A kind of direct-cooling type icing wind tunnel implementation method and system
Technical field
The invention belongs to aerodynamics experimental technique field, relate to implementation method and the system of icing wind tunnel.
Background technology
It is the main weather factor that causes aircraft accident that aircraft freezes, so all aircraft is frozen as important air worthiness regulation in various countries' flight air worthiness regulations (comprising China CCAR25 section and U.S. FAR25 section).From the scientific research angle, it is crystallization process under the strong convection environment that aircraft freezes, it is the point of crossing of aircraft aerodynamics and condensed state physics, therefore widely research has all been carried out to mechanism and impact that aircraft freezes in countries in the world, and wherein utilizing icing wind tunnel is research means and the seaworthiness checking means that extensively adopt in ground research aircraft ice formation issues.
Wind-tunnel is the main flow equipment of aerodynamics ground equipment, and its purpose of design is exactly to produce the quality that the required air-flow of test is used for measuring flow field around the object in a pipeline, and the key parameters such as the suffered aerodynamic force of these objects and Aerodynamic Heating.Icing wind tunnel is for measuring object when air freezes, the form of ice and the wind-tunnel of flow field change.Two types of wind-tunnel are arranged:
(1) return circuit wind tunnel:
As shown in Figure 1, the maximum characteristics of return circuit wind tunnel are that the wind tunnel body is a circulating line, and the test air-flow can circulate in pipeline.The advantage of return circuit wind tunnel is the air-flow with kinetic energy can be reused, thereby reach the purpose that reduces the wind tunnel operation energy, shortcoming is to need to increase fairing with the mobile quality of warranty test section air-flow, so its construction cost is higher, the structure relative complex, but operating cost is low.
(2) direct-action wind tunnel:
As shown in Figure 2, the maximum characteristics of direct-action wind tunnel are that the wind tunnel body is a straight pipeline, and the test air-flow flows into from an end, flows out from the other end.The advantage of direct-action wind tunnel is simple in structure, and construction cost is low, and shortcoming is that consumes energy is larger, and operating cost is higher.
Icing wind tunnel is mainly used in simulated aircraft freezing process in the clouds, is the main tool that research aircraft freezes.For reaching this purpose, need in wind-tunnel, prepare and environment like the cloud layer environmental facies, comprise the water smoke environment with fine drop, lower gas flow temperature, speed and the model surface temperature of low-temperature airflow.
The icing wind tunnel that the world builds up at present in usefulness has more than 30, in these wind-tunnel, in order to reach the purpose of the icing environment of simulation, all installed air-flow cooling system and spraying system-cooling system additional for reducing gas flow temperature, spraying system is used for the water vapour environment of simulation cloud layer.The cooling system that installs additional at present consists of by compressor and heat exchanger two large divisions.Gas flow temperature obtains with the mode of air-conditioning cooling, and the water smoke environment forms with a large amount of atomizer ejection water smokes.In this manner, ooling channel need to be laid on wind-tunnel inside, when test air flow stream supercooling agent pipeline, by and tube wall between heat exchange finish cooling procedure.Because ooling channel has perturbation action to air-flow, therefore need to increase the devices such as damping screen of steady air flow, the loss that further strengthens airflow kinetic energy.For this reason, conventional junction icing tunnel complex structure, energy consumption is very large, and construction cost and operating cost are all very high.
Take the icing wind tunnel at U.S. Glenn center as example, this wind-tunnel is return circuit wind tunnel, its test section is of a size of 2.74m x1.83mx 6.1m, refrigeration system adopts cold-producing medium (freon) refrigeration, the very large heat exchanger of resistance not only to be set in wind-tunnel inside in order to cool off air themperature in the wind-tunnel, need simultaneously a large-scale refrigeration plant to provide required cold for refrigeration system, its heat exchanger is made of two plate heat exchanger of 850 tons of weighing, and spraying system then is comprised of the spraying rake that 1000 small nozzles consist of.These equipment all are placed in the wind-tunnel, have greatly increased resistance to flow, thereby need very high blower fan driving power, make the icing wind tunnel test become the very high pilot project of power consumption, the construction of icing wind tunnel and operating cost thereby also very high.
