Vortex Tube (VT) is a simple device having no moving mechanical parts, in which compressed gas at high pressure is injected through one or more tangential nozzles into a vortex chamber resulting in the separation of the inlet flow into two low pressure streams. One of the streams is the peripheral flow that is warmer than the inlet stream while the other is the central (core) flow that is colder than the inlet stream. This separation of the inlet flow into high and low temperature streams is known as temperature or energy separation. It is suggested by many investigators that compressed air of few atmospheres pressure and at room temperature can produce temperatures as high as +200ºC at the hot end (peripheral flow exit) and as low as -50ºC at the cold end (core flow exit) of the VT. Though VTs have large potential for simple heating and cooling applications, the mechanism of energy separation is not clear so far. Based on their studies, many investigators have suggested various theories, different from each other, but having specific lacunas and is an unresolved issue. Also, till date, experimental and industrial designs of the VTs are based purely on empirical correlations. Apart from heating and cooling applications, VTs can also be used for separation of binary gas mixtures and separation of oxygen from two-phase precooled air stream. The conceptual futuristic cryogenic launch vehicle designs are being attempted with in-flight liquid oxygen (LOX) collection system that significantly improves the pay load fraction. Vortex tube technology is one of the few promising technologies for futuristic in-flight LOX separation based launch vehicles. This technology has significant advantages over its counterparts as it is a simple, compact and light weight, and most importantly have no moving parts and unaffected by gravity and orientation. In order that VTs become an acceptable technology for in-flight LOX separation system, it is necessary to achieve minimum oxygen purity of 90% with more than 60% yield (separation efficiency) for the oxygen enriched stream in the VT. A survey of the available open literature has shown very little reported details, in particular, on achieving the required specifications for in-flight LOX separation systems. Till date, the highest LOX purity of 60% with 40% separation efficiency has been reported with VT technology. In view of the above mentioned facts, the work carried out has been focused on to: • Optimize the critical parameters of the VT to achieve maximum energy separation by CFD and experimental studies. • Understand the flow behaviour in the VT by estimating the velocity, temperature and pressure profiles at various locations in the VT and validation of secondary circulation flow and its effect on the performance of energy separation in VT. • Estimation of the energy transfer between the core and the peripheral layers of fluid flow in VT by analytical and CFD methods to propose the most appropriate mechanism of energy separation in VT. • Design and development of a dedicated experimental setup for both energy separation and LOX separation studies in VTs. • Design and fabrication of straight and conical VTs and experimental programme on energy separation and LOX separation. • Development of the VT air separation technology to achieve the required specifications of in-flight LOX separation system for futuristic launch vehicles. With these specific objectives and motivations, the total work was carried out with the following planned and sequential steps: • The first step was the CFD modeling of the VT with the available CFD software (Star-CD) and obtain the energy separation phenomena for a 12mm diameter VT. After gaining sufficient confidence level, optimization of the critical parameters like the air injection nozzle profile, number of nozzles, cold end orifice diameter dc, length to diameter (L/D) ratio, hot gas fraction etc of the VT was carried out through CFD and experimental studies. • The studies show that 6 convergent nozzles perform better in comparison to other configurations like circular helical, rectangular helical, 2 convergent and 6 straight nozzles. The studies also show that cold end orifice diameter (dc) plays an important role on energy separation and bring out the existence of secondary circulation flow with improper design of cold end orifice diameter. Through our studies, the effect of cold end diameter on the secondary circulation flow has been evaluated for the first time. Also, the mechanism of energy transfer in VT based on heat pump mechanism enabled by secondary circulation flow as suggested by some investigators has been evaluated in our studies. The studies show that cold end orifice diameter dc = 7mm is optimum for 12mm diameter VT, which matches fairly with the correlations given by other investigators. The studies confirms that CFD modeling carried out in this work is capable of selecting the correct dc value for a VT, without resorting to the empirical correlations as a design guide or a laborious experimental programme. • Through the