments is achieved. The measured mean burn rates under imposed acoustic pressure oscillations shows the augmentation up to 55%. The admittance measured for the metallized composite propellant using this technique and the comparison with T-burner shows good agreement. The comparison of responses with LDV and T-burner and the augmentation factor due to acoustic oscillations using LDV are reported for the first time.

Liquid Metal Flow Under Traveling Magnetic Field—Solidification Simulation and Pulsating Flow Analysis

Non steady applied magnetic field impact on a liquid metal has good prospects for industry. For a better understanding of heat and mass transfer processes under these circumstances, numerical simulations are needed. A combination of finite elements and volumes methods was used to calculate the flow and solidification of liquid metal under electromagnetic influence. Validation of numerical results was carried out by means of measuring with ultrasound Doppler velocimetry technique, as well as with neutron radiography snapshots of the position and shape of the solid/liquid interface. As a result of the first part of the work, a numerical model of electromagnetic stirring and solidification was developed and validated. This model could be an effective tool for analyzing the electromagnetic stirring during the solidification process. In the second part, the dependences of the velocity pulsation amplitude and the melt velocity maximum value on the magnetic field pulsation frequency are obtained. The ability of the pulsating force to develop higher values of the liquid metal velocity at a frequency close to the MHD resonance was found numerically. The obtained characteristics give a more detailed description of the electrically conductive liquid behaviour under action of pulsating traveling magnetic field.

Characteristics and analysis of a turbulent offset jet including the effect of density and offset height

This paper presents the results of measurements and numerical predictions of 3D turbulent offset jet flows. Mean velocity and turbulence characteristics of a rectangular offset jet with different offset heights and within variable densities are experimentally and numerically investigated in detail. Four jet gas exit densities, ρj = 1.2, 1.25, 1.3 and 1.4 Kg/m3, and four offset ratios, h/w = 8, 16, 25 and 33, are studied. The considered variation of the jet density is revealed at different Reynolds numbers and the velocity measurements are carried out using a Laser Doppler Velocimetry (LDV) technique. The handled configuration is numerically simulated by solving the Navier-Stokes equations with the finite volume method having a non-uniform grid system. Two different closure models are tested: the standard k–ε model and the Reynolds Stress Model (RSM). Results clearly revealed significant effects of the jet density and the offset height on the flow development in the early region. It is noted that the centerline velocity decay increases as the jet density and the offset height increase. It is also observed that the reattachment length of the jet decreases with the increase of the jet density. However, the reattachment length is found to increase with the increase of the offset height.