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A fundamental study of two turbulent directly opposed impinging jets in a stagnant ambient fluid, unconfined or uninfluenced by walls is presented. By experimental investigation and numerical modeling, the main characteristics of direct impingement of two turbulent axisymmetric round jets under seven different geometrical and flow rate configurations (L*= L/d = { 5, 10, 20 }, where L is nozzle to nozzle separation distance and d is nozzle diameter, and Re = { 1500, 4500, 7500, 11000 }) are discussed. Flow visualization and velocity measurements performed using various laser based techniques have revealed the effects of Reynolds number, Re, and nozzle to nozzle separation, L, on the complex flow structure. Although locally valid, the classical analysis of turbulence is found unable to provide reliable results within the highly unstable and unsteady impingement region. When used to simulate the present flow, the assessment of the performance of three distinct k - epsilon turbulence models showed little disagreement between computed and experimental mean velocities and poor predictions as far as turbulence parameters are concerned.

A fundamental study of two turbulent directly opposed impinging jets in a stagnant ambient fluid, unconfined or uninfluenced by walls is presented. By experimental investigation and numerical modeling, the main characteristics of direct impingement of two turbulent axisymmetric round jets under seven different geometrical and flow rate configurations (L*= L/d = { 5, 10, 20 }, where L is nozzle to nozzle separation distance and d is nozzle diameter, and Re = { 1500, 4500, 7500, 11000 }) are discussed. Flow visualization and velocity measurements performed using various laser based techniques have revealed the effects of Reynolds number, Re, and nozzle to nozzle separation, L, on the complex flow structure. Although locally valid, the classical analysis of turbulence is found unable to provide reliable results within the highly unstable and unsteady impingement region. When used to simulate the present flow, the assessment of the performance of three distinct k - epsilon turbulence models showed little disagreement between computed and experimental mean velocities and poor predictions as far as turbulence parameters are concerned.

An experimental scale model study was conducted to investigate the onset of fluidelastic instability in a tube array subjected to axisymmetric jet flow. A tube array was constructed using aluminum tubes with 44.45 mm outer diameter, $D$, which were arranged in a square pattern with 88 mm pitch, $P$. The pitch to diameter ratio, $P/D$, was approximately 2.0. The tubes were flexibly mounted using threaded rod and tuned to a first mode natural frequency, $f_n$, of 9 Hz. Auxiliary damping devices were added to each tube, and tuned, to achieve a damping ratio, $\zeta$, of 1 % of critical. The mass damping parameter, $m(2 \pi \zeta)/(\rho D^{2})$, of the tube array was 27.9. The tube array was tested under uniform flow conditions in McMaster University's 2 ft wind tunnel to establish the critical reduced velocity, $V_{cr}/(f_n D)$, of 30.0 at the onset of fluidelastic instability. The uniform flow test established a basis for comparing the results with the existing literature and evaluating the validity of the proposed partial admission calculation. The tube array was also tested in open air using an axisymmetric jet, with two different physical arrangements, the first with the jet aimed between tubes and perpendicular to the tube spans and the second with the jet aimed at a tube face and perpendicular to the tube spans. In each case the jet flow velocity was incrementally