Vortex Tube Research Articles

Vortex bursting and associated twist dynamics on helical vortex tubes and vortex rings

The interaction of opposite-signed twist waves on vortex tubes can lead to vortex bursting, a process where the core expands into a double ring-like structure with strong swirling flows. Previous works have studied vortex bursting on rectilinear vortices by axially perturbing the initial core size to generate the twist waves, and observed largely axisymmetric bursting dynamics. In this work, we numerically study bursting on vortical structures with curved centrelines, analysing the interaction between the centreline dynamics, twist wave generation and propagation, and vortex bursting. We focus on axially perturbed helical vortex tubes with small radius-to-pitch ratios up to $0.0625$ , as well as vortex rings with a large radius-to-core size ratio $10$ , both at a circulation-based Reynolds number $5000$ . The results show that though the initial twist wave propagation speeds are relatively unaffected by the curvature and torsion of the centreline, the bursting process is altered significantly compared with rectilinear vortices. The self-induced rotation of the centreline of the helical tube induces a non-axisymmetric distortion of the bursting structure, which rapidly breaks up the vortex core into small-scale helical structures. A similar destabilization of the bursting structure also occurs on vortex rings. The enstrophy increase and accelerated energy decay associated with bursting are predominantly determined by the twist wave strength, rather than the curvature and torsion of the centreline. Combined, our findings imply that bursting could play an important role in transferring and dissipating energy of vortical structures in wakes, and turbulent flows in general.

An experimental investigation on the effects of the vortex tube material, swirl generator material and the tube length to diameter ratio on vortex tube performance

The current research investigates the effects of the swirl generator material, the tube length to diameter (L/D) ratio, and the vortex tube housing material on its performance. Two vortex tube were designed and constructed using either stainless or brass. In addition to testing different materials for the housing, 5 different materials were examined as potential options for the swirl generator, including stainless steel, brass, polyamide, acrylic and wood. All were having nozzle number of 6. The study encompassed three main areas: examining the impact of various L/D ratios on an entirely stainless vortex tube (ESVT) and an entirely brass vortex tube (EBVT), exploring various swirl generator materials at an optimal L/D ratio for the stainless vortex tube and the brass vortex tube, and investigating the influence of an optimal swirl generator material with varying L/D ratios for the stainless and brass vortex tubes. Operating conditions were controlled for all tests, the natural refrigerant, compressed air was used, the inlet pressure was set to 3.0 bar and the cold mass fraction was varied from 0.40 to 0.90. The results revealed that the performance of the ESVT was greater than the EBVT. The best combination was the polyamide swirl generator and brass vortex tube with an L/D ratio of 19.0. This resulted in the maximum isentropic efficiency of 0.27 at a cold mass fraction of about 0.47.

High-accuracy experimental study of performance characteristics of optimised Ranque-Hilsch vortex tube

In this paper we present high-accuracy experimental measurements of the performance characteristics of an optimised Ranque-Hilsch vortex tube of cylindrical counter-flow design. Although this is a relatively mature research area, the published high-accuracy experimental data with quantified measurement uncertainty is very limited. The purpose is to provide a reference data-set for CFD method validation and calibration. The vortex tube design is a performance-optimum based on existing literature. We characterize the temperature separation, energy separation, efficiency, and coefficients of performance for three inlet pressures (3.0 bar, 5.0 bar and 7.0 bar) and for atmospheric back pressure. Performance characteristics are presented as a function of cold gas mass fraction. The lowest non-dimensional cold-exit temperature (normalised by inlet temperature) was 0.87, the highest coefficient of performance (decrease in enthalpy flux of the cold stream normalized by work needed to compress air to the inlet pressure) was 0.137, and the highest isentropic efficiency (ratio of the actual energy lost by cold stream to energy that would have been lost in an isentropic expansion of the entire inlet stream from the inlet pressure to the cold-exit pressure) was 0.16.

