Vertical downward turbine surface aerator

Abstract

Vertical downward turbine surface aerator: Unlike current aerators, which are either upward-moving or side-discharge turbines, this one generates a cloud of air bubbles beneath the machine without cavitation. The process relies on generating a specific conical turbulence with an opening of 30 to 40 degrees, which, while drawing the required quantity of air bubbles to a precise depth, keeps them sufficiently away from the hydraulic blades. Figure 1.This aeration machine comprises three distinct elements that allow for the sequencing of the process: a purely hydraulic turbine generating conical turbulence with an opening of approximately thirty to forty degrees; an air injection system based on a centrifugal effect, delivering the precise quantity of air in the form of calibrated bubbles at the apex of the aforementioned cone; and finally, an anti-cavitation system that isolates the propeller from the surface and traps any bubbles that could cause cavitation. The combination of these three elements is essential and characteristic of the process. The integration of these three elements eliminates cavitation, resulting in significantly higher efficiency due to the absence of water lift, as gas exchange is enhanced by the extended transit time of the air bubbles through the water.

Description

Title of the invention: Surface aerator with downward vertical turbine

[0001] The present innovation relates to a hydraulic system intended to equip either our system under number FR2000351 of 16 / 07 / 2021, or to operate autonomously in bodies of water.

[0002] Unlike existing systems which are either upward-moving turbines - the water being raised - or lateral-moving turbines - the water mixed with air bubbles having to be kept away from the turbine to prevent any cavitation - the process which will be described allows the injection of a water / air mixture vertically for oxygenation purposes.

[0003] The process is based on the sequencing of the different operations, by juxtaposing three distinct elements integrated into the same machine.

[0004] The origin of the cavitation prohibiting the "vertical" use of the machines currently on the market is due above all to the process used to include the air in the water: namely a venturi.

[0005] To create a venturi, the water must be accelerated strongly, then directed into an enclosure where it decelerates abruptly in the presence of air, this enclosure being able to be replaced by a strong convergence of the turbulence generated by the turbine blades, resulting in the creation of a shear zone where air is introduced.

[0006] This process induces several problems such as the generation of a narrow and violent current from which the bubbles escape rapidly (therefore in the immediate vicinity of the turbine which they cause to cavitate), but also the generation of bubbles of all sizes — the strong shear zone causing the larger ones to break into smaller bubbles; finally the air supply vent must be located immediately downstream of the blades, which causes an upwelling of air in the micro-turbulences inevitably present at this location — hence a strong degradation of the performance of the turbine and the creation of very small bubbles which remain suspended in the water for a very long time.

[0007] In order to overcome these different problems, we will not use the venturi effect as the sole method of air injection, and we sequence the process in three stages: a strictly hydraulic turbine, an air injection system and an anti-cavitation system.

[0008] The chosen method consists of generating a conical turbulence that flares downwards, and introducing into the upper part of this cone the precise quantity of air required to oxygenate the water in the form of calibrated bubbles that strictly exclude the most small and finally to install at the top of the turbine an anti-cavitation system necessary to isolate the machine from the surface.

[0009] The oxygenation of the water, in the case where the machine is installed alone, takes place in several stages: the injected air begins by descending into the turbulence cone, with the widening of the cone, the flow of water and mixed bubbles gradually slows down.

[0010] When the rising speed of the bubbles (which is a function of their diameter) allows it, these bubbles enter the turbulence and are ejected laterally: the depth at which this occurs can be chosen by varying either the size of the bubbles, or the ejection speed of the water by the hydraulic turbine and its deceleration speed (a function of the angle of the generated cone).

[0011] The bubbles then rise, passing through the lateral current feeding the turbine. [Fig.1].

[0012] It is therefore the widening of this cone that moves the bubbles away from the turbine.

[0013] And it is their homogeneous and rapid ascent that prevents them from returning to the turbine.

[0014] The water entering the system is therefore first oxygenated by the rising bubbles, then to a small extent during transit through the cone of turbulence, the main oxygenation occurring when the bubbles pass through the turbulence, the weight of the water column present at this level inducing super-saturation.