Summary of the invention
The object of the invention is to propose a kind of new icing wind tunnel method for designing by changing the type of cooling of test gas, simplifies the icing wind tunnel structure to reach, improves efficiency of energy utilization, and then reach the purpose that reduces icing wind tunnel construction and operating cost.
The object of the present invention is achieved like this:
Upstream at test chamber evenly sprays into cryogenic gas, reduces the temperature of testing air-flow by the direct hybrid mode of gas-gas, makes it to reach the required temperature of icing tests.When temperature is reduced to dew point when following, contained moisture will be separated out because of condensation and be become small drop in the air.Because gas-air mixer mode heat exchange efficiency is higher than the wall pipe type heat transfer that adopts in the conventional junction icing tunnel, simultaneously gas-air mixer heat exchange need not adopted cooling Pipe bundle structure, so the structure of refrigeration system will simplify greatly, and resistance to flow also will reduce greatly.
In order to control the model surface temperature, test model can be designed to the version with hollow cavity.In process of the test, low temperature nitrogen will be injected into hollow cavity to reduce and control model surface temperature.For the relative humidity of warranty test air-flow is enough, size droplet diameter meets in water smoke and the cloud layer for reality produces simultaneously, can increase the assisted atomization device in wind-tunnel.
As shown in the above description, the present invention is by adopting the new heat exchange type of cooling, to reduce the test temperature water smoke required with preparing icing tests by condensation combines, simplified the icing wind tunnel structure, reduce disturbance and the loss of the icing system of low temperature to air-flow in the wind-tunnel, can reduce undoubtedly construction and the operating cost of icing wind tunnel.
In order to reduce to greatest extent refrigerating gas to the disturbance of test air-flow, preferably use the low temperature nitrogen that is similar to the air molecule amount as refrigerant gas.Low temperature nitrogen is obtained by liquid nitrogen gasification, because liquid nitrogen temperature approaches-196 ℃, therefore can reach with less flow the purpose to the air fast-refrigerating.If again sprinkling equipment and the construction of wind tunnel of low temperature nitrogen are done integrated design, import from blower fan static blade or center fiaring cone such as the pipeline with low temperature nitrogen, then can further reduce the perturbation action to air-flow.
The present invention is a kind of new method of icing wind tunnel design.Cryogenic gas is added moist test air-flow, and the mode by direct cooling reduces the test gas flow temperature, and the condensate moisture in the air-flow is become drop, forms the required low temperature water smoke environment of icing tests.As supplementary means, can set up humidity and size droplet diameter distribution that the assisted atomization system is used for the adjusting test air-flow.
In process of the test, the span by adjusting test gas flow temperature, size droplet diameter distribution and test model surface temperature can form different icing tests parameter combinations, thereby obtain different ice types at model in test chamber.Because the nitrogen stable chemical nature, molecular weight is near the air molecule amount, and the market price is not high simultaneously, therefore is specially adapted in this test the cooling to humid air.
Compare with employing tube wall type cooling in the existing icing wind tunnel design, the direct cooling mode that the present invention proposes has higher heat exchange efficiency, the simultaneity factor structural design also is simplified, can greatly reduce the energy consumption of icing wind tunnel and build operating cost, both can be used for direct-action wind tunnel, also can be used for return circuit wind tunnel.Because it is less to increase the required structural modification amount of this cover system, also can be used for transforming existing conventional wind-tunnel as icing wind tunnel.
Description of drawings
Fig. 1 is the return circuit wind tunnel synoptic diagram.
Fig. 2 is air suction type direct current wind-tunnel synoptic diagram.
Fig. 3 is direct-cooling type icing wind tunnel schematic diagram of the present invention.
11. blower fans, 12. cryogenic gas entrances, 13. cryogenic gas spray apertures, 14. contraction sections, 15. test models, 16. test chambers among the figure
Fig. 4 is the synoptic diagram of direct-cooling type icing wind tunnel subsystem.
21. low temperature sources of the gas, 22. cryogenic gas spray systems, 23. model cooling systems, 24. assisted atomization systems, 25. fan blades, 26. wind-tunnel, 27. cryogenic gases export 28. gas pipe lines among the figure
Fig. 5 is cryogenic gas spray system and blower fan integrated design synoptic diagram.
