Jet (fluid dynamics)

“ That the jet we now see should be directed downwards rather than upwards may, I think, be explained in a general way as follows:—The great initial momentum of the sphere causes it to continue in rapid motion after the bubble has closed, thus the sphere acts as a sort of piston, which by increasing the length of the air-tube diminishes the pressure in it and so sucks in the bubble, which is driven down by the greater atmospheric pressure above. ”

“ Natural sources of water are also used for compressing and discharging air by letting the water under its natural pressure enter and leave closed vessels, so alternately discharging and drawing in new supplies of air. Here the action is the same as in a blowing engine, the water taking the place of the piston. This method was first thoroughly developed in connexion with the Mt. Cenis tunnel works, and its use has since been extended.
In the jet blower (fig. 9) a jet of steam is used to induce a current of air. ”

“ Suddenly the water begins to rise in the well, overflowing till it fills the basin. Loud explosions are heard from below, and the ground trembles. Then, with amazing violence, up springs a vast column of boiling water, surmounted by clouds of steam, which obscure the air. This first jet is followed by several others in rapid succession, to the number of sixteen or eighteen; the last jet being usually the greatest of all, and attaining a height of nearly a hundred feet. In some instances it has risen to a height of a hundred and fifty feet ”

“ The steam breath gradually grows and is exhaled with more vigor. Presently he belches up a barrel or so of water which falls back into his throat. Then in a minute come two or three such little spasms, when up lifts a rounded column two or three feet in diameter, rising higher and higher in exact perpendicularity 150 feet high. The jet breaks more or less as it rises into pointed sprays, which, when there is no wind blowing, fall with almost precise regularity about the up going column. ”

“ The jet plane carries no oxygen for its engine: its jet propulsion engine uses oxygen from the air. This engine has fewer parts and is of simpler construction than the traditional engine. It operates a mechanism which compresses the air. This air is mixed with atomized fuels such as gasoline, kerosene, alcohol, or some other fuels of the hydrocarbon family, rich in hydrogen. From that point forward the operation is the same as in the rocket engine; that is to say, the gas is released and ignited, the resulting expansion and emission through the jet providing the power.... ”

“ If water be forced upwards through a vertical tube (with a nozzle one-twentieth of an inch in diameter) , it will fall to the ground in a fine rain; but, if a piece of rubbed (electrified) sealing-wax be held a yard distant from the place where the jet breaks into drops, they at once fall in large spots as in a thunder-shower. If paper be put on the ground during the [Pg 84] experiment, the sound of pattering will be observed to be quite different. If a kite be flown into a cloud, and made to give off electricity for some time, that cloud will begin to condense into rain. ”

“ If we leave the resistance of the air out of consideration, the water in the horizontal jet has no obstacle to overcome; and it might go on for ever, if its weight did not gradually cause its path to become more and more bent towards the earth, against which it eventually strikes.
When the jet is vertical the case is altered. The water thrown up vertically constantly tends to fall down vertically, as any other heavy body would do, and its momentum has to overcome the obstacle of its gravity. ”

“ With this jet there is little or no danger of the jet 'snapping' out through a surplus of oxygen, as the greater the flow of this gas, the greater the suction on the coal gas side.
The light is not quite equal to a good mixed jet, but very nearly so, and therefore this jet is deservedly gaining in favour every day. ”

“ If we gradually increase the velocity with which a well-polished sphere enters the liquid we find that there is a gradual transition from the silent "smooth" or "sheath" splash taking down no air and giving rise to only an insignificant column, to the noisy, "rough," "basket" splash taking down much air and throwing up a tall and conspicuous jet. Thus in the fourth figure of Series XI, in which the height of fall has been increased from 15 to 60 cm. ”

“ The steam thrown into the air is nearly all condensed into little drops which fall back, and this condensation and this fall represent simply the loss of something, an interruption, a deficit. But a small part of the jet of steam subsists, uncondensed, for some seconds; it is making an effort to raise the drops which are falling; it succeeds at most in retarding their fall. So, from an immense reservoir of life, jets must be gushing out unceasingly, of which each, falling back, is a world. ”

“ All one has to do is to insert in the balloon model a little tube to furnish a jet of the room's atmosphere from an air pump and light it with the electric spark. Similarly, should a pin-prick have made ever so slight a vent in my air-ship balloon, the interior pressure would have sent out into the atmosphere a long thin stream of hydrogen that might have ignited had there been any flame near enough to do it. ”

“ As we rise, the air becomes thinner. Finally a point is reached at which no propeller will ‘bite.’ The ceiling has been attained.
“With jet propulsion, exactly the opposite holds good. The less air there is, the more efficient is the motor. If the ejected gas has an expansion efficiency at rest of 40 feet in one-hundredth of a second—a rate of 4,000 feet a second—the same force exerted in motion would increase the speed up to a point where the maximum efficiency is reached at something like 10,000 miles an hour. Jet propulsion gets better and better as speed and height increase. ”

“ The mingling of the wake and counterwake may be regarded as a phenomenon quite apart from the initial disturbance, and the turbulence or otherwise of the wake does not materially add to or detract from the pressure on the front face of the body, but concerns merely the ultimate disposal of the energy left behind in the fluid. ”

“ As soon as the fourth jet was thrown out, which was much less than the former, and scarcely at the interval of two minutes from the first, the water sunk rapidly in the basin, with a rushing noise, and nothing was to be seen but the column of steam, which had been continually increasing from the commencement of the eruption, and was now ascending perpendicularly to an amazing height, as there was scarcely any wind, expanding in bulk as it rose, but decreasing in density, till the upper part of the column gradually lost itself in the surrounding atmosphere. ”