increased to characterize the onset of fluidelastic instability. To characterize the flow dispersion through the tube array a series of velocity profile measurements were also collected. The measured velocity profiles were used to estimate the spanwise function of transverse average gap velocity, $\bar{V}(x)$, which was used to predict the equivalent critical uniform gap flow velocity, $V_{cr}$, using the concept of partial admission. The predicted $V_{cr}$ values showed reasonable agreement with the experimental results. However, the prediction method did indicate instabilities in tube rows where instability was not actually observed. A simplified prediction approach was developed which was based on using a predicted three dimensional velocity profile, $V(x,y)$, at the $z$ location of the first row tube gap, under the assumption of free field conditions, to calculate an estimate of the spanwise function of transverse average gap velocity, $\bar{V}(x)$. Although the predictions of $V_{cr}$ agreed reasonably well with the experimental results, first row instabilities were not observed in any of axisymmetric jet flow experiments. Therefore, this method can be used to estimate the the critical uniform gap velocity, $V_{cr}$, but not the spatial location of the instability. Based on the results of the experiments and calculations, adoption of the modified partial admission formula is recommended and possible avenues for further investigation and verification are suggested. / Thesis / Master of Applied Science (MASc)

Creating effective models predicting particle entrainment behavior within axisymmetric turbulent jets is of significant interest to many areas of study. Research into multiphase flows within turbulent structures has primarily focused on specific geometries for a target application, with little interest in generalized cases. In this research, the entrainment characteristics of various particle sizes and densities were simulated by determining the distribution of particles across a surface after the particles had fallen out of entrainment within the jet core. The model was based on an experimental set-up created by Lieutenant Zachary Robertson, which consists of a particle injection system designed to load particles into a fully developed pipe [1]. This pipe flow then exits into an otherwise quiescent environment (created within a wind tunnel), creating an axisymmetric turbulent round jet. The particles injected were designed to test the effect of both particle size and density on the entrainment characteristics. The data generated by the model indicated that, for all particle types tested, the distribution across the bottom surface of the wind tunnel followed a standard Gaussian distribution. Experimentation yielded similar results, with the exception that some of the experimental trials showed distributions with significantly non-zero skewness. The model produced results with the highest correlation to experimentation for cases with the smallest Stokes number (small size/density), indicating that the trajectory of particles with the highest level of interaction with the flow were the easiest to predict. This was contrasted by the high Stokes number particles which appear to follow standard rectilinear motion. / Master of Science

