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1

Effect of the inner diameter and Reynolds numer on the recirculation zone in annular jet flow

Habib Merouane, Rachid Sahnoun, Ismail Drai

International Journal of Applied Mechanics and Engineering

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2022

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Vol. 27, no. 2

87--97

EN

In this paper, we focus on the effect of the inner diameter and Reynolds number on the recirculation zone in an annular jet flow with numerical simulation by resolving the Reynolds-averaged Navier-Stokes equations with the first closed model of turbulence k-epsilon. The annular jet plays an essential role in stabilizing the flame in the burner which is used in many industrial applications. The annular jet is characterized by the inner and outer diameter. In this study, three different inner diameters are adopted with constant width of the annular jet. We adopted also three different values of the Reynolds number show the effect of the Reynolds number on the recirculation zone. The simulation is realized by a CFD code which uses the finite element method. The results obtained from this study are in good agreement with the experimental data. Two recirculation zones are shown; a large recirculation zone at the outlet of the flow and a small recirculation zone just near the injection generated by the annular flow and the inner diameter ;iD it is observed that the size of the recirculation zone increases when the inner diameter increases and the length of the recirculation zone depends only on the inner diameter. This recirculation zone is also affected by the Reynolds number with a very low variation of the recirculation length.

2

Sharp-crested weir head losses investigation

Korniichuk V., Khlapuk M., Bezusyak O., Yasinska L.

Czasopismo Inżynierii Lądowej, Środowiska i Architektury / Journal of Civil Engineering, Environment and Architecture

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2018

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z. 65, nr 1

27--34

EN

The work is devoted to the rectangular sharp-crested weir calculation methods improvement. This can be realized by using mathematical model developed on energy and momentum conservation principles. In order to get energy conservation equation within sharp-crested weir we have to know weir head losses. This article presents theoretical and experimental investigations of the sharp-crested weir head losses. The height of the weir plate pw and weir head H are estimated as main operating factors that determine hydraulic weir outbound parameters: threshold depth h and the specific weir flow q. The flow moving over sharp-crested weir suffers sudden vertical contraction and transforms from the uniform flow to a jet. Mentioned above, causes sharp-crested weir head losses. To determine these losses, we propose to use Hind’s formula that describes similar contraction losses in the channel. Experimental investigations proved Hind’s formula application adequacy to evaluate these losses. Sharpcrested weir energy conservation equation that includes head losses is determined. Graphs set out in the article disclose the influence of the main operating factors and their ratio on the relative head losses.

3

On combined spatial and temporal instabilities of electrically driven jets with constant or variable applied field

Orizaga S., Riahi D. N.

Journal of Theoretical and Applied Mechanics

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2012

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Vol. 50 nr 1

301-319

EN

We investigate the problem of combined spatial and temporal instabilities of electrically driven viscous jets with finite electrical conductivity in the presence of either constant or variable applied electric field. A mathematical model leads to a lengthy equation for the unknown spatial growth rate and temporal growth rate of the disturbances. This equation is solved numerically using Newton’s method. We investigated two cases of water jets and glycerol jets. For water jets and in the case of either constant or variable applied field, we found two new modes of instabilities which grow simultaneously in time and space and lead to significant reduction in the jet radius. However, in the case of glycerol jets, we found two new modes of instabilities in the presence of constant applied field but only one mode of instability in the presence of variable applied field. For the glycerol jets, the combined temporal and spatial instabilities are less stronger and lead to an increase in the jet radius. The instabilities for both types of water and glycerol jets were found to be restricted to particular domain in their wavelength and were enhanced with the strength of the electric field.

PL

Autorzy prezentują problem złożonych przestrzenno-czasowych niestabilności elektrycznie indukowanych strumieni wiskotycznych o skończonej przewodności elektrycznej w obecności stałego albo zmiennego pola. Model matematyczny sprowadzono do skomplikowanego równania, w którym niewiadomą jest czasowe i przestrzenne tempo wzrostu zakłóceń w strumieniu. Równanie to rozwiązano numerycznie, używając metody Newtona. Zbadano dwa przypadki – dla strumienia wody i gliceryny. Dla wody, niezależnie od tego, czy pole elektryczne jest stałe, czy zmienne, wykryto dwie nowe postacie niestabilności rosnących równocześnie w czasie i przestrzeni, które znacznie ograniczają promień strumienia. W przypadku gliceryny, dwie nowe postacie niestabilności znaleziono tylko przy stałym polu elektrycznym. W polu zmiennym zaobserwowano jedną postać. Dla gliceryny, złożone niestabilności przestrzenno-czasowe wykazują słabszą intensywność i zwiększają promień strumienia. Niezależnie od rodzaju ośrodka, niestabilności te ograniczają się do pewnego zakresu długości falowej i wzrastają z natężeniem pola elektrycznego.

4

An investigation of the shear and pressure flows interaction in a hydrostatic journal bearing pocket

Braun M. J., Peloso D., Daniels C. C.

International Journal of Applied Mechanics and Engineering

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2002

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Vol. 7, no 3

739-747

EN

The present paper studies parametrically the flow patterns and pressure profiles inside of, and on the adjoining seals of a single hydrostatic pocket, characteristic component of hydrostatic journal bearings. The major focus is on the interaction between the effects of the shear flow (Couette) created by the rotation of an eccentric shaft and the pressure induced flow due to hydrostatic jet penetrating at the bottom of the pocket. The pocket is square in nature with a size of 17.8mm x 17.8mm footprint. Its bottom surface has a radial sliding capability, such that the depth of the pocket can be changed, without breaking pocket integrity. This construction allows the study and ensuing comparison of the influence of changes in clearance, jet strength and shaft angular velocity on the flow patterns, pressure profiles and the combined hydrostatic and hydrodynamic effects. The flow structure of the jet and its interaction with the flow in the pocket itself is visualized qualitatively using long distance microscopy (up to x400). The PIV system used herein is equipped with a digital video-camera and a pulsing laser (30mJ/pulse) with a repetition capability of up to 5000Hz.

5

Large eddy simulation of a single jet flow in highly preheated and diluted air combustion

Dong W., Blasiak W.

Archivum Combustionis

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2000

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Vol. 20 nr 3-4

163-176

EN

In the present work, the large eddy simulation (LES) has been used to simulate a single fuel jet reacting flow under the conditions of highly preheated and diluted air combustion (HPDAC). A hybrid procedure of the standard subgrid scale (SGS) magorinky-Lille model and Reynolds stress model (RSM) together with the finite rate/eddy dissipation reaction model has been employed to simulate a single wall jet HPDAC furnace chamber. The propane-air two-step combustion system is selected for modeling under two different HPDAC inlet air conditions corresponding to 3% w/w oxygen at 1300K and 21% w/w oxygen at 1300K. The numerical results show that the standart Smagorinsky model and Reynolds stress model together with the finite rate/eddy disspation model are capable of predicting the global flame effects on the flow, such as flow velocities, mixing patterns, temperatures and turbulent parameters. The predictions are found in acceptable agreement with the corresponding results of in-furnace measurements and physical modeling. By compared with the pure Reynolds stress model, it is found that the differences between the two predictions of LES and RSM are insignificant in the near field of the flow. The Smagorinsky constant C, has been also tuned in the work. It illustrates that Cs value significantly influences the predictions on both near field and far of the jet flow. Though, further development of SGS stress and combustion models is needed, it is found that LES is an attratctive tool to simulate the dynamic processes of turbulent reacting flows for the HPDAC furnaces.