31. wind tunnel bodies, 32. cryogenic gas entrances, 33. cryogenic gas spray apertures among the figure
Embodiment
The present invention is the new method of a kind of icing wind tunnel design, is characterized in directly cooling off test air-flow in the wind-tunnel with cryogenic gas, and the condensate moisture in the test gas of humidity is become drop, obtains the required low temperature water smoke environment of icing tests.Cryogenic gas can simultaneously for reducing the test model surface temperature, to obtain different parameter combinations between test gas temperature, size droplet diameter distribution and the model surface temperature, obtain different ice types at model.
Further, a small-sized assistant spray system 24 be can set up in the test and the humidity of test gas and the size droplet diameter distribution of water smoke are used for changing.
Comprise cryogenic gas spray system 22, model cooling system 23,24 3 major parts of assistant spray system in the icing wind tunnel design according to the present invention's proposition, wherein cryogenic gas spray system 22 is installed in the upstream of test chamber 16, is used for cryogenic gas is sprayed into the test air-flow; Model cooling system 23 is used for the cooling test model, in order to obtain lower surface temperature; Assistant spray system 24 is installed in the upstream of test section, and the particle diameter that is used for adjusting test water smoke drop distributes and moisture content.
In above-mentioned three sub-systems, cryogenic gas spray system 22 is made of low temperature source of the gas 21, gas pipe line 28 and spray equipment 27.The cryogenic gas flow can be controlled with valve, and inputs with flowmeter, thermometer monitoring cold.Cryogenic gas nozzle 22 is used for cryogenic gas is sprayed into the test air-flow, its basic structure is identical with the conventional gas nozzle, to note in the actual design being complementary with the test gas velocity, in order to avoid air-flow is caused excessive disturbance, such as can the cryogenic gas piping laying is inner at static blade or the center fiaring cone of blower fan.
The model cooling system consists of by low temperature source of the gas 21, gas pipe line 28 with the test model 15 of hollow gas chamber.The low temperature source of the gas here can share a source of the gas with the cryogenic gas spray system, also can use independently source of the gas.Because the cold that the model cooling needs is lower, low temperature model cooling system also can adopt other type of cooling to cool off.When the mode that adopts cryogenic gas directly to cool off, the hollow gas chamber in the model need to design according to the structure of model, to guarantee that model surface can access effective cooling.Hollow gas chamber has the entrance and exit of cryogenic gas, in order to replenish later on new cryogenic gas in cold consumption.
Assistant spray system 24 is autonomous system, is made of water pump and atomizer.Water pump pushes atomizer with water and background pressure is provided, and sprays into the test air-flow after then by atomizer aqueous water being atomized, and freezes at model at last, and unnecessary water is then discharged wind-tunnel by discharge pipe line.
The present invention adopts the mode of cryogenic gas cooling test air-flow, and airborne condensate moisture is become small droplet, and reaches simultaneously the purpose that reduces the test gas flow temperature.
Adopt cryogenic gas adjusting test model surface temperature, reach the purpose of control ice-formation condition.
Cryogenic gas spray system 22 and blower fan 11 static blades or center fiaring cone are done integrated design, to reach the purpose that reduces gas-flow resistance.
Adopt the assistant spray system to regulate size droplet diameter distribution and content in the water smoke, thereby obtain the required test condition that freezes.
Embodiment 1. small-sized DC formula icing wind tunnels
For small-sized DC formula wind-tunnel, suppose that the test chamber size is 0.15x0.15x0.30m, the wind-tunnel speed of incoming flow is 8m/s, flow is 0.18m
3/ s, temperature is 5 ℃, tests required gas flow temperature and is-5 ℃.In this example, cryogenic gas adopts low temperature nitrogen.Low temperature nitrogen is exported from liquid nitrogen container after the gasification because the loss of refrigeration capacity of pipeline, temperature is elevated to-193 ℃ by-196 ℃, suppose that simultaneously speed was identical with the test air-flow when low temperature nitrogen entered wind-tunnel from spray system, then the low temperature nitrogen flow of required importing is about 0.01m
3/ s only accounts for about 1/18 of test air-flow total amount.