Στην παρούσα εργασία παρουσιάζονται πειραματικά αποτελέσματα των τρισδιάστατων διανυσμάτων των τυρβωδών πεδίων ταχύτητας και στροβιλότητας στην εγγύς περιοχή της τυρβώδους ορθογωνικής δέσμης με λόγο σύγκλισης 6. Οι τυρβώδεις ορθογωνικές ελεύθερες δέσμες έχουν πρακτικό ενδιαφέρον για την καύση, την πρόωση και τις περιβαλλοντικές ροές. Για την μέτρηση των μέσων και στατιστικών χαρακτηριστικών των συνιστωσών των δυο πεδίων σε διαφορετικές θέσεις στην εγγύς περιοχή της δέσμης χρησιμοποιήθηκε κεφαλή 12-αισθητήρων θερμού νήματος αποτελούμενη από τρεις κεφαλές 4 αισθητήρων. Η κεφαλή 12-αισθητήρων μετράει ταυτόχρονα τις τρεις συνιστώσες της ταχύτητας σε τρεις διαφορετικές θέσεις και επιτρέπει τον υπολογισμό των χωρικών παραγώγων του ανύσματος της ταχύτητας με την μέθοδο των πεπερασμένων διαφορών με ακρίβεια πρώτης τάξεως. Η κατασκευή της κεφαλής 12-αισθητήρων και η τεχνική μέτρηση βασίζεται στην εργασία των Lemonis & Drakos (1995) και Lemonis (1995) και έχει περαιτέρω βελτιωθεί στο Εργαστήριο Τεχνικής Θερμοδυναμικής του Πανεπιστημίου Πατρών. Οι μετρήσεις διεξήχθησαν σε αριθμό Reynolds, ReD = 21000 σε αποστάσεις κατά μήκος της ροής ίσες προς x/D =1, 3, 6 και 11, όπου D είναι το πλάτος του ακροφυσίου. Η αξιοπιστία της κεφαλής 12-αισθητήρων εκτιμήθηκε σε σύγκριση με τα αποτελέσματα της κεφαλής αισθητήρων X. Τα αποτελέσματα από τις μετρήσεις του πεδίου ταχύτητας και με τις δύο κεφαλές είναι σε καλή συμφωνία, εκτός από τις θέσεις όπου οι μεγάλες χωρικές κλίσεις της ταχύτητας και η τρισδιαστατότητα του πεδίου ταχύτητας υπονομεύουν τις μετρήσεις με την κεφαλή αισθητήρων Χ. Οι στατιστικές ιδιότητες των πεδίων της ταχύτητας και στροβιλότητας που υπολογίστηκαν από τις μετρήσεις με την κεφαλή 12-αισθητήρων εκτιμιούνται σε σύγκριση με πειραματικά και υπολογιστικά αποτελέσματα άλλων ερευνητών. Οι κατανομές των κυμαινόμενων πεδίων της ταχύτητας και στροβιλότητας δείχνουν ότι στην περιοχή του πυρήνα δυναμικού οι τιμές είναι αρκετά χαμηλές στον κεντρικό άξονα της δέσμης και αρκετά υψηλές στα διατμητικά στρώματα. Κατάντι της ροής οι διακυμάνσεις της ταχύτητας και στροβιλότητας μεταφέρονται από τα διατμητικά στρώματα προς το κέντρο και τις άκρες της δέσμης και οδηγούν στη συγχώνευση των διατμητικών στρωμάτων. Τα αποτελέσματα επιβεβαιώνουν επίσης τα υψηλά επίπεδα του ρυθμού εκφυλισμού (dissipation rate) στα διατμητικά στρώματα. Το ισοζύγιο της τυρβώδους ενέργειας παρουσιάζει σημαντικές διαφορές με το αντίστοιχο της επίπεδης δέσμης. Η σύγκριση των όρων της εξίσωσης της μέσης τετραγωνικής διακύμανσης της στροβιλότητας στη θέση x/D=11 δείχνει ότι η περιστροφή και η διάταση λόγω των διακυμάνσεων του ρυθμού παραμόρφωσης (strain rate) εξισορροπείται από τον ιξώδη εκφυλισμό της στροβιλότητας. Οι ανισοτροπίες στην εγγύς περιοχή της τυρβώδους ορθογωνικής δέσμης ερευνώνται και συζητούνται λεπτομερώς. Για την ερευνά της δομικής εξέλιξης της τυρβώδης ορθγωνικής δέσμης στην εγγύς περιοχή χρησιμοποιήθηκε επίσης και η μέθοδος PIV. Οι μετρήσεις με την μέθοδο PIV προσφέρουν το πλεονέκτημα της απεικόνισης της ροής μαζί με τη δυνατότητα καλύτερης κατανόησης των φαινόμενων της ροής, και ειδικότερα, πώς η δημιουργία, η αλληλεπίδραση και η συγχώνευση των στροβίλων συμβάλλουν στην ανάπτυξη της ορθογωνικής δέσμης. Τα αποτελέσματα των κατανομών φασμάτων ισχύος δείχνουν ότι μετά το τέλος του πυρήνα δυναμικού η ενισχυμένη συχνότητα αντιστοιχεί σε αριθμό Strouhal St=f•yc/U0≈0,11. Οι κατανομές της πυκνότητας ελικότητας στις περιοχές των διατμητικών στρωμάτων για x/D=3, 6, 11 δείχνουν μια τάση των ολικών διανυσμάτων της ταχύτητας και στροβιλότητας να ευθυγραμμιστούν. Από την άλλη, στις περιοχές των διατμητικών στρωμάτων για x/D=1 όπου το ολικό διάνυσμα της ταχύτητας είναι περίπου κάθετο προς την μέση ροή οι κατανομές παρουσιάζουν αντίθετη μορφή, όπως θα αναμενόταν. Η συλλογή πληροφοριών στην παρούσα έρευνα και η σύγκριση με τα ήδη υπάρχοντα στην βιβλιογραφία πειραματικά αποτελέσματα για τις τυρβώδες δέσμες αναμένεται να διευρύνουν περαιτέρω τη γνώση σχετικά με τη δομή των ελεύθερων διατμητικών ροών. / In the present work the three-dimensional velocity and vorticity vector fields in the near field of the rectangular turbulent jet with aspect ratio 6 have been