[0015] The energy used serves a little to bring the required quantity of air to the desired depth, but above all to moderately accelerate a large volume of water.

[0016] Description of the three elements constituting the machine:

[0017] 1) The Hydraulic Turbine

[0018] It is implanted on the surface, with the upper part emerging. See [Fig. 1] and 2.

[0019] The hydraulic turbine must sufficiently accelerate the water forming the descending cone in order to obtain a sort of bell shape that flares out at the bottom, impenetrable by air bubbles.

[0020] If the water then flows through a reinjection tube (see the previously cited pending patent), the desired velocity in this tube determines the initial velocity (VO) and the accelerated volume. If the machine is installed alone, the depth chosen for the bubble exit determines the initial velocity. The two parameters for the initial velocity at which the water exits the turbine are the propeller pitch and its rotational speed. The deceleration depends on the cone opening angle: in open water, with air injection, this angle is approximately 30°, but the presence of the basin bottom induces both lateral ejection of the moving water and overpressure at the bottom of the cone, leading to its flare. A 60° angle is thus observed under the installation's limiting conditions. of the machine described as an example, with 400 watts of motor power and 550mm of basin depth. [Fig.4].

[0021] The calculations are performed on a cone with a 40° average opening, using the tangent of the semi-cone angle (i.e., 20°), the apex of which is the tip of a blade. By using simplified blades cut from a flat sheet, the speed at the blade tip must be limited. Above 10 meters per second, it is necessary to use complex blades (with a progressive profile to ensure a constant pitch): At 1410 rpm, this limits the turbine diameter to 130 mm, or a radius of 65 mm with 45 mm blades (the shaft being 40 mm in diameter). Note that increasing the number of installed blades increases the thrust obtained.

[0022] The turbine design must be based on the desired cone. The tangent for an angle of 20° is 0.364. The calculation is therefore: 0.364 x h (cone height) = r. To obtain the radius of the disk described by the cone in the plane perpendicular to the depth h, the turbine radius must be added, giving rl. The depth h is the one chosen based on the installation (such as the basin depth) for the bubble outlet. Next, the velocity VI (bubble ascent velocity) is determined, and then the required water volume is calculated: VI x 3.141 x rl x rl, this same volume being delivered by the turbine.

[0023] In the example of the 400 w machine, installed in a basin 1 meter deep, the turbine is at a depth of approximately 0.185 meters (the blades are 15mm above) and the bubbles delivered are 6mm in diameter (therefore Vl=0.20 meters per second)

[0024] We have: 0.364 x 63 = 22.9 = r. And rl = r + 6.5 = 29.4 cm. The disk therefore has a surface area of: 3.141 x 29.4 x 29.4 = 2715 cm². To have a flow rate of 0.2 m / s, this requires 54.31 liters per second. With a propeller pitch of 19.5 cm and a rotational speed of 1410 rpm, we have V₀ = 4.52, the turbine diameter being 130 mm as we have seen.

[0025] The length and surface area of ​​the blades determine the power absorbed, as they influence the volume of water set in motion. This allows for adjusting the exact power absorbed by the electric motor. It is 400 watts (+ / -10%) in the example shown in the figures.

[0026] A large diameter shaft must be used firstly because the air injector described later is inserted into it, secondly because by removing the central part of the propeller we have a more homogeneous pitch of the blades and finally to reduce the shear zone naturally present downstream due to the thickness of the blades (the longer they are, the thicker they must be).

[0027] This axis is a smooth tube of constant diameter, in order to avoid any convergence amplifying the downstream shear zone. The surface of the disk described by its diameter in square centimeters is 1 / 30 of the installed power in w / h — or close if standard tubes are used.

[0028] Finally, the blades are positioned far enough from the lower edge of the turbine to allow the turbulence immediately downstream of them to dissipate before the air is introduced. A distance of fifteen times the thickness of the sheet metal used to manufacture them is maintained between the base of the blades and the air injectors.