CFD and experimental studies on different length to diameter (L/D) ratios and hot gas fractions, maximum hot gas temperature of 391K was obtained for L/D = 30 with hot gas fraction of 12-15 % and minimum cold gas temperature of 267K for L/D = 35 was obtained for cold gas fraction ≈ 60% (lowest cold gas fraction possible with the present experimental system). • CFD analysis has been carried out to investigate the variation of static and total temperatures, static and total pressures as well as the velocity components of the particles as it progresses in the flow field, starting from the entry through the nozzles to the exit of the VT by tracking the particles to understand the flow phenomenon and energy transfer mechanism inside the VT. The studies indicate that the mechanism of energy transfer from the core flow to the peripheral flow in VT is predominantly occurs by the tangential shear work. Thus the investigations reported in the thesis have given a clear understanding of the contributing mechanism for energy separation in VT, which has been an unresolved issue for long time. The net energy transfer between the core and the peripheral fluid has been calculated analytically and compared with the values obtained by CFD model for VTs of L/D ratios equal to 10 and 30. The net energy transfer by analytical and CFD model for VT with L/D = 10 is 159.87W and 154.2W respectively whereas the net energy transfer by analytical and CFD model for VT with L/D = 30 is 199.87W and 192.3W respectively. The results show that CFD results are in very good agreement with the analytical results and CFD can be used as a tool for optimization of the critical parameters and to analyze the flow parameters and heat transfer analysis for VTs. Also, the net energy transfer between the core and peripheral fluids calculated analytically matches very well with that of the net energy transfer by CFD analysis, without considering the effect of acoustic streaming. Thus acoustic streaming may not be the mechanism of energy separation in VT as suggested by some investigators. • By optimizing the critical parameters of the 12mm diameter straight VT through CFD and experimental studies, LOX separation studies have been carried out using both straight and conical VTs of dc = 7mm and of different L/D ratios for high LOX purity and separation efficiency. It is observed that conical (3º divergence) VTs perform better as compared to straight VTs for LOX separation whereas straight VTs perform better for energy separation. The better performance of conical VT as compared to straight VTs can be attributed to its increased surface area for condensation-evaporation phenomenon of oxygen and nitrogen molecules. Experimental studies have been conducted to evaluate the influence of the inlet pressure and the inlet temperature (liquid fraction) on LOX purity. Studies indicate that for achieving high LOX purity for the studied experimental system, the inlet pressure is to be in the range of 6-6.5bar and there exists a very narrow band of inlet temperature zone in which high LOX purity can be achieved. Experimental studies on VTs show that VT can be optimized suitably either for high LOX purity with low separation efficiency or low LOX purity with high separation efficiency by adjusting the hot end mass fraction accordingly. It is also observed that it is not possible to obtain both high purity and high separation efficiency simultaneously with the single VT. Staging approach has to be adapted to achieve higher LOX purity with higher separation efficiency. By staging the VTs, the enriched air stream (hot end outlet flow) from the first stage of VTs is introduced to the inlet of the second stage of VTs. Experimental studies have been conducted to evaluate the design parameters on staging of VTs. LOX purity of 48% with 89% separation efficiency has been achieved for conical first stage VT of L/D = 25. LOX purity of about 94% with separation efficiency of 84% has been achieved for 50% oxygen content at the inlet of the second stage VT. Similarly, LOX purity of 96% with separation efficiency of 73.5% has been achieved for 60% oxygen content at the inlet of the VT. This is the highest LOX purity and separation efficiency reported so far indicating that, conical VT of optimized diameter, L/D ratio and orifice diameter can yield the hot end flow very close to the target value of futuristic in-flight LOX separation based launch vehicles. The present investigation has focused the optimization of the critical parameters of VTs through CFD and experimental studies. It has also given an insight to the mechanism of energy transfer between the core and peripheral flow in VT by evaluating two of the existing theories on mechanism of energy transfer in VT. The studies also highlighted the fact that custom designed and precision fabricated VTs can be very useful for obtaining maximum / minimum temperatures of fluid flow as well as LOX separation with high purity and high separation efficiency needed for futuristic in-flight LOX separation based space launch vehicles.

