There are two coupled primary objectives for this study of buoyancy-driven turbulence. The first objective is to create a new diagnostic for collection of measurements to capture the physics of Rayleigh-Taylor (RT) mixing. The second objective is to use the new diagnostic to specifically elucidate the physics of large Atwood number, ( )( )2 1 2 1 / ρ ρ ρ ρ + − = t A , RT mixing. Both of these objectives have been satisfied through the development of a new hot-wire diagnostic to study buoyancy-driven turbulence in a statistically steady gas channel of helium and air ( 6 . 0 03 . 0 ≤ ≤ t A ). The capability of the diagnostic to simultaneously and instantaneously measure turbulent velocity and density fluctuations allows for a unique investigation into the dynamics of Rayleigh-Taylor mixing layers at large At, through measurements of turbulence and mixing statistics. The new hot-wire diagnostic uses temperature as a fluid marker for helium and air, which is possible due to the Lewis number ~ 1 (Le = ratio of thermal diffusivity to mass diffusivity) for helium and air, and the new diagnostic has been validated in an At = 0.03 mixing layer. The energy density spectrum of v′ ′ ρ , measured experimentally for the first time in RT mixing, is found to closely follow the energy distribution of v′ , up to the Reynolds numbers investigated ( ( ) mix t h gA h υ 6 2 Re 2 / 3 = ~ 1450). Large At experiments, with At = 0.6, have also been achieved for the first time in a miscible RT mixing layer. An asymmetric penetration of the bubbles (rising fluid) and spikes (falling fluid) has been observed, resulting in measured self similar growth parameters αb = 0.060 and αs = 0.088 for the bubbles and spikes, respectively. The first experimental measurements of turbulent velocity and density fluctuations for the large At case, show a strong similarity to lower At behaviors when normalized. However conditional statistics, which separate the bubble (light fluid) and spike (heavy fluid) dynamics, has highlighted differences in v′ ′ ρ and rms v′ in the bubbles and spikes. Larger values of v′ ′ ρ and rms v′ were found in the downward falling spikes, which is consistent with the larger growth rates and momentum of the spikes compared to the bubbles. These conditional statistics are a first in RT driven turbulence.

<p>Despite its importance in various industrial applications there is still a lack of experimental studies on the dynamic and thermal field of swirling jets in the near-field region. The present study is an attempt to close this lack and provide new insights on the effect of rotation on the turbulent mixing of a <i>passive scalar</i>, on turbulence (joint) statistics as well as the turbulence structure.</p><p>Swirl is known to increase the spreading of free turbulent jets and hence to entrain more ambient fluid. Contrary to previous experiments, which leave traces of the swirl generating method especially in the near-field, the swirl was imparted by discharging a slightly heated air flow from an axially rotating and thermally insulated pipe (6 m long, diameter 60 mm). This gives well-defined axisymmetric streamwise and azimuthal velocity distributions as well as a well-defined temperature profile at the jet outlet. The experiments were performed at a <i>Reynolds</i> number of 24000 and a swirl number (ratio between the angular velocity of the pipe wall and the bulk velocity in the pipe) of 0.5.</p><p>By means of a specially designed combined X-wire and cold-wire probe it was possible to simultaneously acquire the instantaneous axial and azimuthal velocity components as well as the temperature and compensate the former against temperature variations. The comparison of the swirling and non-swirling cases clearly indicates a modification of the turbulence structure to that effect that the swirling jet spreads and mixes faster than its non-swirling counterpart. It is also shown that the streamwise velocity and temperature fluctuations are highly correlated and that the addition of swirl drastically increases the streamwise<i> passive scalar</i> flux in the near field.</p>

