Tangential Velocity Components Research Articles

NETWORK NUMERICAL ANALYSIS OF OPTICALLY THICK HYDROMAGNETIC SLIP FLOW FROM A POROUS SPINNING DISK WITH RADIATION FLUX, VARIABLE THERMOPHYSICAL PROPERTIES, AND SURFACE INJECTION EFFECTS

The steady, incompressible, laminar Newtonian magnetohydrodynamic slip flow with heat transfer from an impulsively started, spinning porous disk is investigated when strong injection (blowing) and significant thermal radiation heat transfer are present. The properties of the fluid, i.e., density, viscosity, and thermal conductivity, are assumed to vary with temperature. Using appropriate transformations, the axisymmetric flow conservation equations for mass, momentum, and energy in a cylindrical polar coordinate system (r, ϕ, z) are normalized to yield a series of highly nonlinear, coupled ordinary differential equations that are solved under appropriate boundary conditions with the network simulation method (NSM). Comparisons are made with an earlier study for the case of Prandtl number = 0.64 with suction present and found to be in excellent agreement. The effects of the radiation-conduction parameter (Nr), hydromagnetic parameter (Nm), slip factor (γ, which is related to Knudsen number), uniform injection parameter (W > 0), and temperature difference parameter (ϵ) on the axial, radial, and tangential velocity components, Nusselt number, and temperature function are investigated in detail. Applications of the study include turbine blade systems, magnetic field control of chemical engineering processes, and electronic computer disk drive cooling.

Numerical simulation and control of horseshoe vortex around an appendage–body junction

The horseshoe vortex generated around the appendage–body junction of submarines strongly influences the non-uniformity of submarine wakes at the propeller discs. The flow characteristics around the appended submarine body are numerically simulated and analyzed, and a new method on the vortex control baffle is presented. Then, the influence of the vortex control baffle on the horseshoe vortex generated at the sail–body junction is numerically studied, and the flow phenomena caused by the vortex control baffle with different transverse positions is investigated further. Results show that the vortex control baffle can induce a kind of attached vortex in a rotational direction opposite to the horseshoe vortex; these two kinds of vortices undermine each other. Furthermore, when the transverse position of the vortex control baffle is close to the horseshoe vortex, the state of the horseshoe vortex is directly affected, and the flow structure becomes even more complex. We adapt the vortex control baffle for the horseshoe vortex generated at the stern foil–body junction. Results from the numerical simulation of the flow around the fully appended submarine model indicate that the effect of the vortex control baffle greatly improves the performance of the submarine wake. The circumferential non-uniformity of the axial, tangential, and radial velocity components are decreased markedly. The engineering applicability of the vortex control baffle has been well presented.

Experimental investigation of tornado-like vortex dynamics with swirl ratio: The mean and turbulent flow fields

An experimental simulation of tornado-like vortices is conducted in a small tornado vortex simulator in order to study the effect of swirl ratio on flow characteristics. Particle Image Velocimetry (PIV) method is employed to quantitatively determine the tornado-vortex velocity field for swirl ratios ranging from 0.08 to 1. The radial and tangential components of velocity as well as the core radius of the tornado increase with increase in swirl ratio. The location of the maximum radial and tangential velocities is adjacent to the ground where the tornado vortex interacts with the surface. The values of normal and shear turbulent stresses indicate the existence of a laminar core for small swirl. As expected the shear stresses increase with swirl ratio as the vortex becomes turbulent. The highest turbulent production corresponds to the critical case of vortex touchdown.

Simulating turbulent swirling flow in a gas cyclone: A comparison of various modeling approaches

The single phase flow field of a gas cyclone has been simulated with a finite volume RANS model and two LES approaches — one with finite volume and one with lattice-Boltzmann discretization. In order to evaluate their quality, the modeling results have been compared with LDA velocity measurements taken from the literature. Since the steady-state RANS simulation did not result in a converged solution, an unsteady RANS simulation was performed and used for further evaluations. The peak-levels of the time-averaged tangential velocity are well predicted by the two LES approaches whereas the RANS-based simulation under-predicts them. For the mean axial velocity, all models perform equally well. Velocity fluctuation levels (in terms of the root-mean-square values of the tangential and axial velocity components) are much better predicted by the large eddy simulations as compared to the RANS simulation. This relates to vortex core precession, the frequency of which was analysed for the two LES approaches. It agreed within 10% with experimentally obtained data. In conclusion, unsteady RANS-based simulations on a relatively coarse grid can provide reasonable and industrially relevant results with limited computational effort, whereas simulations that accurately capture the flow physics require a large eddy approach on fine grids.