experimentally investigated. Turbulent rectangular jets are prototypical free shear flows of practical interest in propulsion, combustion and environmental flows. The presented data, consisting of distributions of mean and statistical characteristics of the components of the two fields at several locations within the jet’s near field region, were obtained by using an in-house constructed 12-sensor hot wire probe consisting of three closely separated orthogonal 4-hot wire velocity arrays. The probe measures the three components of velocity simultaneously at three closely spaced locations. Spatial velocity derivatives are estimated using a forward difference scheme of first order accuracy. Streamwise velocity derivatives are estimated using Taylor’s frozen turbulence hypothesis. The 12-sensor construction and measurement technique relies upon previous work of Lemonis & Dracos (1995) and Lemonis (1995) and has been further improved and refined at the Laboratory of Applied Thermodynamics of the University of Patras. Measurements have been conducted in a jet with Reynolds number ReD = 21000 at nozzle distances, x/D =1, 3, 6 and 11, where D is the width of the nozzle. The performance of the 12-sensor probe is investigated in comparison with X-sensor probe measurements. Results referring to measurements of velocity with both sensors are in good agreement, except in locations where the steep velocity gradients and the three dimensionality of the velocity field undermine X-wire probe measurements. The statistical properties of the velocity-vorticity fields based on measurements with the 12-sensor probe are presented in comparison with several experimental and direct numerical simulation data of other researchers. Distributions of fluctuating velocity –vorticity fields show that in the potential core region the values are low on the centerline of the jet and quite high in the shear layers. Downstream the velocity-vorticity fluctuations spread from the shear layer towards the centre and the edge of the jet leading to merging of the two mixing layers. The results also confirm the high levels of dissipation rate in the shear layers. The turbulent energy balance shows important differences to that in plane jets. The budget of the transport equation for fluctuating enstrophy at x/D=11 indicates that the rotation and stretching by the fluctuating strain rate is balanced by the viscous dissipation of vorticity. The anisotropies in the near field of the turbulent rectangular jet are illustrated and discussed in detail. The structure development of a rectangular turbulent jet in the near field region has been also investigated experimentally using PIV. The results obtained with PIV measurements offer the advantages of flow visualization along with the possibility of better understanding the flow phenomena, in particular, how the formation, interaction and merging of vortices contribute to the development of the rectangular jet. The results of spectra distributions indicate that the most amplified frequency after the end of the potential core give rise to a Strouhal Number St=f•yc/U0≈0,11. In the regions of turbulent shear layers at x/D=3, 6, 11 the pdf’s of the relative helicity density h have shapes showing a preferred tendency for the total velocity and vorticity vectors to be aligned. On the other hand, in the regions of turbulent shear layers at x/D=1 where the total vorticity vector is more nearly orthogonal to the mean flow, the pdf’s show the opposite shape, as would be expected. Comparison and integration of the obtained information with the existing body of experimental evidence on turbulent rectangular jets is expected to enhance knowledge on the turbulence structure in free shear flows.

