Zhitao Yan, Yongli Zhong, William E. Lin, Eric Savory and Yi You
This paper examines various turbulence models for numerical simulation of a steady, two-dimensional (2-D) plane wall jet without co-flow using the commercial CFD software (ANSYS…
Abstract
Purpose
This paper examines various turbulence models for numerical simulation of a steady, two-dimensional (2-D) plane wall jet without co-flow using the commercial CFD software (ANSYS FLUENT 14.5). The purpose of this paper is to decide the most suitable and most economical method for steady, 2-D plane wall jet simulation.
Design/methodology/approach
Seven Reynolds-averaged Navier–Stokes (RANS) turbulence models were evaluated with respect to typical jet scaling parameters such as the jet half-height and the decay of maximum jet velocity, as well as coefficients from the law of the wall and for skin friction. Then, a plane wall jet generating from a rectangular slot of 1:6 aspect ratio located adjacent to the wall was investigated in a three-dimensional (3-D) model using large eddy simulation (LES) and the Stress-omega Reynolds stress model (SWRSM), with the results compared to experimental measurements.
Findings
The comparisons of these simulated flow characteristics indicated that the SWRSM was the best of the seven RANS models for simulating the turbulent wall jet. When scaled with outer variables, LES and SWRSM gave generally indistinguishable mean velocity profiles. However, SWRSM performed better for near-wall mean velocity profiles when scaled with inner variables. In general, the results show that LES performed reasonably well when predicting the Reynolds stresses.
Originality/value
The main contribution of this article is in determining the capabilities of different RANS turbulence closures and LES for the prediction of the 2-D steady wall jet flow to identify the best modelling approach.
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Ran Bi, Shady Ali, Eric Savory and Chao Zhang
This study aims (1) to numerically investigate the characteristics of a human cough jet in a quiescent environment, such as the variation with time of the velocity field…
Abstract
Purpose
This study aims (1) to numerically investigate the characteristics of a human cough jet in a quiescent environment, such as the variation with time of the velocity field, streamwise jet penetration and maximum jet width. Two different turbulence modelling approaches, the unsteady Reynolds-averaged Navier–Stokes (URANS) and large eddy simulation (LES), are used for comparison purposes. (2) To validate the numerical results with the experimental data.
Design/methodology/approach
Two different approaches, the URANS and LES, are used to simulate a human cough jet flow. The numerical results for the velocity magnitude contours and the spatial average of the two-dimensional velocity magnitude over the corresponding particle image velocimetry (PIV) field of view are compared with the relevant PIV measurements. Similarly, the numerical results for the streamwise velocity component at the hot-wire probe location are compared with the hot-wire anemometry (HWA) measurements. Furthermore, the numerical results for the streamwise jet penetration are compared with the data from the previous experimental work.
Findings
Based on the comparison with the URANS approach and the experimental data, the LES approach can predict the temporal development of a human cough jet reasonably well. In addition, the maximum width of the cough jet is found to grow practically linearly with time in the far-field, interrupted-jet stage, while the corresponding axial distance from the mouth of the jet front increases with time in an approximately quadratic manner.
Originality/value
Currently, no numerical study of human cough flow has been conducted using the LES approach due to the following challenges: (1) the computational cost is much higher than that of the URANS approach; (2) it is difficult to specify the turbulent fluctuations at the mouth for the cough jet properly; (3) it is necessary to define the appropriate conditions for the droplets to obtain statistically valid results. Therefore, this work fills this research gap.