An isolated wing-tip vortex from a square-tipped NACA 0012 wing at an angle of attack of 5 degrees was studied in a water tunnel at a chord based Reynolds number of approximately 24000. Measurements were taken using stereo particle image velocimetry at three measurement planes downstream of the wing under each of three freestream turbulence conditions. The amplitude of wandering of the vortex axis increased with increasing distance downstream of the wing and with increasing freestream turbulence intensity. The magnitude of the peak azimuthal velocity decreased with increasing distance from the wing as well as with increases in the freestream turbulence intensity. The streamwise velocity in the vortex core was less than the freestream velocity in all cases. Time resolved histories of the instantaneous waveform shape and location of the vortex axis were determined from sequences of images of fluorescent dye released from the wing.

Neste trabalho simulou-se o escoamento do fluxo de ar em um tubo, com um anteparo de formato triangular com arestas cortantes, posicionado no centro do tubo. O objetivo do estudo é a análise do comportamento do número de Strouhal em função do número de Reynolds. Para isto, foi utilizada a técnica da análise tempo-freqüência, baseada na transformada de Fourier e na transformada de Gabor. Os ensaios foram realizados com o fluxo com velocidades médias de escoamento de 3 a 10 m/s, sendo utilizado um sensor de pressão tipo piezo-resistivo para a detecção da flutuação de pressão ocasionada pelo desprendimento e formação dos vórtices. Os ensaios foram realizados em cinco etapas com o objetivo de se verificar a influência dos seguintes parâmetros na coleta de sinais e no fenômeno: ruído da rede elétrica; influência do anteparo e do ruído proveniente do escoamento do fluxo de ar; número de pontos da amostragem na coleta dos dados; do comprimento da tubulação; e posicionamento do sensor. Pode-se observar, a sensibilidade do sistema de medição através do ensaio realizado sem o anteparo, sendo verificada a influência do ruído do escoamento de ar pelo tubo; pode-se observar também uma pequena interferência do ruído da rede elétrica predominantemente para velocidades abaixo de 3 m/s. Apesar das influências citadas, e utilizando a transformada de Gabor para análise dos sinais, observou-se um sinal mais intenso na freqüência dos vórtices para as velocidades de escoamento, podendo-se comprovar que o número de Strouhal permanece quase constante e é independente do número de Reynolds, devendo-se ressaltar que esta conclusão é valida para números de Reynolds compreendidos na faixa de 3000 a 100000. No experimento obteve-se um fator de sensibilidade (freqüência vórtices/velocidade média) de 8,2 Hz/m/s, e número de Strouhal médio de 0,196. / This work concerns the simulation of an air flux through a pipe with a triangular bluff body positioned inside it. In order to study the behavior of the Strouhal number in function of the Reynolds number. For this, the time-frequency analysis technique was used, based on Fourier transform and the Gabor transform. The experiments were carried out with an air flux velocity ranging from 3 to 10 m/s and using a piezoresistive pressure sensor to detect pressure fluctuations caused by the shedding and vortex formation. The experimental procedures were divided in five stages to make it possible to verify the influence of the following parameters in the signal data acquisition: electric network noise, the bluff body presence and the noise generated due to its presence, number of sampling data points, tubing length and sensor positioning. The sensitivity of the experiment could be observed testing the air flowing with no bluff body inside the pipe. Thus, it was possible to investigate the influence of the noise generated due to this flux limiting body. It could be also observed, mainly at 3 m/s or less, the noise generated due to the electric network. Despite the listed influences, and with the use of the Gabor transform, a more intense signal on the vortex frequency for the flow velocity was observed, showing that the Strouhal number remains almost constant and is independent of the Reynolds number. It is important to recall that this conclusion is valid for Reynolds numbers between 3000 and 100000. In the experiments the factor of sensitivity (vortex frequency/mean velocity) obtained was 8,2 Hz/m/s and the mean Strouhal number 0,196.