In single phase, steady, turbulent axisymmetric jets, the time-averaged velocity field can be characterised by the decay in centreline velocity and increased spread with increasing distance from the jet orifice. In a two-phase or ‘particle-laden’ jet, the particles will modulate the jet turbulence and exchange momentum with the gas phase. Consequently, these effects reduce both the centreline velocity decay and spreading rates with respect to the single-phase jet. Empirical exponential scaling factors were found by previous authors to describe the reduced centreline decay and spreading rates well for low Stokes numbers. In this thesis, power-law scaling factors are found to scale well a wide range of centreline velocity decay and spreading rate data published over the past 40 years, for a wide range of Stokes numbers. The power-law scaling is composed of three different regimes. For low Stokes numbers St₀ ≲20, it is found that the gas phase centreline velocity, u₀/uc collapses if plotted as a function of x/D(1 + Ø₀)⁻¹, and the velocity profile half widths r₁/ ₂ collapse if plotted as a function of x/D(1+Ø₀)⁻¹. Here, u₀ is the exit velocity, Ø₀ is the exit mass loading, x is the axial coordinate and D is the pipe diameter. For intermediate Stokes numbers, u₀/uc collapses if plotted as a function of x/D(1 + Ø₀)⁻¹ and r₁/ ₂ collapses if plotted as a function of x/D(1 + Ø₀)⁻¹/². For high Stokes numbers St₀ ≳ 200, u₀/uc collapses if plotted as a function of x/D(1 + Ø₀)⁻¹/² and the half width is approximately independent of Ø₀. In addition to the velocity of the gas phase, other aspects of particle- laden jets are found to be amenable to scaling by power-law functions. It is found that reported solid phase mass flux data scales similarly to gas phase measurements. Limited solid phase concentration and entrainment measurements reported in the literature are also found to scale by power-law functions. Whereas that limited data was obtained from the literature, measurements of the distribution of particles in particle-laden jets were conducted to further assess the validity of the scaling regimes to the solid phase. A planar light scattering technique is conducted to measure the distribution of particles in an axisymmetric jet and their subsequent scaling (or lack thereof) are reported for a variation in Ø₀, Stokes number and gas phase jet exit density. For Stokes numbers based on the pipe friction velocity St* ₀ ∼ 1, half widths of particle distributions were found to scale with x/D(1+Ø₀)⁻¹/² . The apparent centreline concentration was found to be independent of Ø₀ at this same St* ₀ . For Stokes numbers based on the pipe friction velocity St*₀ < 1, half widths are independent of Ø₀. The effect of the other parameters, i.e. Stokes number and density ratio, on centreline distributions and half widths are also investigated. Measurements of particle distributions, delivered via an annular channel, in a triangular oscillating jet (OJ) flow are also reported for a variation in momentum ratio, the ratio of OJ momentum to channel momentum and mass loading. The results of the variation in momentum ratio on particle distributions are compared with an existing precessing jet (PJ) study. It is the aim of this study to determine the experimental conditions for which the OJ nozzle is superior to the PJ nozzle. The use of an OJ nozzle is preferable at an industrial scale by virtue of its lower driving pressure compared with a PJ nozzle. It is found that particle distributions in a PJ flow spread at a greater rate with increasing momentum ratio compared with the spread of particles in an OJ flow. However, at momentum ratios approximately less than unity, the absolute spread from an OJ is greater. This also corresponds to nozzle driving pressure less than approximately 10kPA. For an increase in mass loading, the spread of particle distribution in the OJ decreases and recirculation increases. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1337352 / Thesis (M.Eng.Sc.) -- University of Adelaide, School of Mechanical Engineering, 2008