Research on the prediction model of energy separation effect of vortex tube based on trajectory deflection characteristics and its numerical solution method

In this paper, in order to establish the energy separation mechanism of the vortex tube, the hydrodynamic behavior of the compressible fluid in the asymmetric cavity space is investigated, and a numerical model of the trajectory deflection behavior is deduced and established; in order to form the optimal design method of the structural parameters of the vortex tube, the force situation of the fluid microelements entering different regions of the vortex chamber of the vortex tube is analyzed, and the trajectory deflection equations are corrected by combining with the expansion behavior of the fluid and the characterizing equations of vortex strength, transportability, and vortex initiation characteristics are given. The characterization equations of vortex strength, transportability and vortex initiation characteristics are given, and the numerical simulation of their influence parameters is carried out; in order to realize the prediction of the vortex tube performance of a given structure, the multifactor Pearson thermodynamic map is used to correlate and analyze the experimental data of vortex tubes reported publicly in the past years, and the polynomial regression equations are designed and established for the prediction of the vortex tube's energy separation effect and the confidence level and the degree of coincidence of the prediction results are examined. The confidence level and degree of agreement of the prediction results were examined. It is found that: the trajectory deflection motion of the compressible fluid in the asymmetric cavity space is the result of the combined effect of structural air pressure bias and the expansion behavior of the incident fluid; in order to improve the vortex strength in the vortex tube, the vortex initiation chamber space should be as small as possible; the increase of the diameters of the hot-end pipe and the cold-end pipe is conducive to the enhancement of vortex strength, but at the same time, it weakens the vortex transport in the heat pipe; the vortex initiation chamber size has a negative correlation with the hot-end temperature rise, and the inlet fluid pressure has a The negative correlation between the size of the vortex chamber and the temperature rise at the hot end, the positive correlation between the increase of inlet fluid pressure and the resulting temperature rise, and the strong correlation between the inlet fluid pressure and the friction coefficient on the effect of energy separation; the predictive equations for the effect of energy separation obtained by the fitting are in good agreement with the real situation.

Investigation on grinding temperature characteristics of CF/PEEK and material removal mechanism under temperature treatments

Carbon fiber reinforced thermoplastic (CFRTP) composites grinding temperatures could even exceed the glass transition temperature (Tg) of the material due to heat accumulation, combined with the unknown material removal mechanism, resulting in machining defects. To investigate the grinding temperature distribution and maximum temperatures of carbon fiber-reinforced poly-ether-ether-ketone (CF/PEEK) composites, as a typical kind of CFRTP, an analytical temperature model considering the anisotropy was proposed based on the moving heat source theory, verified by the experimental results measured by the infrared camera. Further, the material removal mechanism under temperature treatments (below and above Tg) was also studied. In high temperatures (above Tg), there were many defects on surfaces after grinding, including resin smearing, severe deflection, fiber distortion, and grinding wheel clogging. Therefore, to reduce the grinding temperature below Tg, the vortex tube cooling-assisted grinding method was proposed in the research. The proposed method could reduce the grinding temperature in the grinding area, suppress resin smearing, improve the surface quality, enhance the elastic modulus and nano-hardness of the workpiece, and reduce the clogging of grinding wheels. This study provided a better understanding of the CF/PEEK grinding temperature characteristics and suggested a method to improve the grinding quality.

RANQUE-HILSCH VORTEX TUBE AS AN EDUCATIONAL TOOL FOR CLASSICAL THERMODYNAMICS TEACHING

A vortex or Ranque-Hilsch tube is a moving parts-free device that splits a compressed air stream into a cold and a hot stream at its two extremities. Although there exist some theoretical approaches based on internal shock and expansion waves as well as Maxwell velocity distribution, a final word on the phenomenon to explain the thermal energy splitting has not been reached yet. Nevertheless, from the classical Thermodynamics point-of-view, the conservation laws of mass and energy along with the Second Law validation applied to a control volume enveloping the vortex must be fulfilled. Consequently, such a simple device may be an outstanding tool for hands-on laboratory teaching of engineering Thermodynamics. In accordance with that, an educational laboratory test rig was conceived to carry out experiments to demonstrate the fundamental laws: mass and energy conservations, and the Second Law constraint. As a secondary goal, students can be acquainted with flow, pressure, and temperature measuring techniques, along with obtaining thermodynamic properties, computing, and data-reducing procedure as part of the testing as well. In addition, the coefficient of performance in refrigeration and heat pump operation modes can be obtained and a proper discussion of the vortex tube working principle can be fostered.