"Optical vortices are ubiquitous features of electromagnetic radiation that are often described as a destructive null in a beam of coherent light. Optical vortices may be created by a variety of different methods, one of which is by the use of a diffractive vortex mask, which is a plate of glass that has been etched in a spiral staircase pattern such that the thickness of the mask varies harmonically in the azimuthal direction. Light passing through the mask gains an azimuthal variation in phase due to the index mismatch between the glass substrate and the surrounding medium and thus an optical vortex is created. There is an implicit assumption that the light is spatially coherent, or in other words, that there is a definite phase relationship between each point in the beam. Optical vortices are not believed to occur in completely incoherent light where the term “phase” no longer holds any meaning. Optical vortices are also poorly understood in partially coherent light where statistics must be used to quantify the phase. The purpose of the research presented in this thesis was to determine how spatial coherence affects the transmission properties of the vortex phase mask. This research enabled us to create a coherence filtering technique based upon the vortex diffractive mask. In this dissertation I will demonstrate the usefulness of this filtering technique in two specific applications. First in the detection of forward-scattered light, where the un-scattered probe beam may blind a detector making detection of the scattered light extremely difficult. Second, in the enhanced resolution of two nearby objects, where the signal from one object may be lost in the glare of a brighter companion. This filtering technique has a wide field of possible applications including the detection of extra-solar planets, the detection of defects in laser optics, and improved methods in optical tomography."

Fluid dynamics considers the physics of liquids and gases. This is a branch of classical physics and is totally based on Newton's laws of motion. Nevertheless, the equation of fluid motion, Navier-Stokes equation, becomes very complicated to solve even for very simple configurations. This thesis treats mainly analytical vortex solutions to Navier-Stokes equations. Vorticity is usually concentrated to smaller regions of the flow, sometimes isolated objects, called vortices. If one are able to describe vortex structures exactly, important information about the flow properties are obtained. Initially, the modeling of a conical vortex geometry is considered. The results are compared with wind-tunnel measurements, which have been analyzed in detail. The conical vortex is a very interesting phenomenaon for building engineers because it is responsible for very low pressures on buildings with flat roofs. Secondly, a suggested analytical solution to Navier-Stokes equation for internal flows is presented. This is based on physical argumentation concerning the vorticity production at solid boundaries. Also, to obtain the desired result, Navier-Stokes equation is reformulated and integrated. In addition, a model for required information of vorticity production at boundaries is proposed. The last part of the thesis concerns the examples of vortex models in 2-D and 3-D. In both cases, analysis of the Navier-Stokes equation, leads to the opportunity to construct linear solutions. The 2-D studies are, by the use of diffusive elementary vortices, describing experimentally observed vortex statistics and turbulent energy spectrums in stratified systems and in soapfilms. Finally, in the 3-D analysis, three examples of recent experimentally observed vortex objects are reproduced theoretically. First, coherent structures in a pipe flow is modeled. These vortex structures in the pipe are of interest since they appear for Re in the range where transition to turbulence is expected. The second example considers the motion in a viscous vortex ring. The model, with diffusive properties, describes the experimentally measured velocity field as well as the turbulent energy spectrum. Finally, a streched spiral vortex is analysed. A rather general vortex model that has many degrees of freedom is proposed, which also may be applied in other configurations.

Boundary layer separation is an unwanted phenomenon in most technical applications, as for instance on airplane wings, ground vehicles and in internal flow systems. If separation occurs, it causes loss of lift, higher drag and energy losses. It is thus essential to develop methods to eliminate or delay separation.In the present experimental work streamwise vortices are introduced in turbulent boundary layers to transport higher momentum fluid towards the wall. This enables the boundary layer to stay attached at  larger pressure gradients. First the adverse pressure gradient (APG) separation bubbles that are to be eliminated are studied. It is shown that, independent of pressure gradient, the mean velocity defect profiles are self-similar when the scaling proposed by Zagarola and Smits is applied to the data. Then vortex pairs and arrays of vortices of different initial strength are studied in zero pressure gradient (ZPG). Vane-type vortex generators (VGs) are used to generate counter-rotating vortex pairs, and it is shown that the vortex core trajectories scale with the VG height h and the spanwise spacing of the blades. Also the streamwise evolution of the turbulent quantities