Η παρούσα εργασία πραγματεύεται τη μελέτη και κατασκευή μιας μονάδας ανεμομέτρου θερμού σύρματος (Hot wire anemometer). Η εργασία αυτή εκπονήθηκε στο Εργαστήριο Θερμοκινητήρων του Τμήματος Μηχανολόγων και Αεροναυπηγών Μηχανικών της Πολυτεχνικής Σχολής του Πανεπιστημίου Πατρών. Σκοπός είναι η μελέτη, σχεδιασμός, κατασκευή και δοκιμή μιας μονοκάναλης μονάδας θερμού σύρματος σταθερής θερμοκρασίας (constant temperature anemometer CTA). Η μέθοδος του Hot wire anemometer χρησιμοποιείται για την έμμεση ταχύτητα της ροής, με βάση την συνεχή παρακολούθηση των θερμικών απωλειών γύρω από ένα θερμαινόμενο αισθητήρα. Το αποτέλεσμα δεν είναι μόνο συναρτήσει της ταχύτητας της ροής, αλλά επίσης και ορισμένων άλλων χαρακτηριστικών της ροής. Αρχικά μελετούνται και καταγράφονται οι βασικές αρχές που διέπουν την ανεμομετρία θερμού σύρματος. Στη συνέχεια αναπτύσσεται ο ηλεκτρονικός σχεδιασμός του ηλεκτρονικού κυκλώματος CTA. Ενώ αργότερα γίνεται η υλοποίηση του κυκλώματος στο λογισμικό Altium Designer μέσω της οποίας προκύπτει ο σχεδιασμός των πλακετών PCB. Επιπλέον περιγράφεται αναλυτικά η κατασκευή της διάταξης, περιγράφονται τα κυριότερα υποσυστήματα της και εξηγείτε αναλυτικά η αρχή λειτουργίας της. Τέλος γίνεται βαθμονόμηση του κυκλώματος, βαθμονόμηση του αισθητήρα και πιστοποιείται η σωστή λειτουργία της μονάδας λαμβάνοντας μετρήσεις στην έξοδο ενός τρισδιάστατου ακροφυσίου τύπου Boërger. / The present study deals with the design and construction of a "Hot Wire Anemometer" module. The work has been conducted in Thermal Engines Laboratory of the Mechanical Engineering and Aeronautics Department of the University of Patras, under the supervision of Professor Demos P. Georgiou. The purpose of the current study was the design, construction and testing of a single channel, Constant Temperature Hot Wire Anemometer unit (CTA). The Hot-wire anemometry is a method for indirectly measuring fluid flow velocity, based on monitoring the thermal losses in a heated measuring element. The result is a function of not only the flow velocity, but also of certain other flow parameters. Initially, some basic principles regarding the Hot Wire Anemometer are discussed and some aspects concerning the governing equations are also given. Furthermore, the development of the electronic CTA circuit shown, while later, the final circuit is implemented by employing the Altium Designer Software through which the Printed Circuit Boards (PCB) for the construction are finally obtained. After the detailed presentation of the device construction, the main components and subsystems are discussed in depth. In addition, the principle of operation is also explained in detail. Finally, a fine calibration is made for both, the electronic circuit and the sensor probe. The proper operation of the system as a final product is then certified by obtaining aerodynamic measurements at the exit of a three dimensional Boërger type nozzle.

Η παρούσα διδακτορική διατριβή με τίτλο «Αλληλεπίδραση Ομόρροπα Περιστρεφόμενων Στροβίλων Απορρέματος» αφορά την πειραματική μελέτη του ροϊκού πεδίου της αλληλεπίδρασης δύο ομόρροπα περιστρεφόμενων στροβίλων που δημιουργούνται από επιφάνειες άντωσης. Η μελέτη αυτού του φαινομένου έχει καταστεί ιδιαίτερα σημαντική κυρίως τις τελευταίες δεκαετίες, με αφορμή ατυχήματα αεροσκαφών τα οποία αποδόθηκαν στη δράση του στροβίλου απορρέματος. Η διερεύνηση του μηχανισμού αλληλεπίδρασης και συγχώνευσης του συστήματος δύο στροβίλων έχει αποτελέσει αντικείμενο ενδιαφέροντος για πολλούς ερευνητές σε όλο τον κόσμο. Παρόλα αυτά, ακόμη και σήμερα η γνώση και κατανόηση τέτοιων προβλημάτων δεν ανταποκρίνεται στις σύγχρονες απαιτήσεις. Η ερευνητική δουλεία που έχει γίνει έχει σαν στόχο να συμβάλει στην εξέλιξη της επιστημονικής γνώσης γύρω από το πολύ σημαντικό πρόβλημα του στροβίλου απορρέματος. Η ερευνητική εργασία είναι πειραματική και περιλαμβάνει μετρήσεις του ροϊκού πεδίου πίσω από διαφορική πτέρυγα, τύπου NACA 0030, τοποθετημένη σε ροή αεροσήραγγας ανοικτού κυκλώματος. Σκοπός της μελέτης αυτής είναι η διερεύνηση της δομής και δυναμικής εξέλιξης του τρισδιάστατου πεδίου ταχύτητας-στροβιλότητας του παραγόμενου ζεύγους ομόρροπα περιστρεφόμενων στροβίλων κατά τη διάρκεια της αλληλεπίδρασης τους και της φυσικής διαδικασίας συγχώνευσης που ακολουθεί ως τον τελικό σχηματισμό ενός γραμμικού στροβίλου. Η τεχνική μέτρησης που χρησιμοποιήθηκε είναι η "Ανεμομετρία Θερμού Σύρματος" υπό σταθερή θερμοκρασία (constant temperature hot wire anemometry) με χρήση αισθητήρων δύο (X-probe), τεσσάρων και δώδεκα συρμάτων (multi sensors). Η παρούσα πειραματική μελέτη, στην οποία για πρώτη φορά μετρούνται ταυτόχρονα τα μέσα και στατιστικά χαρακτηριστικά των τρισδιάστατων πεδίων ταχύτητας-στροβιλότητας σε ροή αυτού του τύπου, επιχειρεί να καλύψει ορισμένα από τα επιστημονικά κενά που υπάρχουν. Το ροϊκό πεδίο αξίζει την ιδιαίτερη προσοχή, δεδομένου ότι σημαντικοί ανταγωνιστικοί μηχανισμοί εμφανίζονται να επιβάλλουν το δομικό σχηματισμό του πεδίου του ζεύγους στροβίλων και της δυναμικής διαμήκους εξέλιξής του, συμπεριλαμβανομένης και της "διάρκειας ζωής" τους. Το