Overspray and Interstage Fog Cooling in Gas Turbine Compressor Using Stage-Stacking Scheme—Part II: Case Study

A stage-by-stage wet compression theory and algorithm have been developed for overspray and interstage fogging in the compressor. These theory and algorithm are used to calculate the performance of an eight-stage compressor under both dry and wet compressions. A 2D compressor airfoil geometry and stage setting at the mean radius are employed. Six different cases with and without overspray are investigated and compared. The stage pressure ratio enhances during all fogging cases as does the overall pressure ratio, with saturated fogging (no overspray) achieving the highest pressure ratio. Saturated fogging reduces specific compressor work, but increases the total compressor power due to increased mass flow rate. The results of overspray and interstage spray unexpectedly show that both the specific and overall compressor power do not reduce but actually increase. Analysis shows that this increased power is contributed by the increased pressure ratio and, for interstage overspray, “recompression” contributes to more power consumption. Also it is unexpected to see that air density actually decreases, instead of increases, inside the compressor with overspray. Analysis shows that overspray induces an excessive reduction in temperature that leads to an appreciable reduction in pressure, so the increment of density due to reduced temperature is less than the decrement of air density affected by reduced pressure as air follows the polytropic relationship. In contrast, saturated fogging results in increased density as expected. After the interstage spray, the local blade loading immediately showed a significant increase. Fogging increases axial velocity, flow coefficient, blade inlet velocity, incidence angle, and tangential component of velocity. The analysis also assesses the use of an average shape factor in the generalized compressor stage performance curve when the compressor stage information and performance map are not available. The result indicates that using a constant shape factor might not be adequate because the compressor performance map may have changed with wet compression. The results of nonstage-stacking simulation are shown to underpredict the compressor power by about 6% and the net gas turbine output by about 2% in the studied cases.

Experimental validation of alternate integral-formulation method for predicting acoustic radiation based on particle velocity measurements

This paper presents experimental validation of an alternate integral-formulation method (AIM) for predicting acoustic radiation from an arbitrary structure based on the particle velocities specified on a hypothetical surface enclosing the target source. Both the normal and tangential components of the particle velocity on this hypothetical surface are measured and taken as the input to AIM codes to predict the acoustic pressures in both exterior and interior regions. The results obtained are compared with the benchmark values measured by microphones at the same locations. To gain some insight into practical applications of AIM, laser Doppler anemometer (LDA) and double hotwire sensor (DHS) are used as measurement devices to collect the particle velocities in the air. Measurement limitations of using LDA and DHS are discussed.

Observations of the initial 3D flow from a ship's propeller

The present paper was aimed at presenting the time-averaged velocity and turbulence intensity at the initial plane from a ship's propeller. The flow characteristics of a ship's propeller jet are of particular interest for the researchers investigating the jet induced seabed damage as documented in the previous studies. Laser Doppler Anemometry (LDA) measurements show that the axial component of velocity is the main contributor to the velocity magnitude at the initial plane of a ship's propeller jet. The tangential component contributes to the rotation while the radial component which contributes to the diffusion, are the second and third largest contributors to the velocity magnitude. The maximum tangential and radial velocity components at the initial plane are approximately 82% and 14% of the maximum axial velocity component, respectively. The axial velocity distribution at the initial plane shows two peaked ridges with a low velocity core at the rotation axis. The turbulence intensity distribution shows a three-peaked profile at the initial plane.

Quasi-specular reflection of cold neutrons from nano-dispersed media at above-critical angles

We have predicted and observed for the first time a new phenomenon of quasi-specular reflection of cold neutrons at small incidence angles from nano-dispersed media. this is due to multiple small-angle scattering of neutrons from nano-sized inhomogeneities in the scattering potential. The reflection angle as well as the half-width of angular distribution of diffusively reflected neutrons is approximately equal to the incidence angle. For the powder of diamond nanoparticles used, the reflection probability was equal to ∼30% within the detector angular size, which corresponds to 40–50% of total probability (albedo) of quasi-specular reflection. The tangential velocity component of incident neutrons was up to an order of magnitude larger than the critical velocity for pure diamond. We provide an example of potential application of the discovered phenomenon for increasing cold neutron fluxes available for experiments.