scale with h. As the vortices are convected downstream they seem to move towards a equidistant state, where the distance from the vortex centres to the wall is half the spanwise distance between two vortices. Yawing the VGs up to 20° do not change the generated circulation of a VG pair. After the ZPG measurements, the VGs where applied in the APG mentioned above. It is shown that that the circulation needed to eliminate separation is nearly independent of the pressure gradient and that the streamwise position of the VG array relative to the separated region is not critical to the control effect. In a similar APG jet vortex generators (VGJs) are shown to as effective as the passive VGs. The ratio VR of jet velocity and test section inlet velocity is varied and a control effectiveness optimum is found for VR=5. At 40° yaw the VGJs have only lost approximately 20% of the control effect. For pulsed VGJs the pulsing frequency, the duty cycle and VR were varied. It was shown that to achieve maximum control effect the injected mass flow rate should be as large as possible, within an optimal range of jet VRs. For a given injected mass flow rate, the important parameter was shown to be the injection time t1. A non-dimensional injection time is defined as t1+ = t1Ujet/d, where d is the jet orifice diameter. Here, the optimal  t1+ was 100-200. / QC 20100825

The present study describes the flow characteristics of swirling flows induced by twisted tape inserts in circular pipes. The study is focused on the secondary flow which is investigated experimentally and with numerical models. The results are expected to improve the paper manufacturing process by identifying and removing the detrimental secondary flow. Experimental tests show for the first time the existence of two co-rotating helical vortices superimposed over the main swirling flow, downstream of twisted tapes. The close proximity of the two co-rotating vortices creates a local counter-rotating flow at the pipe centerline. The flow is analyzed using LDV measurements and high speed camera visualization with fine air bubbles seeding which confirm that the helical vortices are stable. After extracting the characteristic tangential velocity profiles of the main vortex and of the two secondary vortices, it was observed that the maximum tangential velocity of all three vortices is the same, approximately half of the bulk velocity. The winding of the helical vortices is in the swirl direction and the pitch of the helical vortices is found to be independent of the inlet velocity. The experimental findings are confirmed by numerical simulations. The numerical results show that the helical vortices originate inside the swirler and evolve from single co-rotating vortices on each side of the tape. The flow characteristics are analyzed in detail. Swirlers with multiple twists and multiple chambers are shown to have less stable secondary motion and could be employed in applications were the secondary motion is detrimental.

Neste trabalho simulou-se o escoamento do fluxo de ar em um tubo, com um anteparo de formato triangular com arestas cortantes, posicionado no centro do tubo. O objetivo do estudo é a análise do comportamento do número de Strouhal em função do número de Reynolds. Para isto, foi utilizada a técnica da análise tempo-freqüência, baseada na transformada de Fourier e na transformada de Gabor. Os ensaios foram realizados com o fluxo com velocidades médias de escoamento de 3 a 10 m/s, sendo utilizado um sensor de pressão tipo piezo-resistivo para a detecção da flutuação de pressão ocasionada pelo desprendimento e formação dos vórtices. Os ensaios foram realizados em cinco etapas com o objetivo de se verificar a influência dos seguintes parâmetros na coleta de sinais e no fenômeno: ruído da rede elétrica; influência do anteparo e do ruído proveniente do escoamento do fluxo de ar; número de pontos da amostragem na coleta dos dados; do comprimento da tubulação; e posicionamento do sensor. Pode-se observar, a sensibilidade do sistema de medição através do ensaio realizado sem o anteparo, sendo verificada a influência do ruído do escoamento de ar pelo tubo; pode-se observar também uma pequena interferência do ruído da rede elétrica predominantemente para velocidades abaixo de 3 m/s. Apesar das influências citadas, e utilizando a transformada de Gabor para análise dos sinais, observou-se um sinal mais intenso na freqüência dos vórtices para as velocidades de escoamento, podendo-se comprovar que o número de Strouhal permanece quase constante e é independente do número de Reynolds, devendo-se ressaltar que esta conclusão é valida para números de Reynolds compreendidos na faixa de 3000 a 100000. No experimento obteve-se um fator de sensibilidade (freqüência vórtices/velocidade média) de 8,2 Hz/m/s, e número de Strouhal médio de 0,196. / This work concerns the simulation of an air flux through a pipe with a triangular bluff body positioned inside it. In order to study the behavior of the Strouhal number in function of the Reynolds number. For this, the time-frequency analysis technique was used, based on Fourier transform and the Gabor transform. The experiments were carried out with an air flux velocity ranging from 3 to 10 m/s and using a piezoresistive pressure sensor to detect pressure fluctuations caused by the shedding and vortex formation. The experimental procedures were divided in five stages to make it possible to verify the influence