Swirl Velocity Distribution Research Articles

Influence of PST and PHF heating conditions on the swirl flow of Al+Mg+TiO2 ternary hybrid water-ethylene glycol based nanofluid with a rotating cone

Swirl flow heat exchangers are commonly used in industrial processes such as power generation, chemical processing, and refrigeration. They can be used for both heating and cooling applications and can be designed to handle a wide range of fluid flow rates and temperatures. This study investigated the influence of PST (prescribed surface temperature) and PHF (prescribed heat flux) heating conditions on the swirl flow of Al+Mg+TiO2 ternary hybrid water-ethylene glycol (50/50) based nanofluid with a heated rotating cone. The governing ordinary differential equations were derived from the partial differential equations using the proper similarity transformations. The problem was solved using the Shifted Legendre Collocation Method (SLCM), which is a powerful numerical method. The results showed that the PST heating conditions had a significant impact on the flow and heat transfer characteristics of the ternary hybrid nanofluid. Under PHF heating conditions, the swirl velocity distribution was leading to a noteworthy influence. The use of the Al+Mg+TiO2 ternary hybrid water-ethylene glycol based nanofluid resulted in a significant enhancement in the convective heat transfer coefficient. The SLCM method provided accurate and efficient numerical solutions for the problem, demonstrating its suitability for simulating complex fluid flow and heat transfer problems.

Inlet swirl decay and mixing in a laminar micro-pipe flow with wall slip

In this work, the decaying laminar inlet swirl flow in a straight circular micro-pipe with wall slip is solved analytically and the solution is verified numerically. Based on a fully developed parabolic axial velocity profile, the swirl velocity equation is solved by the separation of variables technique. The solution is expressed as a function of the flow Reynolds number, the axial distance within the circular micro-pipe from the inlet, the wall slip, and the inlet swirl velocity profile. The effects of the parameters on the swirl velocity distribution and the swirl decay are analyzed along the flow. The addition of swirling velocity to the flow of a fluid in a pipe is of great importance in the enhancement of transport characteristics. The current results offer analytical equations to estimate the swirl velocity distribution with slip at the walls for the design of swirl flow devices. Furthermore, to quantify mixing, the change in the average distance traveled by fluid particles from the inlet in a swirl flow is compared with the average distance traveled by the fluid particles in the case of no swirl. A clear enhancement of the average distance traveled is obtained for flows with the interaction of both swirl and slip effects. In our opinion, the present work is useful to researchers looking for the enhancement of transport characteristics in circular micro-pipes.

Actuator line simulations of a Joukowsky and Tjæreborg rotor using spectral element and finite volume methods

The wake structure behind a wind turbine, generated by the spectral element code Nek5000, is compared with that from the finite volume code EllipSys3D. The wind turbine blades are modeled using the actuator line method. We conduct the comparison on two different setups. One is based on an idealized rotor approximation with constant circulation imposed along the blades corresponding to Glauert's optimal operating condition, and the other is the Tjffireborg wind turbine. The focus lies on analyzing the differences in the wake structures entailed by the different codes and corresponding setups. The comparisons show good agreement for the defining parameters of the wake such as the wake expansion, helix pitch and circulation of the helical vortices. Differences can be related to the lower numerical dissipation in Nek5000 and to the domain differences at the rotor center. At comparable resolution Nek5000 yields more accurate results. It is observed that in the spectral element method the helical vortices, both at the tip and root of the actuator lines, retain their initial swirl velocity distribution for a longer distance in the near wake. This results in a lower vortex core growth and larger maximum vorticity along the wake. Additionally, it is observed that the break down process of the spiral tip vortices is significantly different between the two methods, with vortex merging occurring immediately after the onset of instability in the finite volume code, while Nek5000 simulations exhibit a 2-3 radii period of vortex pairing before merging.