συγκεκριμένο σχήμα έχει σημαντικό ενδιαφέρον επίσης από άποψη εφαρμογών, με δεδομένη την επιδίωξη της μείωσης της επικινδυνότητας του στροβίλου απορρέματος, καθώς οι ομόρροπα περιστρεφόμενοι στρόβιλοι σχηματίζονται, μερικές φορές πολύ κοντά και σε άλλες θέσεις, εκτός από το άκρο πτέρυγας, όπως για παράδειγμα από τα flaps και την άτρακτο και γενικά από όλες τις επιφάνειες άντωσης του αεροσκάφους. / Experimental evidence is reported regarding the structure of the three-dimensional mean and fluctuating velocity and vorticity fields of a turbulent corotating vortex pair. The presented results constitute part of ongoing research on vortex wakes aiming at contributing to the understanding of trailing vortex interaction dynamics and turbulence structure. The flow field under study is the result of interaction of the pair of co-rotating tip vortices formed by a split wing configuration, consisting of two half wings of equal length l = 24.5cm arranged at equal and opposite angles of attack,  =  8 degrees. The airfoil profile of the wings is that of a NACA0030 with cord length c = 10cm. The wing arrangement is placed at the entrance of the test section of a low turbulence subsonic wind tunnel, of dimensions 30cm  50cm  300cm. In the near wake region, simultaneous measurements of the three-dimensional vector fields of velocity and vorticity in the corotating vortex pair were conducted using an in-house designed and constructed 12-hotwire sensors vorticity probe. The probe consists of three closely separated orthogonal 4–wire velocity sensor arrays, measuring simultaneously the three–dimensional velocity vector at three closely spaced locations on a cross plane of the flow field. This configuration makes possible the estimation of spatial velocity derivatives by means of a forward difference scheme of first order accuracy. The probe was calibrated in-situ in the core region of a round jet rotatable about the pitch and yaw directions. Based on preliminary visualization experiments the cross plane at x/c=0.3 (near wake) has been selected as representative of the vortex pair formation. The evolution of the vortex pair interaction (far wake region) was recorded by a 4-hotwire sensor, capable of measuring simultaneously the three-dimensional velocity vector of the flow filed. After shedding the two vortices are swept along the streamwise direction. The cores initially move away from each other. The rotational velocity field around each core induces a rotational velocity to the other vortex and thus both vortex cores are spiraling around each other, developing a braid of two vortices and deforming the external flow field in the downstream direction. Gradually the interaction flow field links both vortices together until the final merging and the formation of a new stable linear vortex. In the near wake location, the flow field is dictated by the pressure distribution established by the flow around the wings, mobilizing large masses of air and leading to the roll up of fluid sheets. Fluid streams penetrating between the wings collide, creating on the cross plane flow a stagnation point and an ΄΄impermeable΄΄ line joining the two vortex centres. Along this line fluid is directed towards the two vortices, expanding their cores and increasing their separation distance. This feeding process generates a dipole of opposite sign streamwise mean vorticity within each vortex. The rotational flow within the vortices obligates an adverse streamwise pressure gradient leading to a significant streamwise velocity deficit characterizing the vortices. As vortices start to interact, the two cores lose their symmetry and obtain an elliptical formation. The corotating vortex pair is observed to merge at about 0.6 orbit periods and at a downstream distance of 7c from wing tips. Visualization experiments show that the instantaneous flow field of the vortices preserves at all times the structural characteristics of the mean flow field. The vortices are continuously formed close to the wing tips and the fluctuating flow field is the result of changes in the intensity of the formation (e.g. larger or smaller vortex core size) or changes in the position of the cores (wandering) which both should be attributed to secondary attenuating flow instabilities. In this sense the relation of the turbulent field to the mean field is significantly different from cases with no identifiable coherent flow structures (e.g. grid turbulence) or flow fields in which the successive presence of distinct structures result in an idealized but never present mean flow structure.