[0029] A minimum of 3 blades is required to obtain a consistent thrust. In practice, there are 3 turbulent currents (one for each blade) following concentric spiral trajectories that form the cone designed to contain the bubbles. When the bubbles manage to enter these turbulent currents forming the cone, specifically the gaps separating these spirals, they abruptly slow the water flow, causing a rapid ejection of the bubbles trapped in the cone, and these bubbles then begin to rise (VI).

[0030] The desired turbine flow rate is 350 to 500 litres of water stirred per watt absorbed (per hour).

[0031] The water ejection speed by the turbine must be 4 to 5 meters per second.

[0032] With the same motive power, one can either accelerate a lot of water moderately, as in a shallow basin, or accelerate less water more strongly, for example to send the water / bubbles flow deeper.

[0033] At the top, above the surface, the turbine shaft fits onto a spacer welded to the drive shaft. This shaft receives the motive power via a surface coupling, the motor being "out of the water" [Fig. 2]. At the bottom of the drive shaft, a standard thread receives the bolt / washer assembly which secures the air injection system. [Fig. 3].

[0034] The assembly rotates; to prevent any risk of the machine coming apart, the assemblies are glued.

[0035] The cone formed by the water ejected from below corresponds to another inverted cone corresponding to the water inlet. The whole assembly forms a kind of diabolo, the narrow end of which is occupied by the drive blades. Only the water passing through this point (in red [Fig. 1]) can cause cavitation; the air responsible for this could either rise in turbulence generated by the blades, but this is excluded because the thin blades are located well upstream of the air injector.

[0036] This air can also come from above: either it enters along the axis of the turbine, which will be excluded by the anti-cavitation plate described later, or it arrives in the form of small bubbles transported by the water - hence the need to use a specific air injection system.

[0037] As it stands, this turbine is unsuitable for the insertion of air and is subject to strong cavitation because it is located close to the surface - the water only arrives laterally.

[0038] 2) The Air Injection System:

[0039] It is necessary to use a complementary system, because both the shear and the depression, naturally present downstream of this type of installation, have been deliberately attenuated.

[0040] In addition to centering and locking the hydraulic turbine on the drive shaft, this system must perform three operations:

[0041] - Eject from the system the water that enters it when the system is stopped and which is therefore present at startup.

[0042] - Allow the introduction of the required quantity (for oxygenation) of air into the conical turbulence generated by the hydraulic turbine.

[0043] - Introduce air in the form of bubbles of the chosen and homogeneous size. All inclusion of small bubbles that could be brought back into contact with the turbine is excluded; similarly, bubbles that are too large are likely to fragment and therefore generate smaller ones.

[0044] The chosen method relies on a centrifugal effect caused by the trajectory of the pipes supplying the air:

[0045] By using tubes to deliver the air, this effect can be achieved by having them adopt a re-entrant curve; the air outlets are located at the periphery, then the tubes are quickly brought back against the drive shaft where they are fixed before rising against this shaft to the surface. At start-up, this causes the almost instantaneous expulsion of the water present in the pipes due to the high density of water. [Fig. 3].

[0046] Once this water has left, the centrifugal force combines with the low pressure naturally present under the large-diameter axis to deliver a stream of bubbles. There is also a Venturi effect due to the rapid movement of the nozzles in the water; to mitigate this, a relatively slow-rotating motor is used, specifically 1410 rpm in the example given. In practice, experimentation has shown that the air ejection velocity, under the described installation conditions, is approximately two-thirds of the nozzle movement velocity due to their rotation.

[0047] The diameter and number of air supply ducts determine the quantity of air actually delivered. This quantity is determined by the amount of oxygen to be fixed multiplied by the fixation coefficient: In the machine covered by patent N FR106072, this quantity is 5 to 7 grams per watt absorbed with a coefficient greater than 75 percent. When the machine is used alone, it is expected to fix up to 3 grams per watt with 50 percent fixation, which is therefore roughly the same in terms of the volume of air required. In the 400-watt machine described, this requires the injection of 10 cubic meters of air.

[0048] per hour (i.e. more than 2000 grams of oxygen), i.e. half the volume of currently distributed side-ejection turbines.