of the following parameters in the signal data acquisition: electric network noise, the bluff body presence and the noise generated due to its presence, number of sampling data points, tubing length and sensor positioning. The sensitivity of the experiment could be observed testing the air flowing with no bluff body inside the pipe. Thus, it was possible to investigate the influence of the noise generated due to this flux limiting body. It could be also observed, mainly at 3 m/s or less, the noise generated due to the electric network. Despite the listed influences, and with the use of the Gabor transform, a more intense signal on the vortex frequency for the flow velocity was observed, showing that the Strouhal number remains almost constant and is independent of the Reynolds number. It is important to recall that this conclusion is valid for Reynolds numbers between 3000 and 100000. In the experiments the factor of sensitivity (vortex frequency/mean velocity) obtained was 8,2 Hz/m/s and the mean Strouhal number 0,196.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Zhongquan Zheng / In this study, a vortex particle method is used to simulate incompressible vortical flows, specifically aircraft wake vortices. This is particularly suitable for a wake vortex system that is slowly varying in the axial direction and has a high Reynolds number and low Mach number. The flow field, in the form of vorticity, is employed as the source in the far-field acoustic calculation using a vortex sound formula that enables computation of acoustic signals radiated from an approximated incompressible flow field. In a two-dimensional vortex system, the stretching effect in the axial direction is neglected. The purpose of this study is to focus on vortex core behaviors. A numerical simulation is performed in a more realistic wake consisting of a counter-rotating vortex pair with inviscid ground effects and shear flows. A Kirchhoff spinning-core vortex model is thus used as a starting point. In a vortex system with multiple vortices, such as a complicated aircraft vortex wake vortices, the sound emission frequency of the unsteady vortex core is subjected to change because of interactions between multiple vortices. The behaviors of the influence, indicated by the ratio between the core size and the distance of the vortices, are investigated as well as the underlining vortex core dynamic mechanisms. Cases of co-rotating vortices and a multiple-vortex system composed of two counter-rotating vortex pairs are studied for applications to aircraft wake vortex sound. In three-dimensional vortices, sinusoidal instabilities, which occur in the axial direction at various length scales, result in significant flow structure changes in these vortices, and thus influence their radiated acoustic signals. Cases of vortex rings and a pair of counter-rotating vortices are studied when they are undergoing both long-wave and short-wave instabilities. Both inviscid and viscous interactions are considered and the effects of turbulence are simulated using sub-grid-scale models. A higher peak frequency than the Kirchhoff frequency appears due to the straining field caused by mutual perturbation, under both long-wave and short-wave instabilities. Vortices with the initial core vorticity of the Gaussian distribution and the elliptic distribution are also studied.

This work deals with study of swirling flows where the spiral vortical structure appears. The main relation is to flow seen in the draft tube cone of hydraulic turbines operated out of the design point (i.e. best efficiency point). In this cases large coherent vortex structure (vortex rope) appears and consequently high pressure pulsations are propagated to the whole machine system leading to possible restriction of turbine operation. This flow features are consequence of flow instability called vortex breakdown in case of Francis turbine operated at part load (flow rate lower than optimal one). The present study is carried out using simplified device of swirl generator in order to access similar flow conditions as can be found in real hydraulic turbines. Both the dynamic and dissipation effect of spiral vortex breakdown are investigated. The first part of thesis deals with spiral form of vortex breakdown. The experimentally measured velocity profiles (LDA) and wall static pressures are correlated with numerical simulations carried out using open-source CFD package OpenFOAM 2.2.2. The high speed camera recording of cavitating vortex core is used to obtain image ensemble for further post-processing. The dissipation effect of spiral vortex structure is in detail discussed based on computed flow fields. The second part of thesis is dedicated to the application of POD decomposition to the study of spatio-temporal features of spiral vortex dynamics. Firstly the POD is applied to the both the experimentally obtained image ensemble of cavitating vortex and numerically computed static pressure fields. Secondly the comprehensive analysis of spiral vortex mitigation effect by the axial water jet is analyzed. The collaborative study employing the swirl generator apparatus designed by the researchers from Politehnica University of Timisoara in Romania is performed and changes in spatio-temporal vortex dynamic are studied. In this study the numerical data (in a form of three-dimensional pressure and velocity fields) are obtained using commercial CFD software ANSYS Fluent R14.