Forward sweep to improve the efficiency of rotor-only tube-axial fans with controlled vortex design blades

Common blade design techniques are based on the assumption of the airflow laying on cylindrical surfaces. This behaviour is proper only for free-vortex flow, whereas radial fluid migration along the span is always present in case of controlled vortex design blades. The paper presents a design procedure to increase aeraulic efficiency of fan rotors originally designed using a controlled vortex criterion, based on the assumption that a blade section positioning taking into account the actual airflow direction could be beneficial for rotor aeraulic performance. The proposed procedure employs a three-dimensional aerofoil positioning and blade forward sweep. The procedure is applied to a rotor-only tube-axial fan featuring a 0.44 hub-to-tip ratio, an almost constant swirl velocity distribution at the rotor outlet and a quite low blade Reynolds number. Rotor prototypes deriving from step-by-step blade modifications are experimentally tested on an ISO 5801 standard test rig. Results show the importance of considering radial fluid migration for highly loaded rotors.

Investigation of wind turbine flow and wake

This paper is dedicated to the investigation and analysis of wind turbine wake. An experimental work is undertaken in wind tunnel on a horizontal axis wind turbine model. The velocity field in the wake is measured using PIV with phase synchronization in order to relate velocity and vortices to the rotating blades. The tip vortices are investigated in successive azimuthal positions of the rotor. A specially developed algorithm based on the circulation maximum detects the positions of the vortex cores and permits to use conditional averaging technique. The analysis of obtained velocity fields enables to determine the vortex core diameter, the swirl velocity distribution and the vortex diffusion as functions of the vortex age. The quality of obtained results permits to use them as reference for the validation of numerical computations.

Analytical solutions of laminar swirl decay in a straight pipe

In this work, the laminar swirl flow in a straight pipe is revisited and solved analytically by using prescribed axial flow velocity profiles. Based on two axial velocity profiles, namely a slug flow and a developed parabolic velocity profiles, the swirl velocity equation is solved by the separation of variable technique for a rather general inlet swirl velocity distribution, which includes a forced vortex in the core and a free vortex near the wall. The solutions are expressed by the Bessel function for the slug flow and by the generalized Laguerre function for the developed parabolic velocity. Numerical examples are calculated and plotted for different combinations of influential parameters. The effects of the Reynolds number, the pipe axial distance, and the inlet swirl profiles on the swirl velocity distribution and the swirl decay are analyzed. The current results offer analytical equations to estimate the decay rate and the outlet swirl intensity and velocity distribution for the design of swirl flow devices.

A constant shear stress core flow model of the bidirectional vortex

In this paper, we discuss the merits of two models for the swirl velocity in the core of a confined bidirectional vortex. The first is piecewise, Rankine-like, based on a combined-vortex representation. It stems from the notion that a uniform shear stress distribution may be assumed in the inner vortex region of a cyclone, especially at high Reynolds numbers. Thereafter, direct integration of the shear stress enables us to retrieve an expression for the swirl velocity that overcomes the inviscid singularity at the centreline. The second model consists of a modified asymptotic solution to the problem obtained directly from the Navier–Stokes equations. Both solutions we present transition smoothly to the outer, free-vortex approximation at some intermediate position in the chamber. This position is deduced from available experimental data to the extent of providing an accurate swirl velocity distribution throughout the chamber. By scaling the constant shear radius to the core layer thickness, the constant of proportionality is readily calculated using the method of least squares. Interestingly, the constant of proportionality is found to be invariant at several vortex Reynolds numbers, thus helping to achieve closure. The combined-vortex representation is validated against a large body of experimental measurements and through comparisons to a laminar core model that is enhanced through the use of an eddy viscosity. Other heuristic schemes are discussed and the two most suitable models to capture realistic flow behaviour at high vortex Reynolds numbers are identified. Our two models are first derived analytically and then anchored on the available experimental measurements.