[0049] The maximum air flow rate required is therefore approximately 25 liters per watt of motorization.

[0050] The diameter of these pipes determines the diameter of the released bubbles and the rotational speed, and therefore the movement speed, of the nozzles that form the initially elongated bubbles. This results in a string of bubbles with a uniform diameter, slightly larger than that of the injection tubes supplying the air. According to the literature, the shape and ascent speed are consistent between 2 and 10 millimeters in diameter; therefore, 4.6-millimeter tubes were chosen, releasing a string of homogeneous bubbles 5 to 6 millimeters in diameter with an ascent speed of 20 centimeters per second in water, for the 400-watt machine. At this speed, the bubbles rise too quickly to be drawn back into the turbine by passing through the incoming current. They exit the cone approximately 80 centimeters below the surface, either when the current has slowed sufficiently, or at the speed (VI) already mentioned. These bubbles therefore remain underwater for several seconds.

[0051] The quantity of air (with 20% oxygen) required to oxygenate the water (in mg / L, i.e., parts per million) is very small; therefore, this system consumes little energy, but is very sensitive to the environment: immersion depth or unwanted turbulence. The immersion depth must be constant, and it is not advisable to enclose the turbine; the introduction of any foreign body or risk of fouling must also be avoided.

[0052] The immersion depth can be used to adjust the air flow: in the 400 watt machine it is 190 millimeters + / -5 mm (for 10 cubic meters of air and 8 injection tubes), but by varying it by plus or minus 20 millimeters the air flow varies by plus or minus 25 percent.

[0053] In practice, the air injection system consists of a metal disc that fits precisely into the base of the turbine. This disc is drilled in its center so that it can be bolted to the drive shaft, which centers and secures the turbine to the drive shaft.

[0054] On the periphery of this disc, as many reserves are drilled as there are planned air supply tubes, taking care to distribute them regularly.

[0055] These tubes are welded or glued at the level of these reservoirs, then brought back against the drive shaft where they are fixed; they then travel through the turbine in order to protrude above the level of the water surface.

[0056] During assembly, the various elements are coated with silicone to prevent any unwanted leakage.

[0057] 3) Anti-Cavitation System:

[0058] It is the vertical surface mounting that makes it indispensable, firstly because the water arrives only laterally, creating a vortex along the turbine axis that could introduce air, and secondly because bubbles circulating below the surface—especially if a film of dust or grease is present, for example, following the distribution of food—could be drawn into the system. However, as previously discussed ([Fig. 1]), only surface water feeds the central part of the "diabolo" and must therefore be free of any bubbles.

[0059] The associated water blade must therefore circulate outside the volume delimited by a 60° opening cone having as its apex the center of the injection disc and as its base the anti-cavitation plate, which determines the minimum dimensions of this plate.

[0060] A rectangular shape is preferred in order to limit the acceleration of the incoming current which in practice rotates in the same direction as the turbine, each angle generating turbulence.

[0061] A simple plate or sheet of metal is used to absorb the pressure drop along the turbine shaft. This plate is pierced in its center to allow the turbine to pass through it. A gap is deliberately left to avoid any friction. Two opposing notches allow the spacer to pass through, which also serves to secure the turbine in the event of a possible disconnection, as the turbine remains suspended from the plate instead of falling.

[0062] Its minimum surface being that of the vortex likely to form in its absence (although it is advantageous to provide it to be larger), it results from this surface a sufficient slowing of the flow supplying the machine (the upper cone forming the "diabolo" is very flattened due to the surface location) so that any bubbles brought back towards the turbine cannot fall back under the anti-cavitation plate.

[0063] It must be slightly immersed (approximately 30 mm), firstly so that water can circulate above it to fill the depression induced at the level of the gap left between the anti-cavitation plate and the turbine shaft, secondly to trap between this plate and the surface or the base of the float, any bubbles circulating below the surface or against the base of the float.

[0064] This plate is fixed to the structure supporting the motor [Fig.2] and [Fig.4].