In single phase, steady, turbulent axisymmetric jets, the time-averaged velocity field can be characterised by the decay in centreline velocity and increased spread with increasing distance from the jet orifice. In a two-phase or ‘particle-laden’ jet, the particles will modulate the jet turbulence and exchange momentum with the gas phase. Consequently, these effects reduce both the centreline velocity decay and spreading rates with respect to the single-phase jet. Empirical exponential scaling factors were found by previous authors to describe the reduced centreline decay and spreading rates well for low Stokes numbers. In this thesis, power-law scaling factors are found to scale well a wide range of centreline velocity decay and spreading rate data published over the past 40 years, for a wide range of Stokes numbers. The power-law scaling is composed of three different regimes. For low Stokes numbers St₀ ≲20, it is found that the gas phase centreline velocity, u₀/uc collapses if plotted as a function of x/D(1 + Ø₀)⁻¹, and the velocity profile half widths r₁/ ₂ collapse if plotted as a function of x/D(1+Ø₀)⁻¹. Here, u₀ is the exit velocity, Ø₀ is the exit mass loading, x is the axial coordinate and D is the pipe diameter. For intermediate Stokes numbers, u₀/uc collapses if plotted as a function of x/D(1 + Ø₀)⁻¹ and r₁/ ₂ collapses if plotted as a function of x/D(1 + Ø₀)⁻¹/². For high Stokes numbers St₀ ≳ 200, u₀/uc collapses if plotted as a function of x/D(1 + Ø₀)⁻¹/² and the half width is approximately independent of Ø₀. In addition to the velocity of the gas phase, other aspects of particle- laden jets are found to be amenable to scaling by power-law functions. It is found that reported solid phase mass flux data scales similarly to gas phase measurements. Limited solid phase concentration and entrainment measurements reported in the literature are also found to scale by power-law functions. Whereas that limited data was obtained from the literature, measurements of the distribution of particles in particle-laden jets were conducted to further assess the validity of the scaling regimes to the solid phase. A planar light scattering technique is conducted to measure the distribution of particles in an axisymmetric jet and their subsequent scaling (or lack thereof) are reported for a variation in Ø₀, Stokes number and gas phase jet exit density. For Stokes numbers based on the pipe friction velocity St* ₀ ∼ 1, half widths of particle distributions were found to scale with x/D(1+Ø₀)⁻¹/² . The apparent centreline concentration was found to be independent of Ø₀ at this same St* ₀ . For Stokes numbers based on the pipe friction velocity St*₀ < 1, half widths are independent of Ø₀. The effect of the other parameters, i.e. Stokes number and density ratio, on centreline distributions and half widths are also investigated. Measurements of particle distributions, delivered via an annular channel, in a triangular oscillating jet (OJ) flow are also reported for a variation in momentum ratio, the ratio of OJ momentum to channel momentum and mass loading. The results of the variation in momentum ratio on particle distributions are compared with an existing precessing jet (PJ) study. It is the aim of this study to determine the experimental conditions for which the OJ nozzle is superior to the PJ nozzle. The use of an OJ nozzle is preferable at an industrial scale by virtue of its lower driving pressure compared with a PJ nozzle. It is found that particle distributions in a PJ flow spread at a greater rate with increasing momentum ratio compared with the spread of particles in an OJ flow. However, at momentum ratios approximately less than unity, the absolute spread from an OJ is greater. This also corresponds to nozzle driving pressure less than approximately 10kPA. For an increase in mass loading, the spread of particle distribution in the OJ decreases and recirculation increases. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1337352 / Thesis (M.Eng.Sc.) -- University of Adelaide, School of Mechanical Engineering, 2008

Flow control of transitional shear flows is investigated by means of numerical simulations. The attenuation of three-dimensional wavepackets of Tollmien-Schlichting (TS) and streaks in the boundary layer is obtained using active control in combination with localised sensors and actuators distributed near the rigid wall. Due to the dimensions of the discretized Navier-Stokes operator, reduced-order models are identified, preserving the dynamics between the inputs and the outputs of the system. Balanced realizations of the system are computed using balanced truncation and system identification. We demonstrate that the energy growth of the perturbations is substantially and efficiently mitigated, using relatively few sensors and actuators. The robustness of the controller is analysed by varying the number of actuators and sensors, the Reynolds number, the pressure gradient and by investigating the nonlinear, transitional case. We show that delay of the transition from laminar to turbulent flow can be achieved despite the fully linear approach. This configuration can be reproduced in experiments, due to the localisation of sensing and actuation devices. The closed-loop system has been investigated for the corresponding twodimensional case by using full-dimensional