A key remaining challenge in the design of hypersonic vehicles is the incomplete understanding of the process of boundary-layer transition. Turbulent heating rates are substantially higher than those for a laminar boundary layer, and large uncertainties in transition prediction therefore demand conservative, inefficient designs for thermal protection systems. It is only through close collaboration between theory, experiment, and computation that the state of the art can be advanced, but experiments relevant to flight require ground-test facilities with very low disturbance levels. To enable this work, a unique Mach 6 low-disturbance wind tunnel, previously of NASA Langley Research Center, is established within a new pressure-vacuum blow-down infrastructure at Texas A&M. A 40-second run time at constant conditions enables detailed measurements for comparison with computation. The freestream environment is extensively characterized, with a large region of low-disturbance flow found to be reliably present for unit Reynolds numbers Re < 11×10^6 m-1. Experiments are performed on a 5º half-angle flared cone model at Re = 10×10^6 m-1 and zero angle of attack. For the study of the second-mode instability, well-resolved boundary-layer profiles of mean and fluctuating mass flux are acquired at several axial locations using hot-wire probes with a bandwidth of 330 kHz. The second mode instability is observed to undergo significant growth between 250 and 310 kHz. Mode shapes of the disturbance agree well with those predicted from linear parabolized stability equation (LPSE) computations. A 17% (40 kHz) disagreement is observed in the frequency for most-amplified growth between experiment and LPSE. Possible sources of the disagreement are discussed, and the effect of small misalignments of the model is quantified experimentally. A focused schlieren deflectometer with high bandwidth (1 MHz) and high signal-to-noise ratio is employed to complement the hot-wire work. The second-mode fundamental at 250 kHz is observed, as well as additional harmonic content not discernible in the hot-wire measurements at two and three times the fundamental. A bispectral analysis shows that after sufficient amplification of the second mode, several nonlinear mechanisms become significant, including ones involving the third harmonic, which have not hitherto been reported in the literature.

An experimental investigation into fully developed high aspect ratio channels was undertaken. A review of the literature reveals that there is a need for accurate measurement of the inner peak value of streamwise turbulence intensity despite the large number of studies already completed. The scattered data on this subject could be attributed either to insufficient channel size (aspect ratio or length) or to hot-wire spatial filtering. A new, high quality, channel flow facility was designed and constructed, considering the most recent geometric limitation provided in the literature. To obtain accurate results, data were acquired using hot-wire probes with constant viscous-scale sensing length and were corrected using the most recent correction formula proposed by Smits et al. (2011). The results show dependence of inner peak value on Reynolds number in channels flow - its magnitude increasing with increasing Reynolds number.