[0065] Implementation and Performance:

[0066] This turbine can be installed on the machine which is the subject of our patent FR106072.

[0067] Its air and water flow rates are compatible with those of this machine, and the turbine immersion depth is compatible with that required. A simple metal frame fixed to the structure allows the motor to be fixed at the top, and the anti-cavitation plate below as shown in [Fig.2].

[0068] It can also be used alone in shallow basins, from a few tens of centimeters to two or three meters deep; beyond that, a reinjection tube, as in the previously cited patent, must be used to stop the deceleration of the flow. It is installed on a stable float, equipped with two opposing mooring lines, otherwise the installation will rotate on its own axis. [Fig. 4]

[0069] Since the turbine generates an upward counter-thrust, the installation must have a minimum weight (approximately 60 kilograms per horsepower used). The resulting immersion helps to deflect foam and stabilizes the assembly. The central well must have a rim on its lower part to prevent any recycling of bubbles present against the submerged face of the float. As the air introduced into the machine passes through this well, it is possible to install a vent and a damper to close the air inlet. Under certain conditions, namely large machines with significant reinjection tubes, it may be necessary to start the installation without air, thus priming the system before introducing air only once sufficient kinetic energy has been accumulated. The same result is obtained with a gradual start-up of the machine.

[0070] The anti-cavitation plate is fixed 3 centimeters below the float.

[0071] An anti-intrusion protection consisting of a frame supporting a suitable mesh is essential; this protection must not interfere with the turbulence cone, only the lower face being traversed by the ejected flow. See [Fig.4].

[0072] Installing this machine in a body of water results in the formation of a cloud of air bubbles below. A vast – several meters – turbulence is established: the water arrives laterally at the surface, is then accelerated and mixed with the air bubbles. [Fig. 1].

[0073] The water then flows against the bottom of the basin before returning to the turbine.

[0074] Oxygen is no longer the limiting element, it is injected in abundance.

[0075] A potential yield of two to three grams per watt absorbed is conceivable:

[0076] - Water is not raised, it is only stirred, which is the main source of energy saving.

[0077] - The bubbles remain in the water for several seconds, which promotes exchanges gaseous.

[0078] - By oxygenating the basin from the bottom, a relative supersaturation is achieved:

[0079] In a typical rainbow trout rearing pond, the water (at approximately 14 / 15°C) contains 10 mg / liter of oxygen at the inlet. If the aerator is placed in the pond when this level has dropped to 5 mg / liter, 5 grams of oxygen can be fixed per cubic meter treated. However, since our machine sends the bubbles to the bottom—usually 1 meter deep—the oxygen level can rise to 11 mg / liter due to the pressure of the water column, and the fish will be able to extract 6 mg / liter instead of 5, i.e., 20% more.

[0080] - By stirring up a lot of water, more than double what is raised by the machines Currently, the main factor determining the actual output is the amount of oxygen consumed in the machine, which depends on the number of fish placed in the turbulence generated by the machine. Conversely, a conventional aerator (1 HP) that lifts 100 tons of water per hour will not be able to fix more than 500 grams of oxygen per hour under the conditions described above.

[0081] Three other significant advantages can be added:

[0082] - Our machine is usable in all seasons, including in freezing weather.

[0083] - Only the purring of the engine is audible, instead of the sound of cataracts produced by current machines.

[0084] - Fish congregate around existing aerators, "sucking" oxygen by On the surface, the fish show no interest whatsoever: after a few minutes of operation, they colonize the current along the bottom of the tank and then gradually spread throughout the entire available volume. There is no longer any perceptible stress, aggression, or contact between them, which reduces the risk of disease and improves feed conversion.

[0085] Areas of application:

[0086] This machine was developed to equip the one described in our patent No. FR2000351.

[0087] The various tests carried out in fish farms have demonstrated an efficiency unrelated to current equipment. This can be described as a technological breakthrough.

[0088] In larger formats, this machine can replace the aerators used in purification systems, but also at the level of discharges into the natural environment — particularly urban — because it is very quiet.

[0089] A 250 watt machine would be suitable for shellfish ponds or small fish ponds.