Axial Flow Fan Tip Leakage Flow Control Using Tip Platform Extensions

Performance of an axial flow fan unit is closely related to its tip leakage mass flow rate and level of tip/casing interactions. The present experimental study uses a stereoscopic particle image velocimeter to quantify the three dimensional mean flow observed near the blade tip, just downstream of a ducted fan unit. After a comprehensive description of the exit flow from the baseline fan, a number of novel tip treatments based on custom designed pressure side extensions are introduced. Various tip leakage mitigation schemes are introduced by varying the chordwise location and the width of the extension in the circumferential direction. The current study shows a proper selection of the pressure side bump location and width are the two critical parameters influencing the success of each tip leakage mitigation approach. Significant gains in the axial mean velocity component are observed when a proper pressure side tip extension is used. It is also observed that a proper tip leakage mitigation scheme significantly reduces the tangential velocity component near the tip of the axial fan blade. Reduced tip clearance related flow interactions are essential in improving the energy efficiency of ducted fan systems. A reduction or elimination of the momentum deficit in tip vortices is also essential to reduce the adverse performance effects originating from the unsteady and highly turbulent tip leakage flows rotating against a stationary casing.

Behavior of a small single bubble rising in rotating flow field

A small single bubble was generated with a single-hole nozzle facing upward in a water bath contained in a rotating cylindrical vessel. The bubble size falls in the surface tension force dominant regime. The vertical, radial, and tangential migration velocities of the bubble were measured with two CCD cameras and a high-speed video camera. The tangential velocity component of water flow was measured with particle image velocimetry. A helical motion of the bubble was observed under every experimental condition. The direction of the helical motion was the same as that of the tangential velocity component. This helical motion is associated with the large initial shape deformation of the bubble near the nozzle exit and the subsequent regular shedding of vortices behind it. The period and amplitude of the helical motion were obtained by analyzing the trajectory of the bubble. These quantities were non-dimensionalized by the volume equivalent bubble diameter and the terminal bubble velocity in the vertical direction and correlated as functions of the Eotvos number. Empirical equations were proposed for the period and amplitude.

Polarization of X-ray lines from galaxy clusters and elliptical galaxies - a way to measure the tangential component of gas velocity

We study the impact of gas motions on the polarization of bright X-ray emission lines from the hot intercluster medium (ICM). The polarization naturally arises from resonant scattering of emission lines owing to a quadrupole component in the radiation field produced by a centrally peaked gas density distribution. If differential gas motions are present then a photon emitted in one region of the cluster will be scattered in another region only if their relative velocities are small enough and the Doppler shift of the photon energy does not exceed the line width. This affects both the degree and the direction of polarization. The changes in the polarization signal are in particular sensitive to the gas motions perpendicular to the line of sight. We calculate the expected degree of polarization for several patterns of gas motions, including a slow inflow expected in a simple cooling flow model and a fast outflow in an expanding spherical shock wave. In both cases, the effect of non-zero gas velocities is found to be minor. We also calculate the polarization signal for a set of clusters, taken from large-scale structure simulations and evaluate the impact of the gas bulk motions on the polarization signal. We argue that the expected degree of polarization is within reach of the next generation of space X-ray polarimeters.

Numerical investigations of the effect of oblique impact on particle deformation in cold spraying by the SPH method

In this study, a systematic examination of the oblique impacting of copper particles in cold spraying was conducted by using the smoothed particle hydrodynamics (SPH) method compared to the Lagrangian method. 3D models were employed owing to the asymmetric characteristic of the oblique impacting. It is found that in the oblique impact, the additional tangential component of particle velocity along the substrate surface could create a tensile force and decrease the total contact area and bonding strength between the particle and the substrate. The simulation results compare fairly well to the experiment results. Meanwhile, the asymmetric deformation can result in the focus of the shear friction on a small contact zone at one side, which may rise the interfacial temperature and thus facilitate the occurrence of the possible shear instability. Therefore, there probably exists an angle range, where the deposition efficiency may be promoted rather than the normal angle. Moreover, the particle deformation behavior simulated by the SPH method is well comparable to that simulated by the Lagrangian method and the experimental results, which indicates the applicability of the SPH method for simulating the impact process in cold spraying besides the previously used Arbitrary Lagrangian Eulerian (ALE) method.