The rotating-disk boundary layer is not only a simpler model for the study of cross-flow instability than swept-wing boundary layers but also a useful simplification of many industrial-flow applications where rotating configurations are present. For the rotating disk, it has been suggested that a local absolute instability, leading to a global instability, is responsible for the small variation in the observed laminar-turbulent transition Reynolds number however the exact nature of the transition is still not fully understood. This thesis aims to clarify certain aspects of the transition process. Furthermore, the thesis considers the turbulent rotating-disk boundary layer, as an example of a class of three-dimensional turbulent boundary-layer flows. The rotating-disk boundary layer has been investigated in an experimental apparatus designed for low vibration levels and with a polished glass disk that gave a smooth surface. The apparatus provided a low-disturbance environment and velocity measurements of the azimuthal component were made with a single hot-wire probe. A new way to present data in the form of a probability density function (PDF) map of the azimuthal fluctuation velocity, which gives clear insights into the laminar-turbulent transition region, has been proposed. Measurements performed with various disk-edge conditions and edge Reynolds numbers showed that neither of these conditions a↵ect the transition process significantly, and the Reynolds number for the onset of transition was observed to be highly reproducible. Laminar-turbulent transition for a ‘clean’ disk was compared with that for a disk with roughness elements located upstream of the critical Reynolds number for absolute instability. This showed that, even with minute surface roughness elements, strong convectively unstable stationary disturbances were excited. In this case, breakdown of the flow occurred before reaching the absolutely unstable region, i.e. through a convectively unstable route. For the rough disk, the breakdown location was shown to depend on the amplitude of individual stationary vortices. In contrast, for the smooth (clean-disk) condition, the amplitude of the stationary vortices did not fix the breakdown location, which instead was fixed by a well-defined Reynolds number. Furthermore, for the clean-disk case, travelling disturbances have been observed at the onset of nonlinearity, and the associated disturbance profile is in good agreement with the eigenfunction of the critical absolute instability. Finally, the turbulent boundary layer on the rotating disk has been investigated. The azimuthal friction velocity was directly measured from the azimuthal velocity profile in the viscous sublayer and the velocity statistics, normalized by the inner scale, are presented. The characteristics of this three-dimensional turbulent boundary-layer flow have been compared with those for the two-dimensional flow over a flat plate and close to the wall they are found to be quite similar but with rather large differences in the outer region. / <p>QC 20150119</p>

Experimental aeroacoustic research was conducted on a wind turbine specific airfoil at low Reynolds numbers. The goal of this thesis was to study trailing edge noise generation from the airfoil and investigate correlations between the noise and the flow field. Before experiments were performed the current wind tunnel had to be modified in order to make it more suitable for aeroacoustic tests. Sound absorbing foam was added to the inside of the tunnel to lower the background noise levels and turbulence reduction screens were added which lowered the turbulence. An S822 airfoil was chosen because it is designed for low Reynolds flows attainable in the wind tunnel which are on the order of 104. Smoke wire flow visualization was used to gain insight into the airfoil wake development and oil film flow visualization was used to qualitatively assess the boundary layer development. Laser Doppler anemometry (LDA) was used to measure two components of velocity at high data rates in the airfoil wake. Wake profiles were measured in addition to single point measurements to determine the velocity spectrum. A microphone was mounted inside the test section in order to measure the trailing edge noise. Initial plans included measuring the trailing edge noise with a microphone array capable of quantifying and locating noise sources. Although an array was built and beamforming code was written it was only used in preliminary monopole source tests. Oil film results showed the behaviour of the boundary layer to be consistent with previous low Reynolds number experiments. LDA results revealed sharp peaks in the velocity spectra at 1100 Hz from U0 = 15–24 m/s, and 3100 and 3800 Hz, from U0 = 25–35 m/s, which were inconsistent with vortex shedding results of previous researchers. Also present were a series of broad peaks in the spectra that increase from 1200–1700 Hz in the U0 = 25–35 m/s range. The shedding frequency from the smoke wire flow visualization was calculated to be 1250 Hz at U0 = 26 m/s. These sharp peaks were also present in the acoustic spectrum. It was reasoned that these peaks are due to wind tunnel resonance which is a common occurrence in hard wall wind tunnels. In particular the tone at 1100 Hz is due to a standing wave with a wavelength equal to half the tunnel width. The shedding frequency from the smoke wire flow visualization was calculated to be 1100 Hz at U0 = 20 m/s. These tones exhibited a “ladder-like” relationship with freestream velocity, another aspect indicative of wind tunnel resonance. It was reasoned that the wind tunnel resonance was forcing the shedding frequency of the airfoil in the U0 = 15–24 m/s range, and in the U0 = 25–35 m/s range, the shedding frequency corresponded to the broad peaks in the LDA spectra.