[0090] Equipped with a tube channeling the water to the desired depth, this aerator is particularly suitable for breeding in suspended cages.

[0091] Finally, it can be installed in all environments subject to eutrophication or asphyxiation problems, provided that they are of a compatible depth. Brief description of the drawings

[0092] -1): Description of the general operating principle.

[0093] -2): Example of a load-bearing chassis.

[0094] -3): Drawing of a typical 400-watt turbine. VO = 4.52 meters per second at 1410 rpm / min.

[0095] -4): Plan of a typical autonomous installation.

[0096] - Power 400 watts, IP55 motor rotating at 1410 rpm.

[0097] - Float of 600 mm by 600 mm, thickness 250 mm.

[0098] - Eight air supply tubes with a diameter of 4.6 mm, injecting approximately 10 meters air cubes per hour.

[0099] - Total weight 30 kilograms: Engine 7 kg, float with concrete insert 19 kg and protective grille and miscellaneous items 4 kg.

[0100] - VO=4.52 m / s and Vl=0.2 m / s. Bubble exit depth: between 800 and 1000 mm. Flow rate: More than 195 cubic meters per hour; the total volume set in motion being significantly greater (see blue arrows [Fig.1]).

[0101] Figure Captions:

[0102] [Fig. 1] “Description of the process”

[0103] - Turbine installed vertically on the surface with anti-cavitation plate.

[0104] - Turbulence generated by the machine, in red the incoming flow free of bubbles, In green, the outgoing flow forming the cone at approximately 40°. In blue, the vast eddy with the trajectory of the air bubbles.

[0105] - Turbine outlet speed (V0).

[0106] - Bubble exit / rebound velocity (VI).

[0107] [Fig.2] “Example of support for installation patent no. 102072”

[0108] a): electric motor.

[0109] b): support made of welded tubes.

[0110] c): anti-cavitation plate. [YES] d): turbine.

[0112] [Fig.3] “Elements constituting the turbine”

[0113] a): motor shaft (metal tube whose inner diameter is equal to the diameter of the shaft of the motor used).

[0114] b): spacer with anti-water-backflow washer.

[0115] c): low thread.

[0116] d): turbine (large diameter smooth tube).

[0117] e): sheet metal blades.

[0118] f): injection disc.

[0119] g): injection tubes.

[0120] h): bolt / washer assembling everything.

[0121] [Fig.4] “Typical installation for salmon farming”. Ejection of bubbles at approximately 800 mm below the surface.

[0122] 400 watt motor, 1410 rpm, IP 55. (7.5 kg).

[0123] Float, 19 kg, 600x600 mm. Thickness, 250 mm. Central well diameter of 125 mm. 2 cm concrete insert. Molded HDPE or Polystyrene or aluminum sheet.

[0124] V0= 4.52 (meters per second) and V1= 0.2 (meters per second).

[0125] a): motor.

[0126] b): float.

[0127] c) :2 threaded rods of 10 mm diameter (structure the assembly).

[0128] d): Stainless steel 316 turbine: Overall length 405 mm, turbine shaft tube 305 mm 40 mm long and 40 mm in diameter. Shaft made of 14 mm inner diameter tubing, 400 mm long. Turbine diameter 130 mm, air injection disc, blades and spacer made of 1 mm sheet metal. Air supply tubes made of 4.6 mm inner diameter HDPE. Turbine pitch is 195 mm.

[0129] e): anti-cavitation plate (30 mm below float, 95 mm below surface), approximately 500x400x3mm. 3 mm aluminum sheet.

[0130] f): metal frame supporting the protective grille (3.5 kg), 500 mm minimum diameter and 500 mm long.

Claims

1.