Experimental study on the influence of inlet pressure on the flow parameters at the reverse flow boundary of vortex tube and its relation with energy separation performance

The performance of the vortex tube (also known as the Ranque-Hilsch tube) is significantly influenced by the inlet pressure and the internal flow processes, which can be categorized into two distinct flows: the center and the outer flow. The reverse flow boundary, acting as the interface between the two flows, plays a crucial role in energy separation. However, the research on the location of the reverse flow boundary and the associated flow parameters and energy transfer at this boundary are still insufficient. Therefore, this research employs the measurement method of interpolation probe to analyze the distribution of the reverse flow boundary and the specific flow parameters at this boundary. These parameters include static pressure gradient, angular velocity, and static temperature gradient, which substantially impact energy separation. A qualitative analysis of the energy transfer process in the vortex tube by examining mass flow in the reverse area and tangential and axial velocities are further delved. This analysis covers momentum transfer, heat transfer, and turbulent heat transfer processes resulting from the compression and expansion processes. The findings provide a research direction for exploring the energy separation performance of vortex tubes.

Numerical simulations and local entropy generation in a two-phase transcritical carbon dioxide Ranque-Hilsch vortex tube

The Ranque-Hilsch vortex tube arouses a renewed interest as a robust expansion device able to produce thermal energy separation. However, its two-phase transcritical CO2 operation remains unclear. In this work, 3D computational fluid dynamics simulations are performed using the open-source SU2 solver which key features are the implicit time integration and the real gas density-based formulation. The homogeneous equilibrium two-phase model is coupled with both the k−ω shear stress transport and the standard k−ϵ turbulence closures while a fast tabulated version of the Span and Wagner equation of state enables to compute the CO2 properties. First, the validation is performed on pressure measurements, condensation onset positions and visualizations in a transcritical CO2 nozzle available in the literature. Then, the vortex tube transcritical CO2 temperature, energy and phase separations are thoroughly investigated as well as the integral and local entropy generations due to viscous and heat dissipations. The results reveal that the temperature separation is produced below the inlet temperature at both outlets due to real gas effects. It is also shown that the energy separation is reversed as well as the available vortex tube outlet powers for heating and cooling purposes. Furthermore, higher irreversibility due to fluctuating components is unveiled near the vortex tube sharp angles at high cold mass fraction and high inlet operating pressure. Throughout this analysis, compelling arguments in favor of the friction theory for the energy separation phenomenon are also disclosed. Overall, the present work gives useful operation guidelines and sheds light on the complex phenomena at play in a Ranque-Hilsch vortex tube for transcritical CO2 heat pumps.

A Comparative Study of the Mode-Decomposed Characteristics of the Asymmetricity of a Vortex Rope with Flow Rate Variation

In hydro turbines, the draft tube vortex rope is one of the most crucial impact factors causing pressure pulsation and vibration. It is affected by operating conditions due to differences in the flow rate and state and can be symmetric or asymmetric along the rotational direction. It may influence the stability of draft tube flow. To achieve a better understanding, in this work, dynamic mode decomposition is used in a draft tube case study of a simplification of a vortex rope. As the flow rate increases, the shape of the vortex rope becomes clear, and the flow rotation becomes more significant as the inlet flow rate increases. Dynamic mode decomposition was used to determine the relative frequencies, which were 0 (averaged), 0.7 times, and 1.4 times the features of the reference frequency. As the inlet flow rate increases, the order of high-energy modes and their influence on the vortex rope gradually increase, and this characteristic is exhibited further downstream of the draft tube. When the inlet flow rate is low, the impact of mode noise is greater. As the flow velocity increases, the noise weakens and the rotation mode becomes more apparent. Identifying the mode of the vortex flow helps extract characteristics of the vortex rope flow under different operating conditions, providing a richer data-driven basis for an in-depth analysis of the impact of operating conditions on the flow stability of a draft tube.

Numerical Study of the Gas–Solid Separation Performance of Axial Flow Cyclone Separators

Cyclone separators, which have a high separation performance, play a crucial role in mitigating the occurrence of dust explosion incidents. This study aims to improve the performance of an axial cyclone separator using the results of simulations employing the RNG k-ε model together with a user-defined function to simulate the wall collision process. The effectiveness of various structural modifications to the vortex tube has been addressed. Specifically, we found that increasing the number of blades, reducing the blade exit angle, and adopting L-shaped blades increase separation efficiency. Additionally, enlarging the guide vane and exhaust pipe diameters, as well as increasing the exhaust pipe inclination angle, contribute to an improved separation performance due to the developed tangential velocity and vortex cores. However, it also increases the pressure drop losses due to the increase in the turbulence pulsation entropy and the wall entropy, while the time-averaged entropy is found to be less significant. As a result, our study sheds light on the flow characteristics, the gas–solid separation process, and the energy loss mechanism in the cyclone separator.