Este trabalho apresenta um estudo experimental do efeito da razão de bloqueio em um canal aerodinâmico no Número de Strouhal e o fenômeno da biestabilidade. É estudado o escoamento turbulento sobre um cilindro e também sobre dois cilindros dispostos lado a lado, onde fez-se uso de cilindros de vários diâmetros a fim de variar a razão de bloqueio no canal. Dois tipos de espaçamento entre os tubos são estudados. A técnica experimental consiste na medição de flutuações de velocidades em um canal aerodinâmico utilizando a técnica de anemometria de fio quente. Os dados obtidos da medição no canal aerodinâmico são tratados com o uso de ferramentas estatísticas, espectrais e de ondaletas. Para um cilindro, os resultados confirmam o aumento do número de Strouhal com o aumento da razão de bloqueio, na faixa do número de Reynolds utilizada. Razões de bloqueio mais baixas podem acarretar diminuição do número de Strouhal, também em função do número de Reynolds. Os resultados confirmam a existência do fenômeno da biestabilidade no escoamento sobre dois cilindros dispostos lado a lado, assim como a influência da razão de bloqueio sobre o fenômeno, sendo mais predominante em um dos espaçamentos estudados. Para razões de bloqueio altas, o fenômeno da biestabilidade pode não ocorrer ou pouco ocorre. Para razões de bloqueio mais baixas podemos ter também a não ocorrência do fenômeno em função das dimensões dos tubos serem mais reduzidas, fazendo com que a captação do fenômeno também seja reduzida. / This paper presents an experimental study of the effect of blockage ratio in a aerodynamic channel on Strouhal number and the bistability phenomenon. It studied the turbulent flow around a single cylinder and also on two cylinders arranged side-by-side, where use has been made of cylinders of various diameters to vary the blockage ratio of the channel. Two types of pitch to diameter ratio are studied. The experimental technique consists of measuring velocity fluctuations in aerodynamic channel using the technique of hot-wire anemometry. The data obtained from measuring the aerodynamic channel are treated with the use of statistical tools, spectral and wavelet analysis. For a single cylinder, the results confirm the increase of the Strouhal number with increasing blockage ratio in the range of Reynolds number used. Lower blockage ratio can cause a decrease of the Strouhal number, also a function of Reynolds number. The results confirm the existence of the bistability phenomenon in the flow on two cylinders arranged side-by-side, as well as the influence of blockage ratio on the phenomenon, being more predominant in one of the row spacings. For higher blockage ratios, the bistability phenomenon may not occur or occurs shortly. For lower blockage ratio, due to the smaller dimensions of the tubes the phenomenon may not occur on the capture of the phenomenon is also reduced with the present experimental technique.

Este trabalho apresenta um estudo acerca dos principais parâmetros que caracterizam o fenômeno da biestabilidade em dois tubos dispostos lado a lado submetidos a escoamento cruzado turbulento. A técnica experimental da anemometria de fio quente em canal aerodinâmico é aplicada na medição das flutuações de velocidade do escoamento após os tubos. As séries temporais obtidas são utilizadas como dados de entrada para determinação das funções densidade de probabilidade (PDF) usando um modelo de mistura finita, de acordo com uma função t de Student assimétrica e com o auxílio do método de Monte Carlo. Transformadas de ondaletas discretas e contínuas são aplicadas na filtragem das séries temporais para determinadas bandas de frequências e na análise do conteúdo de energia destes sinais. Através de conceitos de sistemas caóticos, é realizada a reconstrução do atrator do problema pelo método dos atrasos temporais, a partir das séries experimentais de velocidade, permitindo a determinação da dimensão de imersão e o cálculo do maior expoente de Lyapunov. Os resultados mostram a existência de dois patamares distintos de velocidade média nas séries temporais, correspondentes aos dois modos do escoamento, cada qual com números de Strouhal e funções densidade de probabilidade distintas. Uma análise conjunta das componentes axial e transversal do escoamento e suas PDF indicam as regiões no plano de medições onde o fenômeno se manifesta, sendo que reconstruções da trajetória filtrada das séries temporais para determinadas bandas de frequências apresentam características caóticodeterminísticas. O maior expoente de Lyapunov das séries experimentais é positivo, o que é um indício de comportamento caótico. / This work presents a study of the main parameters that characterize the phenomenon of bistability in two tubes placed side by side submitted to turbulent crossflow. The experimental technique of hot wire anemometry in aerodynamic channel is applied in the measurement of velocity fluctuations of the flow after the tubes. The time series obtained are used as input data for determining the probability density functions (PDF) using a finite mixture model, according to an asymmetric Student t function and with the aid of a Monte Carlo method. Wavelet transforms are applied in discrete and continuous filtering of time series for certain frequency bands and in the analysis of the energy content of these signals. By means of chaotic systems concepts, the attractor reconstruction of the problem is performed using the method of time delays from the experimental series of velocity, allowing the determination of the embedding dimension and calculating the largest Lyapunov exponent. The results show the existence of two different levels of mean velocity in time series, corresponding to two flow modes, each one with different Strouhal numbers and probability density functions. A joint analysis of axial and transverse components of flow and its PDF indicate the regions in the measurement plan where the phenomenon is manifested, and reconstructions of the trajectory of the filtered time series for certain frequency bands have chaotic-deterministic characteristics. The largest Lyapunov exponent of experimental series is positive, which is an indication of chaotic behavior.