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Generally speaking a “new” loaf is demanded and the baker who cannot deliver “new” loaves loses trade. But what is a “new” loaf? From the point of view of the chemist this…
Abstract
Generally speaking a “new” loaf is demanded and the baker who cannot deliver “new” loaves loses trade. But what is a “new” loaf? From the point of view of the chemist this question has formed the subject of innumerable investigations. A definition of a “new” loaf demands an understanding of “staleness” and the staling of bakery products is a subject of great complexity. The old idea was that it was entirely a question of the “drying out” of the bread, but cereal chemistry has proved that such a solution, namely the prevention of “drying out,” is only of partial efficacy; in fact “staleness” is caused by a change in the starch of the flour which is inherent in it and cannot be prevented by precautions which maintain the moisture content at a certain figure. The investigation of this type of staling has occupied the attention of many famous chemists, but the full explanation has not yet been obtained. Mass production has demanded many studies in that aspect of science known as “physical chemistry.” An example can be found in the preparation of certain sauces. Those of you who have made mayonnaise sauce know that to beat the olive oil into the mixture is fraught with difficulties. By means of the fork, used as a beater, the oil is distributed in very small particles through the mass of liquid, so that every globule of oil is separated from every other one. If the action docs not proceed properly the system breaks down and the mayonnaise “turns” and is spoiled. The manufacturer has to prevent this “turning,” not in a few pints but in hundreds of gallons. It is the chemist who has enabled him to do this and to manufacture with success those scores of salad‐dressings which are so delectable and the purchase of which relieves the housewife of so many hours of work and so much arm‐ache. An example of some interest is concerned with smoked salmon, which normally is a very variable product, whether it be the highly salted variety of the northern climes or the much less salted kind which has found favour in this country. The production of a lightly salted product is far more difficult than the more salted variety because much smaller changes in salt content become more noticeable. These small differences are so obvious to the confirmed smoked salmon eater that he detects not only the differences between one grade and another, but also the differences of salt content that occur in different parts of the same side of fish. It has fallen to the chemist so to change the methods of production of the lightly flavoured variety that the distribution of salt through the fish is even and the flavour therefore constant. This study of smoked salmon is only an example of the very big problem of standardisation, standardisation demanded by the consumer—and it follows that the big manufacturer must produce goods of standard flavour and appearance. Science steps in and gives the manufacturer those controls which enable him to produce, day in and day out, that standard range of article, whether it be ice‐cream or toad‐in‐the‐hole, Worcester sauce or cheese cakes, roast beef or jelly crystals. Modern science has introduced a new factor into our conception of what food should be. In the past it was only necessary to ensure that food should be “pure and wholesome,” by which was meant—in general terms—digestible and without any harmful constituents, be they natural or adventitious, bacterial or otherwise. So long as food complied with this broad definition everyone was satisfied. But biochemists and physiologists have demonstrated the importance of other factors, salts and vitamins, and it is necessary to consider the new situation thus created because it may be that the treatment of food to retain those substances may make it necessary to change preconceived notions. It may be that “palatability” may be affected, palatability which includes taste and appearance and odour. The whole subject is so complicated and, notwithstanding the enormous amount of work carried out, so little understood that no one as yet can be dogmatic, no one can state what are the optimum amounts of vitamins required by ordinary persons to keep them in good health. Having, however, decided the amount required, are we to try to preserve such quantities as occur naturally, or are we to fortify the food which we cat by added synthetic or even by purified natural vitamins? A further important consideration is whether the degree of maturity of, say, fruit in relation to maximum vitamin content coincides with optimum palatabilty. Certain it is that information gradually being accumulated on the importance—in many cases vital importance—of the minor constituents of foodstuffs leads to the conclusion that, to ensure the presence of all valuable minor constituents—be they known or unknown—the foodstuffs must, as articles of diet, be ingested almost in their entirety. This is probably an extreme view, for, in many cases, the result would be a product of reduced palatability or appearance, or, what is probably more important, “different,” and people do not like their food to be abnormal, i.e., to differ from their preconceived notion of what it should be. Nevertheless an “improvement” in the method of production, put into practice by the food manufacturer with the best intentions, may possibly result in a lowering of the dietetic value of the food, as, for example, by mechanical removal of an important part (the classical example being polished rice), by heat treatment, by oxidation or by materials added during cooking. The minor metallic constituents of food are gradually being revealed in their true importance. Copper, zinc, and iron are now known to be of importance. It is probable that every baby is born poor in calcium but rich in iron; milk, the natural food of the infant, is rich in calcium. It is only in the last few years that it has been shown that green vegetables as usually cooked are of very little real value. Cooking green vegetables in water containing sodium carbonate results in the almost complete destruction of the Vitamin C, and the discarding of the water removes the extracted salts. A green product certainly results but of greatly reduced nutritional value. On the other hand, it would appear that little destruction of vitamin activity takes place when the canning of vegetables or fruits is properly controlled. Sherman has said that attention to mineral salts and vitamins will lead to “buoyant” as distinguished from merely “passable” health. It is obvious that education of the public is essential if an intelligent use is to be made of the knowledge being gained by chemists and allied scientists. It is a most important fact that methods are being developed to assay foods for vitamins by chemical means. Biological feeding tests are obviously unsuitable for control purposes but, as the chemical identity of the vitamins becomes more clarified, chemical tests will become available for their determination. It is obviously the duty of the medical services of the country to guide the public as far as is possible on questions of nutrition. When such guidance becomes effective, the food producer will not be slow to see that his goods are up to the standard necessary, adding one more burden to the already loaded back of the chemist concerned with food production.
One of Her Britannic Majesty's Ministers hanging about outside the Council Chamber while it is deliberated within whether or not Britain is to be admitted to the not so Common…
Abstract
One of Her Britannic Majesty's Ministers hanging about outside the Council Chamber while it is deliberated within whether or not Britain is to be admitted to the not so Common Market must present a picture never‐to‐be‐forgotten. Public officers, of course, are accus‐tomed to this when attending selection interviews for appointments, but such experiences invariably make us feel a little like “poor relations.” The controversy of whether we are “in” or “out” then is settled—and we must be under no delusions—for a very long time. As we see it, the French want the densely populated area of Western Europe as an agricultural market for themselves alone. They appeared to be willing to let Denmark in, but they have no intention of letting Britain in to bring the vast Commonwealth agricultural exports with them, via the back door, so to speak. That is the position now and even when “all the kings depart”, it will not change.