Numerical study on how advection delays and removes singularity formation in the Navier–Stokes equations

We numerically study a distorted version of the Euler and Navier–Stokes equations, which are obtained by depleting the advection term systematically. It is known that in the inviscid case some solutions blow up in finite time when advection is totally discarded, Constantin (1986 Commun. Math. Phys. 104 311–26). Taking a pair of orthogonally offset vortex tubes and the Taylor–Green vortex as initial data, we show the following. (1) Blowup persists even with viscosity when advection is discarded, and (2) for small viscosity, the time of blowup increases logarithmically as we reinstate advection using a continuous parameter, which would be consistent with the regularity of the Navier–Stokes equations. A tiny mismatch in the coefficient of the advection term, as minute as parts per trillion, throws the system out of compactness and leads to blowup.

Structure and role of the pressure Hessian in regions of strong vorticity in turbulence

Amplification of velocity gradients, a key feature of turbulent flows, is affected by the non-local character of the incompressible fluid equations expressed by the second derivative (Hessian) of the pressure field. By analysing the structure of the flow in regions where the vorticity is the highest, we propose an approximate expression for the pressure Hessian in terms of the local vorticity, consistent with the existence of intense vortex tubes. Contrary to the often used simplification of an isotropic form for the pressure Hessian, which in effect inhibits vortex stretching, the proposed approximate form of the pressure Hessian enables much stronger vortex stretching. The prediction of the approximation proposed here is validated with results of direct numerical simulations of turbulent flows.

Vortex model of plane turbulent air flows in channels

We present a theoretical model of plane turbulent flows based on the previously proposed equations, which take into account both the longitudinal motion and the vortex tube rotation. Using the simple model of eddy viscosity, we obtain the analytical expressions for the mean velocity profiles of stationary turbulent flows. In particular, we consider the near-wall flow over a flat plate in a wind tunnel as well as Couette and Poiseuille flows in rectangular channels. In all these cases, the calculated velocity profiles are in good agreement with experimental data and results of direct numerical simulations.

Energy, Exergy, Exergoeconomic Analysis, and Optimization in a Natural Gas Decompression Station with a Vortex Tube and Geothermal Preheating

Natural gas stations require a preheating stage to prevent the formation of hydrates inside of them provoked by a sudden decompression process of the natural gas. The preheating process has been investigated to improve efficiency and to reduce costs as well. This work studies the behavior of a natural gas decompression station with a first-stage preheating process using a vortex tube and a geothermal heat exchanger, followed by a second stage involving a water bath heater (heating vat). An energetic, exergetic, and exergoeconomic study has been carried out based on a mathematical model and the theory of exergetic cost, obtaining key thermodynamic and thermoeconomic variables, including exergy flows and equipment costs. A heat flow of 26.41 kW was obtained in the geothermal preheating stage; meanwhile, a 60.43 kW heat flow was obtained in the heating vat. The results showed a saving in station fuel using only 2.046% of the natural gas in the system at the second preheating stage. Also, the system was optimized, obtaining a 15.73% reduction in the decompressed natural gas cost. These findings show the possibility of implementing these systems in zones with many geothermal resources to reach a constant, profitable natural gas supply in areas where a pipeline network does not exist.

Effects of structural parameters on air consumption and mechanical energy characteristics of airflow in the vortex spinning nozzle

Reducing energy consumption during textile production processes has currently become one of the key concerns. In order to design the nozzle of the vortex spinning machine with reduced air consumption, numerical simulation of the airflow in the nozzle is performed to investigate the effect of the length and the inlet diameter of the conical chamber in the intermediate section of the vortex tube on the air consumption and the mechanical energy characteristics of the airflow. A spinning experiment conducted to measure the flow rate and yarn tenacity is adopted to verify the numerical simulation results. The simulation results show that the air consumption of the nozzle is insignificantly affected as the length increases from 7.3 mm to 7.7 mm, while a decreasing trend has been found as the length increases from 7.7 mm to 8.1 mm. As the inlet diameter increases from 4.6 mm to 5.0 mm, the air consumption of the nozzle increases monotonically. The mechanical energy of airflow in the nozzle exhibits a minor difference between cases of lengths of 7.3 mm, 7.5 mm, and 7.7 mm, while it decreases significantly in cases of lengths of 7.9 mm and 8.1 mm. The mechanical energy of airflow in the vortex chamber increases as the inlet diameter increases. The experimental results are consistent with the numerical predictions. This work is expected to provide a reference for the design of the vortex spinning nozzle and an approach to reducing the energy consumption in the yarn production process.