optimal controllers computed by solving an iterative optimisation based on the Lagrangian approach. This strategy allows to compare the results achieved using open-loop model reduction with model-free controllers. Finally, a parametric analysis of the actuators/ sensors placement is carried-out to deepen the understanding of the inherent dynamics of the closed-loop. The distinction among two different classes of controllers – feedforward and feedback controllers - is highlighted. A second shear flow, a confined turbulent jet, is investigated using particle image velocimetry (PIV) measurements. Proper orthogonal decomposition (POD) modes and Koopman modes via dynamic mode decomposition (DMD) are computed and analysed for understanding the main features of the flow. The frequencies related to the dominating mechanisms are identified; the most energetic structures show temporal periodicity. / <p>QC 20130207</p>

Relatively few studies have been carried out on the turbulent wake structure of a finite circular cylinder and a stack partially immersed in a flat-plate turbulent boundary layer. There is a need to develop a better understanding of the wakes of these structures, since they have many important engineering applications. This thesis investigates the influence of the aspect ratio on the wake of a finite circular cylinder and the effects of the ratio of jet flow velocity to crossflow velocity (velocity ratio, R) on the wake of a stack in a cross-flow. <p>The wake characteristics of flows over a finite circular cylinder at four different aspect ratios (AR = 3, 5, 7 and 9) were investigated experimentally at a Reynolds number of ReD = 6104 using two-component thermal anemometry. Each cylinder was mounted normal to a ground plane and was either completely or partially immersed in a flat-plate turbulent boundary layer. The ratio of boundary layer thickness to the cylinder diameter was 3. <p>A similar turbulent wake structure (time-averaged velocity, turbulence intensity, and Reynolds shear stress distributions) was found for the cylinders with AR = 5, 7, and 9, while a distinctly different turbulent wake structure was found for the cylinder with AR = 3. This was consistent with the results of a previous study that focused on the time-averaged streamwise vortex structures in the wake. In addition, irrespective of the value of AR, high values were observed for the skewness and flatness factors around the free end of the cylinders, which may be attributed to the interaction of the tip vortex structures and downwash flow that dominates this region of the cylinder.<p>The wake characteristics of a stack of aspect ratio AR = 9 were investigated using both the seven-hole pressure probe and thermal anemometry. The seven-hole probe was used to measure the three components of the time-averaged velocity field, while the thermal anemometry was used to measure two components of the turbulent velocity field at various downstream locations from the stack. The stack was mounted normal to the ground plane and was partially immersed in a flat-plate turbulent boundary layer, for which the ratio of boundary layer thickness to the stack diameter was 4.5. In addition, measurements of the vortex shedding frequency were made with a single-component hot-wire probe. The cross-flow Reynolds number was ReD = 2.3 x 104, the jet Reynolds number ranged from Red = 7.6 x 103 to 4.7 x 104, and R was varied from 0 to 3. <p>In the stack study, three flow regimes were identified depending on the value of R: the downwash (R < 0.7), cross-wind-dominated (0.7 < R < 1.5), and jet-dominated (R ≥ 1.5) flow regimes. Each flow regime had a distinct structure for the time-averaged velocity and streamwise vorticity fields, and turbulence characteristics, as well as the variation of the Strouhal number and the power spectrum of the streamwise velocity fluctuations along the stack height. The turbulence structure is complex and changes in the streamwise and wall-normal directions within the near and intermediate stack and jet wakes. In the downwash and crosswind-dominated flow regimes, two pairs of counter-rotating streamwise vortex structures were identified within the stack wake. The tip-vortex pair and base-vortex pair were similar to those found in the wake of a finite circular cylinder, located close to the free end and the base of the stack (ground plane), respectively. In the jet-dominated flow regime, a third pair of streamwise vortex structures was observed, referred to as the jet-wake vortex pair, which occurred within the jet-wake region above the free end of the stack. The jet-wake vortex pair has the same orientation as the base vortex pair and is associated with the jet rise.