The total number of samples which were submitted under the Food and Drugs Act was 2,063. Of these, 5·7 per cent were adulterated or incorrect. Of these, 1,062 were milks, with 7·5…
Abstract
The total number of samples which were submitted under the Food and Drugs Act was 2,063. Of these, 5·7 per cent were adulterated or incorrect. Of these, 1,062 were milks, with 7·5 per cent reported against. The percentage was 104 in 1947 but “ it is still high ”. The composition of the milk for the years 1939 and 1945–8 (figures given) was constant “ in spite of the difficulties of obtaining feeding stuffs ” and of good quality. No preservatives were found in the samples examined. The prosecutions were due to fat deficiency or to added water. The offences were not deliberate in all cases.
The analyses of trends in prosecutions under the Food and Drugs Act, 1955 and the various regulations, which we have prepared every two years or so, covering a three‐month period…
Abstract
The analyses of trends in prosecutions under the Food and Drugs Act, 1955 and the various regulations, which we have prepared every two years or so, covering a three‐month period, have been so much appreciated by readers, both in the administration and the industry itself, that we have prepared a more extended survey, covering the whole of 1966. The survey, as before, takes the form of a month‐by‐month analysis of reports of legal proceedings received by us from all parts of the country, and as formerly records the prosecutions under similar groupings; cases under Section 2, subdivided into those relating to compositional offences, the presence of foreign bodies and those relating to mouldy food: false description cases under Section 6 of the Merchandise Marks Acts; Section 8, the unfit food provision, also subdivided with special categories for foreign bodies and mouldy food; Section 32, milk cases; cases under the Food Hygiene Regulations, 1960, with smoking offences separated; the Milk and Dairies Regulations, consisting almost entirely of prosecutions under Reg. 27, Meat Regulations, Preservative Regulations, Colouring Matter in Food Regulations, etc.
The management of children′s literature is a search for value andsuitability. Effective policies in library and educational work arebased firmly on knowledge of materials, and on…
Abstract
The management of children′s literature is a search for value and suitability. Effective policies in library and educational work are based firmly on knowledge of materials, and on the bibliographical and critical frame within which the materials appear and might best be selected. Boundaries, like those between quality and popular books, and between children′s and adult materials, present important challenges for selection, and implicit in this process are professional acumen and judgement. Yet also there are attitudes and systems of values, which can powerfully influence selection on grounds of morality and good taste. To guard against undue subjectivity, the knowledge frame should acknowledge the relevance of social and experiential context for all reading materials, how readers think as well as how they read, and what explicit and implicit agendas the authors have. The good professional takes all these factors on board.
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At every period of time marked by years, the seasons by turns and twists in history, among country folk especially, the years of great storms and hard winters; in law enforcement…
Abstract
At every period of time marked by years, the seasons by turns and twists in history, among country folk especially, the years of great storms and hard winters; in law enforcement, the passing of some far‐reaching, profound statutory measure, there is this almost universal tendency to look back—over your shoulder‐assessing changes, progressive or otherwise, discerning trends and assaying prospects. We are about to emerge from the seventies—battered but unbowed!—into the new decade of the eighties, perhaps with a feeling that things can only get better.
There have always been traditional differences between the various regions of the British Isles. For example, meat consumption is greater in the North than the South; most…
Abstract
There have always been traditional differences between the various regions of the British Isles. For example, meat consumption is greater in the North than the South; most families take some meat at every meal and this extends to the children. The North is the home of the savoury meat products, eg., faggots, rissoles and similar preparations and a high meat content for such foods as sausages is expected; between 80 and 90% with the cereal only present for binding purposes. Present minimum meat contents would be considered a swindle, also the nature of the lean meat and the lean meat/fat ratio. The high water content similarly would have been unacceptable.
Difficulties which have for many years surrounded the interpretation of false descriptions of trade goods and services are emphasised in the discussions, in and out of Parliament…
Abstract
Difficulties which have for many years surrounded the interpretation of false descriptions of trade goods and services are emphasised in the discussions, in and out of Parliament, of the Protection of Consumers (Trade Descriptions) Bill, the new code of consumer legislation which although incorporating much that has gone before, does introduce a number of rather sweeping extensions. In the opening of the Committee stage in the House of Lords most of the debate ranged around the meaning of the term false description itself, and an amendment which defeated the Government, made it necessary for a description to be false in a material particular to be an offence. This is in fact the present law. The amendment has now little more than theoretical interest as the Bill with numerous others was jettisoned because of the General Election.