Passive scalar diffusion in the near field region of turbulent rectangular submerged free jets

Jets are a common way to transfer mass among fluids, or from a fluid to a surface. At moderate Reynolds numbers and low turbulent intensities the jet exhibits a Near Field Region (NFR) several diameters long. The paper presents numerical results and a theoretical model for the passive scalar diffusion of a submerged free jet in the NFR. Large Eddy Simulations (LES), in the Reynolds number range of 5000–40,000 and the Schmidt number range 1–100, are performed obtaining the passive scalar fields. Three mathematical models for the passive scalar diffusion are presented; the first one is valid in the NFR, specifically in the Undisturbed Region of Flow (URF), and the other two, obtained under the hypotheses of Tollmien and Görtler momentum spreading, are valid in the Potential Core Region (PCR). The last two models employ a turbulent Schmidt number inversely proportional to the mean velocity gradient, conclusion obtained from the LES numerical results. The self-similar solutions of the passive scalar show good agreement with the LES results. The wide range of Reynolds and Schmidt numbers investigated gives generality to the results

Large eddy simulation and self-similarity analysis of the momentum spreading in the near field region of turbulent submerged round jets

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Self-Similarity in turbulent round jets has been the object of investigation from several decades. The evolution of turbulent submerged jets is characterized by the presence of two regions: the region of flow establishment, or near field region (NFR) and the fully developed region (FDR), or far-field region (FFR). The momentum spreading in the FDR is known to be self-similar and few mathematical models have been presented in the past to describe it. The flow evolution in the NFR has been rarely studied since there is a certain consensus on the idea that the flow in the NFR is not self-similar. In this work, we study the flow evolution of a turbulent submerged round jet by means of large eddy simulation (LES) at several Reynolds numbers ranging from 2492 to 19,988. Three new self-similar laws are proposed to describe the flow evolution in the NFR, one for the initial region, called Undisturbed Region of Flow, (URF), and two for the final region, the potential core region (PCR). The numerical results presented in this work are also validated with the self-similar laws for the FDR proposed by Tollmien (1926) and Görtler (1942), and the experimental data of Hussein et al. (1994), and Panchapakesan and Lumley (1993), in the FDR; those of Davies et al. (1963), in the PCR; and van Hout et al. (2018), in the URF. The conclusion is that previous inability to find the self-similarity law in the NFR is due to the attempt to find a unique self-similar variable to describe the momentum spreading in both the URF and the PCR

På en världs avstånd? : en jämförande undersökning av romersk influens på landsbygdsbosättningar i Storbritannien och Sverige under romersk järnålder

Den här studien gäller Romersk järnålder i Sverige och Storbritannien med fokus på den senare. Det är en komparativ analys av utvalda delar av den materiella kulturenfrån ett antal olika lokaler i Sverige och Storbritannien med intentionen att skapa vidare förståelse rörande romersk influens i dessa regioner. Vidare är intentionen att uppsatsen skall undersöka möjliga likheter eller skillnader och därigenom dra slutsatser om romerska influensen var stark eller svag i de utvalda bosättningarna i Storbritannien och Sverige. Var den så kallade Romaniseringen för samtliga invånare eller var den enbart reserverad för eliten?This is a study of the Roman Iron Age in both Sweden and Britain but with a focus on the latter. The study includes a comparative analysis of selected goods in the material culture at a number of different sites in Sweden and Britain in the aim of understanding the extent of the Roman influence at these sites. The aims of the essay is to investigate if we can notice similarities between the Swedish and British setting and thereby draw conclusions regarding the Roman influence or lack of it in the Rural setting of Britain as well as the chosen settlements in Sweden. Was the Romanization of Britain for everyone or was it reserved for the elite

Flow evolution and mass transfer in a turbulent rectangular free jet of air with small laminar Schmidt number

Numerical results are presented for flow evolution, mass transfer and evaluation of the turbulent Schmidt number in a turbulent submerged free jet of air with small laminar Schmidt number (Sc = 0.1). A series of Large Eddy Simulation (LES) are carried on in the Reynolds number range from 5000 to 40,000. The numerical results are reported in terms of instantaneous and mean velocities, static pressure, passive scalar fields and turbulent Schmidt number. The numerical results show that the instantaneous cross-stream velocity and the static pressure are null in the Negligible Disturbance Flow (NDF) and the Small Disturbance Flow (SDF) of the instantaneous jet evolution, allowing a new definition of NDF and SDF. Similarly, the numerical mean static pressure is null in the Undisturbed Region of Flow (URF) of the mean evolution, allowing a new definition of URF. The turbulent Schmidt number shows differences at the two smallest Reynolds numbers, Re = 5000 and 10,000, in comparison to the previous numerical results, obtained with a laminar Schmidt number equal to Sc = 1. A theoretical model is proposed for the passive scalar diffusion in the Undisturbed Region of Flow (URF) and the Potential Core Region (PCR), under the hypotheses of self-similarity, according to the Tollmien and Görtler approaches. The solutions of the present theoretical models, at Sc = 0.1, are self-similar in the PCR and in good agreement with the LES numerical results of the passive scalar, while the passive scalar profiles are not self-similar in the URF at the smaller Reynolds numbers, differently from what happens with a laminar Schmidt number in the range 1–100. The theoretical model assumes a turbulent Schmidt number inversely proportional to the mean velocity gradient in the PCR, as suggested by the LES results. The numerical results of the ScT in the URF are variable in the range 0–0.85, which is a value commonly suggested in the literature. In the PCR the values of ScT are variable between zero and a maximum which is one order of magnitude greater than in the URF.</p