2. Demands A vertical turbine surface aerator that generates a cloud of air bubbles beneath the machine without cavitation, unlike current aerators which are either upward-moving or side-discharge. This is achieved by generating a specific conical turbulence with an opening of 30 to 40 degrees, which, while drawing the required quantity of air bubbles to a precise depth, keeps them sufficiently away from the hydraulic blades. This aerator is composed of three distinct elements that sequence the process: a strictly hydraulic turbine generating a conical turbulence of approximately thirty to forty degrees of opening; an air injection system based on a centrifugal effect that delivers the precise quantity of air in the form of calibrated bubbles at the apex of the aforementioned cone; and finally, an anti-cavitation system that isolates the propeller from the surface and traps bubbles that could cause cavitation.The integration of these three elements eliminates cavitation, with significantly higher efficiency due to the absence of water elevation and gas exchange being enhanced by the extended transit time of air bubbles in the water. A vertical downward turbine surface aerator according to the preceding claim, characterized in that the hydraulic turbine is organized around a vertically mounted axis, the upper end of which protrudes above the surface, the air introduced into the system passing through it, this axis being a smooth tube of constant diameter, in order to avoid any diverging or converging flow as well as any parasitic turbulence, the diameter of this axis being proportional to the power in watts per hour implemented, its calculation being: Surface area of ​​the disk delimited by its diameter in square centimeters equal to one-thirtieth of the power in watts per hour implemented or close to this value if standard tubes are used in order to optimize the design of the drive blades,The turbine has at least three blades positioned fifteen times the thickness of the sheet metal from which they are made above the air injectors to prevent any air from rising and degrading the turbine's performance, while maintaining a homogeneous thrust, with the rotational speed measured at the blade tip being less than or equal to 10 meters per second to allow,

3.

4. the use of simplified blades, cut from a flat sheet, while generating a thrust compatible with the desired turbulence, the pitch of the blades must allow the ejection of 350 to 500 liters per hour and per watt of motorization at a vertical speed of 5 to 4 meters per second to generate the specific conical turbulence, the number and surface area of ​​the blades installed allowing the performance to be adapted, the diameter being limited, in order to drive the bubbles to the chosen depth, while stirring the maximum amount of water. A surface aerator with a downward vertical turbine according to any one of the preceding claims, characterized in that the air injection system is based on a specific device combining three forces at the upper level of the cone, driving the air bubbles towards the bottom, and is organized around a disc obstructing the base of the hydraulic turbine shaft, which it centers and secures to the drive shaft. This disc is pierced in its center to receive the bolt locking it onto the drive shaft. Reservations, to which the air supply tubes are attached, are regularly arranged around the periphery of this disc. These tubes rise to the surface, passing between the drive shaft and the tube forming the turbine shaft, such that they follow a re-entrant curve in the lower part, being quickly brought back against the drive shaft to which they are attached.In order to generate a centrifugal effect essential for purging the system and then ejecting a volume of air compatible with the desired oxygen volume, the diameter of the generated bubbles is determined by the chosen diameter of these tubes while ensuring their homogeneity. This diameter determines, on the one hand, the depth at which they begin to rise, but also their propensity to be brought back by the current in contact with the turbine. The number, added to the diameter, of these tubes allows the potential air flow rate of the machine to be sized. The installation immediately downstream of the hydraulic turbine axis allows the relative depression that exists at this point to be taken advantage of. The string of bubbles is generated by the movement in the water resulting from the rotation, in addition to the two previous effects. A vertical downward turbine surface aerator according to any one of the preceding claims, characterized in that the anti-cavitation system is located in the upper part of the turbine so as to absorb the pressure drop that forms around the axis because the water air only enters laterally due to the surface mounting. To prevent any air intrusion, the system is cut from a sufficiently resistant plate or sheet and pierced in its center to avoid contact with the turbine passing through it. Its minimum surface area is that of the vortex likely to form, namely that of the base of a 60° cone with its apex at the center of the air injector disc. This base must be submerged a few centimeters. The plate is slightly submerged at a constant depth, hence the need to fix it to the installation support to trap any air bubbles returning towards the turbine while filling the depression naturally present at the level of the hole allowing the turbine to pass through. Preferably, the shape of the hole is angular to counteract the rotation of the incoming flow, and the surface area is sufficient to prevent any risk of bubbles intruding under the plate.This surface area must be adapted according to the environment.

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