A Controllable Twin- Fluid Internally Mixed Swirl Atomizer

The atomizer serves as an energy conversion mechanism to convert a volume of the liquid into a multiplicity of small droplets and then ejects these droplets so as to produce a high ratio of surface to mass in the liquid phase and thereby achieve high rates of mixing and evaporation. For the current needs, a compact configuration arrangement is needed to meet the design requirements of small volume and high maintenance availability. As compared with the traditional design, the new atomizer designs should possess better energy conversion efficiency (from pressure to kinetic energy). The technique of combining two or more principles has well served in the field of atomization in the past. The drawbacks of one type of atomizer can be overcome by combining it with other types of atomizer, in what is generally referred to as a hybrid atomizer. The atomizer discussed in this paper combines the principles of twin-fluid internally mixed atomizers and conventional pressure swirl atomizers to produce a spray the characteristics of which can be controlled over a wide range of operating conditions. Atomization of liquids is widely used in several applications, e.g. spray combustion, spray-painting, spray drying, crop spraying and many other applications. In some atomizer applications the control of droplet and/or particle size is very critical. In some applications, extremely small droplets are preferred (less than a micron), while in others, droplet diameters on the scale of several hundred microns are required. Spray combustion is used in domestic heating burners, industrial heating furnaces, gas turbines, diesel engines and rockets. For the different applications, a wide range of spray devices have been developed and they are generally designated as atomizers and nozzles (1-3). Spray may be produced in various ways. The process of atomization is a process where a liquid jet or sheet is broken up by the kinetic energy of the liquid itself or by exposure to high- velocity air or gas. Some atomizers accomplish this by discharging liquid at high velocity into a relatively slow-moving stream of air or gas. Examples of this type of atomizers include various forms of pressure atomizers and also rotary atomizers that eject the liquid at high velocity from the periphery of rotating disc. An alternative approach is to expose a relatively slow-moving liquid to a high- velocity air stream. This method is generally known as twin- fluid, air-assist or air-blast atomization. In the context of the present invention, it is worthwhile to mention about the conventional swirl atomizer and an internally mixed atomizer reported in the prior art. In swirl atomizer liquid is made to flow through a swirler before it exits from the atomizer, providing a tangential motion to the liquid. This swirling liquid forms a hollow cone outside the atomizer and this cone breaks up into droplets once the kinetic energy of the molecules of the cone overcomes the surface energy of the liquid. In an internally mixed atomizer, a small amount of gas is introduced into the liquid inside the injector forming a two-phase mixture of liquid and gas. This two-phase mixture produces liquid droplets owing to two-phase flow dynamics. However, due to the absence of any tangential velocity component in the flow (because it is a one dimensional flow), this atomizer always forms a solid cone spray.

Remote gas sampling with a swirl air stream

One of the promising techniques of remote gas sampling from the surface or from the inside of an object involves the use of a swirl air stream. The case in which a swirl sampling stream produces a vortex core of a composite swirl is of most interest. But a practical implementation of a vortex sampling faces major problems due to the fact that the majority of the available gas analyzers feature a low analytical flow. This offers limitations on sampling distance and reduced pressure created at the object surface. This paper deals with the problem of adjusting vortex and sampling flows for a mass-spectrometer with atmospheric pressure ionization used for remote sampling of diethylanyline vapors. It is shown experimentally that additional sampling flow (Q(add)) that coaxially envelops an analytical channel allows one to achieve conditions required for the formation of a vortex core, which is characterized by an increased tangential component of the flow velocity at its boundary and abnormally low pressure on the core axis. A satisfactory agreement between the calculations by the composite vortex model and the experiment is obtained. The studies performed have shown that the optimal relationship between vortex (Q(vortex)) and additional flows is Q(vortex)/Q(add)=1.3 and is symbate in terms of both gas dynamic parameters (minimal diameter of a backflow core) and sampling efficiency. It is shown that both the sampling distance and sampling area depend mainly on geometric sampler parameters. The experiments performed have revealed the unique ability of a vortex sampling flow in the form of a composite vortex to focus the sample inside the vortex core, thus preventing its dilution over the backflow.