Numerical simulation of mass transfer and fluid flow evolution of a rectangular free jet of air

The paper presents Large Eddy Simulations (LES) of mass transfer and fluid flow evolutions of a submerged rectangular free jet of air in the range of Reynolds numbers from Re = 3400 to Re = 22,000, with the Reynolds number, Re, defined with the hydraulic diameter of the rectangular slot, of height H. The numerical simulations are 3D for Re = 3400 and 6800, while 2D for Re = 10,400 and 22,000 to reduce computational time costs. The average and instant LES numerical simulations are compared with the concentration visualizations, obtained with the Particle Image Velocimetry (PIV) technique, and the fluid dynamics variables, velocity and turbulence, measured with the PIV technique and the Hot Film Anemometry (HFA). In the numerical simulations, the Schmidt number is equal to 100 to compare the air concentration in the PIV experiments, while the turbulence on the exit of the slot is equal to the value measured experimentally, and ranging between 1% and 2%. The average 2-3D LES simulations are in agreement with the concentration and the fluid dynamics experimental results in the Undisturbed Region of Flow (URF) and in the Potential Core Region (PCR), while the vortex breakdown is captured only by the 3D LES approach. As far as the instant flow evolution is concerned, the 2-3D LES simulations reproduce the Negligible Disturbances Flow (NDF), where the jet height maintains constant, and the Small Disturbances Flow (SDF), where the jet height oscillates, with contractions and enlargements, but without the vortex formation. Average and instant velocity and turbulence numerical simulations on the centreline are in good agreement to the experimental PIV measurements

Experiments and numerical simulations of mass transfer and flow evolution in transient rectangular free jet of air

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.The paper investigates the transient flow evolution, up to the steady state, of a rectangular free jet of air with aspect ratio AR=6.3. The Reynolds number, Re, defined according to the hydraulic diameter, D, of the rectangular slot of height H, equal to about D=2H, spans in the range from Re=48,000 to Re=3400. A centrifugal fan generates the jet flow with a velocity increasing, as a ramp, from zero up to a constant steady state value. In the transient state of the flow the jet is composed of a primary vortex (PV) and a quasi-stable stem. In the transient 2D experimental instant images the stem of the jet has a height equal to that of the slot and a length increasing with the time up to a maximum value, which is greater than the lengths observed in the steady state, i.e. Negligible Disturbance Flow (NDF) and Small Disturbance Flow (SDF). The experimental jet evolution, observed with measurements and image processing, show that the primary vortex pinch-off does not occur for all the Reynolds numbers investigated, while the leading vortex structure becomes progressively incoherent and breaks down into turbulence. Two-dimensional (2D) Large Eddy Simulations (LES) of mass transfer and fluid flow evolution confirm the experimental images. The transient LES simulations are in good agreement with the experimental results

Numerical Simulation and Self-Similarity of the Mean Mass Transfer in Turbulent Round Jets

The paper investigates the mean mass transfer/passive scalar spreading in turbulent submerged round jets. Two regions of flow are present in the jet evolution: the Near-Field Region (NFR) and the Fully Developed Region (FDR). This group of research investigates from some years the mean evolution of turbulent rectangular jets with the new physical finding that two sub-regions (not a single one) are present in the NFR. The first region of the two is the newly discovered Undisturbed Region of Flow (URF), while the second one is the known Potential Core Region (PCR). In a recent paper we showed that the flow evolution of turbulent round jets, as far as momentum spreading is concerned, is self-similar also in the NFR. Literature shows that mass transfer spreading is self-similar only in FDR. The present paper presents new mean mass transfer results of the numerical Large Eddy Simulation (LES) in turbulent round jets. Four Reynolds numbers, from 2492 to 19,988, and two laminar Schmidt numbers, 1 and 10, are investigated. The first novel result of this paper is that mass transfer is self-similar in the NFR. The second result is that two new analytical models describe the passive scalar spreading in the URF and PCR. The third result is that two new self-similar laws describe the passive scalar spreading in the FDR. The fourth result states that the well-known power-law relationship, between passive scalar and axial momentum in the FDR, holds regardless of the modeling of turbulent viscosity and turbulent Schmidt number

Further results on the mean mass transfer and fluid flow in a turbulent round jet

The present paper reports new numerical results of the mean mass transfer in a turbulent submerged round jet. A series of Large Eddy Simulations (LES) are presented at four Reynolds (Re) numbers (Re = 2492, Re = 4491, Re = 9994, Re = 19,988) and laminar Schmidt (Sc) number equal to Sc = 10. The numerical results are specially focused on their patterns in the Undisturbed Region of Flow (URF), Potential Core Region (PCR) and Fully Developed Region (FDR). The present results are compared with the previous literature concerning a two-dimensional and a three-dimensional jet, issuing from an infinitely wide slot, with the conclusion that the turbulence moments decay faster in a round jet configuration.</p