“ Sometimes, instead of shovelling the earth into the troughs, it can be washed out of its position into suitable channels by means of a powerful jet of water. This mode of working, which is termed hydraulic jet sluicing, offers great advantages where the natural conditions admit of its adoption. ”

“ An analysis of the flight recorder of the jet which departed New Orleans immediately after Flight 304 substantiates the severity of the turbulence in the area. Accelerations to +0.2 and +1.9-g between 2,000 and 6,000 feet, recorded on this tape, indicate severe turbulence. Since known or forecast turbulence along the climb path is the prime criterion for selection of the climb speed, it is probable that the crew of Flight 304, unconcerned about turbulence below 14,000 feet, chose 310 knots rather than the lower rough airspeeds depicted in their flight manual. ”

“ If to a vertical pipe we adapt a horizontal one that revolves with a certain velocity, and throws out water horizontally, it will be understood that, from a bird's eye view, the jet will form a spiral. Each drop of water will recede radially in space, the spiral will keep forming at the jet, and if, through any reason, the latter alone be visible, we shall see a nearly rectilinear jet that will seem to revolve with the pipe. ”

“ When a water jet serves as collector, the pressure under which it issues should be practically constant. If the pressure alters as the water tank empties, a discontinuity occurs in the trace when the tank is refilled, and a fictitious element may be introduced into the diurnal variation. When rain or snow is falling, the potential frequently changes rapidly. ”

“ Hence, as the vat empties, the jet becomes shorter and shorter, until at last it sinks down to nothing.
The energy of moving water makes it, under some circumstances, one of the most destructive of natural agents; and, under others, one of the most useful servants of man. ”

“ Rough sphere falling 60 cm. Scale 3/4.
[pg 88] Thus the first three figures of Series VIII show the last moments of a bubble which has burst, spontaneously, and so has made way for the jet of Fig. 3. (These are taken from a splash into petroleum with 24·5 cm. fall.) But the last two figures, 4 and 5 (taken with a 32 cm. fall) , show how a bubble which might otherwise have been permanent, is stabbed by the rising jet and destroyed. With water and 60 cm. fall the jet appears sometimes to rise quite unimpeded, and sometimes to be checked by the still closed bubble. ”

“ The Cow displayed the answer, six hundred forty pounds of thrust.
"O.K.," said Mike. "Thanks." Then to the captain and the scientist and Security officer who were waiting beside him: "The puncture is obviously small enough to serve as a jet, rather than to have let the nitrogen out in one whoosh, since that would have given you far more than six hundred forty pounds of thrust. Therefore, it will probably be quite simple to patch the hole.
"Nitrogen is obviously escaping, but it wouldn't be worth a man's life to send him out into that flare-storm to patch it. ”

“ Some years ago experimental water-jet vessels were built in New York in which a jet only 5⁄8 inch in diameter with a pressure of 2,500 pounds per square inch was used, but the experiment proved a failure. The propelling force of a jet is the reaction of the stream of water against the orifice from which it issues. The action is just like Hero’s reaction steam turbine referred to on page 143. The propulsion would be the same were the jet discharged in the open air or in a vacuum or against a solid stone wall. ”

“ One reason for this is that the air flows out of the choke tube faster than it flows into it, owing to the fact that its volume increases as the pressure decreases, and hence the pressure round the jet falls very rapidly indeed as the air velocity increases and causes too much petrol to issue from the jet in proportion to the quantity of air flowing through the tube.47 The choke tube is often a plain piece of pipe, as shown in Fig. ”

“ Otherwise, both power and communications would have been lost.
A system of gas jets and valves was used periodically to adjust the attitude or position of the spacecraft. Expulsion of nitrogen gas supplied the force for these adjustments during the cruise mode. ”

“ But there is no conduit to carry away the efflux air, which consequently passes into and becomes mixed up with the turbulent dead-water; and the efflux air carries with it its momentum, which is communicated to the dead-water, and momentum communicated to the dead-water appears as negative pressure on the rear face of the plane, since it is the plane itself that prevents the dead-water from being washed bodily away. ”

“ The effects of torrential rains in high winds of the storm are simulated in this manner. After every flight, the plane needs very thorough examination. One of the troubles is that salt air at high speed causes rapid corrosion. Salt may accumulate around the engines. Also, severe turbulence causes damage to the plane.
After the take-off, the pilot and co-pilot can see what is ahead most of the time, but for considerable intervals they are on instruments, or, as they say in the Navy, “on the gauges.” ”

“ A wind of twenty-five miles an hour, or what sailors would call a good stiff breeze, travels 39·67 feet per second, and exerts a pressure of from 2·208 to 3·075 pounds per square foot. The prodigious energy of a hurricane, traveling not infrequently at the rate of one hundred miles per hour, is too well known by its disastrous effects to need repetition. The power of the wind, however, save for ship-propulsion, is utilized in but few situations, its unreliability having caused it to be but very slightly esteemed in comparison with water-power and steam. ”

“ Overhead and projecting from beyond the point of the nacelle was the blunt nose of the gas-bag, the port side tinted a rosy red as the growing light glinted on it, the starboard side showing dark grey against the sombre sky. A thousand feet below were rolling masses of clouds, their nether edges suffused by dawn. Between the rifts in the bank of vapour was apparently a black, unfathomable void, for as yet the first signs of another day were vouchsafed only to the airman flying far above the surface of the sea. ”

“ A connected mass of 27,000 tons is not as easily heaved as a cork or a cockle-shell; but the storm-winds and the storm-waves of the open ocean have a tremendous power. What will they do then, with this stupendous morsel, when they have it fairly within their clutches? The heaviest hurricane-wind blows with a force that would act upon a square foot of resisting surface with a pressure equivalent to a weight of 40 lb. Such a wind could only heel the leviathan with its full load out of the perpendicular to the extent of six inches even if it struck it quite on the side! ”