Wyniki wyszukiwania - Biblioteka Nauki

1

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

100%

Orizaga S. , Riahi D. N.

Journal of Theoretical and Applied Mechanics

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2012

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tom 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.

2

Sharp-crested weir head losses investigation

100%

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

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tom 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

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

86%

Habib M. , Rachid S. , Ismail D.

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2022

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tom 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.

4

Microclimate Thermal Control for Open-Air Areas

72%

Beithou N. , Khalid M. B. , As’ad S. , Attar H. , Al-Khawaldeh M. A. , Borowski G. , Rababa K. S. , Andruszkiewicz A. , Alsaqoor S.

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2024

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tom Vol. 25, iss. 5

198--207

EN

Thermal comfort in openair situations is a difficult industrial task. In literature there were insufficient studies on how to control the external microclimate in a region, and there are many activities outside the house in open areas that require temperature control, such as the stadiums in hot humid countries, and tourism, and recreational areas in humid and hot climates. Openair conditioning requires huge amount of energy, that negatively affects the global warming of the earth. To reduce energy consumption microclimate control is proposed. Isolation of the controlled area is performed to reduce the amount of air-conditioned load. In this project the air conditioning of an external open area will be studied. Wind tunnel with two air flows at different temperatures, relative humilities, angle of attach and velocities will be constructed. The two flows will be allowed to intersect to gather at different conditions (different wind speeds ranging from 1 to 7 m/s, as well as a jet flow about 1 m/s and angles 60 to 90 degrees) to construct an isolation Dom for the targeted outside open area. An open area with the use of cross flow that stops the local wind speed in the targeted area and allows to keep the conditioned air for a long time in the open space. This method allows to save huge energy used continuously for the air-conditioning purpose.

5

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

72%

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

International Journal of Applied Mechanics and Engineering

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2002

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tom 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.