Evolution of Tip Vortices Generated by Two Bladed Rotor in Hover at Early Wake Ages

In order to investigate change of vortex structures and its evolving processes, two dimensional LDV system was used for measurement of velocity vectors of tip vortex, and PIV system was also used for visualizations of tip vortex array for two bladed rotor, respectively. Experiments provided vortex locations, tangential and axial velocity components of tip vortex at six wake ages of 9.5, 10.5, 60.5, 99.5, 129.5, 169.5 and corresponded six wake ages shifted with 180 degrees per each. It was resulted that tip vortices generated by the first blade satisfy Landgrebe’s model for their vortex locations even after they were accelerated by the second blade in downstream. Tangential velocity components of tip vortices follow Vatistas’ n=2 model on both inside and outside regions of rotor slipstream without loss of vortex circulation. Axial velocity profiles revealed that there were small but significant perturbations just outside the primary vortex core which implies the second blade affects the wake substantially. It was also found that tip paths of each blade were not willing to be coincided intrinsically.

Condensation-induced kinematics and dynamics of cyclones, hurricanes and tornadoes

A universal equation is obtained for air pressure and wind velocity in cyclones, hurricanes and tornadoes as dependent on the distance from the center of the considered wind pattern driven by water vapor condensation. The obtained theoretical estimates of the horizontal profiles of air pressure and wind velocity, eye and wind wall radius in hurricanes and tornadoes and maximum values of the radial, tangential and vertical velocity components are in good agreement with empirical evidence.

Processes and equipment for chemical and oil-gas production

Results are presented for investigations and analyses of straight-through centrifugal separation elements simultaneously fulfilling the function of the coalescence (enlargement) of drops, which makes it possible to improve the effectiveness of the centrifugal-separation process, and the function of drop separation from a gaseous flow. A mathematical model is presented for determination of drop diameter as a function of radius of the stationary installed ejector (deflector) along the axis of a straight-through centrifugal element, the difference between the densities of the liquid and gas, the surface tension of the liquid, and the tangential velocity component of the flow. Coalescence of liquid drops is confirmed not only by computational relationships, but also by photographs obtained during experiments.

A Study on the Flow Characteristics of the Spiral Flow Nozzle with the Width Change of Annular Slit

In comparison with previous researches fur swirling flow, the spiral flow self-generated in the spiral flow nozzle has some different characteristics. It is not needed a compulsive tangential momentum to get its velocity component and has long potential core, relatively low swirl ratio, and high focusing ability. In this study, the self-generated mechanism of the spiral flow was clarified and the effect on the width of annular slit on spiral flow characteristics was investigated experimentally and numerically. As a result, the existence of tangential velocity component regardless of a compulsive angular momentum is clarified and the results obtained by experiment have a satisfactory agreement with those by numerical method, quantitatively and qualitatively.

Investigation of spiral blood flow in a model of arterial stenosis

The spiral component of blood flow has both beneficial and detrimental effects in human circulatory system [Stonebridge PA, Brophy CM. Spiral laminar flow in arteries? Lancet 1991; 338: 1360–1]. We investigate the effects of the spiral blood flow in a model of three-dimensional arterial stenosis with a 75% cross-sectional area reduction at the centre by means of computational fluid dynamics (CFD) techniques. The standard k– ω model is employed for simulation of the blood flow for the Reynolds number of 500 and 1000. We find that for Re = 500 the spiral component of the blood flow increases both the total pressure and velocity of the blood, and some significant differences are found between the wall shear stresses of the spiral and non-spiral induced flow downstream of the stenosis. The turbulent kinetic energy is reduced by the spiral flow as it induces the rotational stabilities in the forward flow. For Re = 1000 the tangential component of the blood velocity is most influenced by the spiral speed, but the effect of the spiral flow on the centreline turbulent kinetic energy and shear stress is mild. The results of the effects of the spiral flow are discussed in the paper along with the relevant pathological issues.

Is the Milky Way ringing? The hunt for high-velocity streams

Abstract We perform numerical simulations of a stellar galactic disc with initial conditions chosen to represent an unrelaxed population which might have been left following a merger. Stars are unevenly distributed in radial action angle, though the disc is axisymmetric. The velocity distribution in the simulated solar neighbourhood exhibits waves travelling in the direction of positive v, where u, v are the radial and tangential velocity components. As the system relaxes and structure wraps in phase space, the features seen in the u–v plane move closer together. We show that these results can be obtained also by a semi-analytical method. We propose that this model could provide an explanation for the high-velocity streams seen in the solar neighbourhood at approximate v in kms−1, of −60 (HR1614), −80, −100 (Arcturus) and −160. In addition, we predict four new features at v≈−140, −120, 40 and 60kms−1. By matching the number and positions of the observed streams, we estimate that the Milky Way disc was strongly perturbed ∼1.9Gyr ago. This event could have been associated with Galactic bar formation.