회전 유도탄의 추진 제트에 의한 롤 댐핑 해석

롤 회전하는 유도탄에서 축소-확대 노즐을 지나는 추진 제트와 유도탄과의 각운동량 교환을 통하여 유도탄의 각운동량이 증가하게 되고 이러한 현상을 제트 롤 댐핑이라 한다. 본 연구에서는 제트 롤 댐핑을 각운동량 보존 방정식으로부터 유도하고 근사적인 계산을 통하여 신궁 유도탄의 제트 롤 댐핑의 최대값을 산출하였다. 또한 축대칭 압축성 난류 유동에 대한 수치 해석을 통하여 산출한 제트 롤 댐핑값을 비교하였다. Between rolling airframe missile and swirling propulsion jet passing through convergent-divergent nozzle of the rocket motor, occur exchanges of angular momentum which result in the increase of roll speed of the missile. This phenomena in called jet roll damping. In the study jet roll damping was formulated from conservation equation of angular momentum. And the maximum value of the jet roll damping of KPSAM was estimated with assumed swirl velocity distribution at nozzle exit and compared with result of computation of axisymmetric compressible turbulent nozzle flow.

LDV measurements of axial distributions of in-cylinder gas velocities.

Velocity distributions of in-cylinder gas flow in a two cycle uni-flow type engine were measured under motoring conditions by a forward scattered LDV. Measurements were conducted in several planes along the cylinder axis so that the axial distribution and decaying process of swirl velocity in the whole combustion chamber could be investigated. The obtained results are as follows. (1) The initial profile of swirl velocity distribution like solid-body-rotation changes into a flat-top trapezoidal one during the course of the compression and the expansion stroke. (2) A complicated three dimensional flow structure exists in the early compression stroke. (3) The volume mean angular momentum of swirl velocity decays monotonously and maintains about 65% of the initial value when TDC is reached. It shows a similar decaying process in a pancake shaped constant volume bomb after the midway in the compression stroke.

Influence of Induction Swirl and Piston Configuration on Air Flow in a Four-Stroke Model Engine

Measurements of ensemble-averaged mean, r.m.s. and cycle resolved instantaneous swirl velocities, obtained by laser—Doppler anemometry, are reported for the in-cylinder flow in a four-stroke model engine motored at 200 r/min. Variable induction swirl was created by 30° and 60° vanes located in axisymmetric and off-centre intake ports with flat and re-entrant bowl piston configurations. The results showed that the main features of the initial swirl velocity distribution, which are determined by the intake port/valve geometry, persist through the compression stroke. The swirl centre performed in all cases a helical motion whose development was a function of the clearance volume at top dead centre; the weakness of this motion made it susceptible to cyclic variations which were significantly reduced with the re-entrant piston bowl. High induction swirl resulted in lower turbulence intensity at top dead centre of compression, in the flat piston case, and more complex vortex pattern inside the re-entrant piston bowl. The angular momentum decay from inlet valve closure to top dead centre of compression was shown to depend on initial swirl ratio and velocity distribution and calculated to be about 30 and 45 per cent for the flat and re-entrant bowl piston, respectively.

Turbulent swirl with gas—solid flow in cyclone

Two-phase gas—solid flow in cyclone has been investigated to determine the effect of particles on the swirl velocity distribution. With the help of two-phase Navier—Stokes equations, the swirl velocities of the fluid and the particle phases have been evaluated theoretically by numerical schemes. The results highlight the effect of momentum coupling between phases, causing a significant change in the velocity profile with variation of particle size and concentration. The theoretical predictions reasonably agree with experimental results.

The decay of a turbulent swirl in a pipe

This paper presents a linearized theory for the average decay of a tape-induced fully developed turbulent swirl in flow through a pipe. In the Reynolds number range between 104and 105the theoretical analysis was found to be in good agreement with experimental data obtained with water in a 1 in. pipe, provided the eddy diffusivity was chosen appropriately.It was observed that a turbulent swirl decays to about 10–20% of its initial intensity in a distance of about 50 pipe diameters, the decay being more rapid at smaller than at larger Reynolds numbers. The theoretical swirl velocity distribution agreed qualitatively with experimental measurements at distances less than 20 diameters downstream from the outlet of the swirl inducer, but deviated from the experimental results further downstream.