Flow analysis for lateral synthetic jets to remove contaminants from the outer surface of an automobile camera module

A test facility was constructed to investigate the flow characteristics of lateral synthetic jets generated by an actuator composed of a cavity, an orifice and a vibrating piezoelectric disc. Subsequently, 3D unsteady numerical simulations were conducted to analyze the formation of the synthetic jets and their dependence on the height of the orifice exit from the outer surface of the cavity. The time-averaged axial velocity was measured and used to validate the numerical results, and the maximum velocity reached approximately 8 m/s. In this work, it was found that the interaction of the vortex tube generated at the edge of the orifice exit and the outer surface of the cavity has a significant impact on the axial velocity distribution and characteristics of the lateral synthetic jets. Based on the experimental data and the numerical results, an attempt has been made to understand the formation of the synthetic jets and their interaction with the outer surface.

Machine learning-based vorticity evolution and super-resolution of homogeneous isotropic turbulence using wavelet projection

A wavelet-based machine learning method is proposed for predicting the time evolution of homogeneous isotropic turbulence where vortex tubes are preserved. Three-dimensional convolutional neural networks and long short-term memory are trained with a time series of direct numerical simulation (DNS) data of homogeneous isotropic turbulence at the Taylor microscale Reynolds number 92. The predicted results are assessed by using the flow visualization of vorticity and statistics, e.g., probability density functions of vorticity and enstrophy spectra. It is found that the predicted results are in good agreement with DNS results. The small-scale flow topology considering the second and the third invariants of the velocity gradient tensor likewise shows an approximate match. Furthermore, we apply the pre-trained neural networks to coarse-grained vorticity data using super-resolution. It is shown that the super-resolved flow field well agrees with the reference DNS field, and thus small-scale information and vortex tubes are well regenerated.

Contribution of interphase force curl to rigid vorticity transport in water-sand two-phase flow with fine particles

Rigid vorticity transport equation is an effective tool for describing the intuitive vortex evolution characteristics. Compared to single-phase flows, the curl of the interphase force appears as a new source term of this equation under the condition of multiphase flows, which may cause additional contributions. However, the effects of the interaction force on rigid vorticity transport in water-sand two-phase flows with fine particles are still unclear. In this article, taking the Karman vortices induced by a hydrofoil as a typical case, the distributions of rigid vorticity in single-phase flows and two-phase flows were compared, and the dynamics mechanism of the dominant interaction force was analyzed. The following notable results are obtained. Firstly, the drag force can be regarded as the dominant interaction force. Secondly, the effect of the drag force on a vortex tube is mainly manifested as inducing normal strain and the contribution is relatively low. Thirdly, there are only slight differences in the waveform, amplitude, frequency of rigid vorticity and apparent vortical structures between the single-phase flows and the fine-particle two-phase flows. These new findings are helpful for understanding the vortex evolution in water-sand two-phase flows with fine particles.

Numerical analysis and an approach for optimization of the Ranque–Hilsch vortex tube for a compressible flow

The Ranque–Hilsch vortex tube is a fluidic device well-known for its energy separation capability. In the present study, the swirling flow inside the vortex tube are computational predicted and analyzed for the optimization purpose. The numerical analysis was conducted on a previously available vortex tube design and the results are well validated. After a thorough comparison, the Re-Normalization Group K-epsilon turbulence model is choose for a reliable computation of the vortex tube flow field. Effects of the inlet compressed gas properties shows a vital increment in the energy separation until the critical condition occurs in vortex tube. At the critical condition, the increase in the inlet pressure ratio result in the loss of swirl momentum through the hot exit rather than increasing the thermal separation. Analyzing the results, the optimal vortex tube dimensions such as radius and length are predicted to reduce the loss in kinetic energy. The graphical optimization method proposed by the parametric study has to be validated by reliable experimental studies.

Numerical analysis for the thermal performance and flow separation in the vortex tube with different design of flow control valve

Numerical analysis for the thermal performance and flow separation in the vortex tube with different design of flow control valve