Direct-action wind tunnel can be divided into again blowdown wind tunnel and two large classes of vacuum driven wind tunnel according to the difference of blower fan position.The assembling of blowdown wind tunnel is in the upstream of test section, and air-flow is blown into test section by blower fan and finishes test.The assembling of vacuum driven wind tunnel is in the downstream of test section, and air-flow flows into wind-tunnel from air inlet under the swabbing action of blower fan, blow out wind-tunnel from the other end again.
Direct-action wind tunnel among Fig. 3 is blowdown wind tunnel.When the design blowdown wind tunnel, usually motor is placed in the center cone.In order to reduce center cone to the disturbance of test air-flow, center cone is usually designed to a fairshaped cone.The latter half of hollow cone that is generally of cone.The implementation case transform hollow cone the spray equipment of cryogenic gas as, and the structure of spray equipment is similar to shower nozzle, comprises cavity and a plurality of spray orifice.Cryogenic gas is sprayed by spray orifice after injecting conical inner body again.Can control jet velocity and the flow of spray orifice by the pressure of regulating the low temperature source of the gas.The assisted atomization nozzle can be done integrated design with hollow cone, and we adopt single nozzle in this example, and nozzle is arranged on the center of center cone, so that the water smoke of ejection can be evenly distributed in the central area of air-flow.
Embodiment 2. small-sized reverse-flow type icing wind tunnels
The test section of supposing the direct-action wind tunnel in the described small-sized reverse-flow type icing wind tunnel of this example and the case 1 is measure-alike, is 0.15x0.15x0.30m, tests simultaneously gas velocity and equates that namely be similarly 8m/s, flow is 0.18m
3/ s, temperature is 5 ℃, test required gas flow temperature and be-5 ℃, then because the low-temperature airflow in the return circuit wind tunnel can be reused, that is to say that the cold that is injected in the test air-flow can be repeated to utilize, so after under the test air-flow reduces, the cold that at every turn fills into is the cold for losing owing to the equipment thermal loss only, so can estimate in return circuit wind tunnel, need the cryogenic gas flow of use less, namely less than 0.01m
3/ s.
On structural design, cryogenic gas spray equipment and assisted atomization system are arranged on the upstream of test section after integrated design.
Embodiment 3. large-scale reverse-flow type icing wind tunnels
Take the geometry of the U.S.'s large-scale icing wind tunnel in Glenn center and test parameters as reference, the hypothesis test section is of a size of 2.7x1.8x6m, and maximum wind velocity is 179m/s, and minimum temperature is-40 ℃, and can test under-25 ℃ of conditions the whole year.Indoor temperature is 10 ℃ during presumptive test, and the test wind is 100m/s, and test temperature is-25 ℃, and supposition has 2% cold leakage behind the test steady air current, and then flow of its test air-flow is 486m
3/ s.The cold that needs when starting is about 21000J/s, and the nitrogen flow that is used for cooling is 100m
3/ s, the nitrogen flow that needs after stablizing is 2m
3/ s.The wind-tunnel total length is about 70 meters, suppose to finish cooling procedure (cold air centers on wind-tunnel and runs a circle) when starting with 1 second time, need to consume 150 liters of liquid nitrogen when then starting, per second consumes 3 liters of liquid nitrogen of liquid nitrogen in the stable operation process, and 10 minutes words of test duration consume 1800 liters of liquid nitrogen of liquid nitrogen altogether.With 3 yuan of present liquid nitrogen market prices/rise calculating, then starting and finishing icing tests of 10 minutes needs to consume 1950 liters of liquid nitrogen altogether, is roughly equal to 5850 yuan of Renminbi.For so large-scale icing wind tunnel, this is quite to save.What need to remind is, has given enough surpluses in the above-mentioned calculating, and actual heat rejection should be less than 2%, and if icing tests carry out continuously, then as long as start and once just can carry out test of many times, expense also can reduce greatly.
The present invention revises the type of cooling in the design of conventional junction icing tunnel, changing the direct hybrid mode of gas-gas into cools off, thereby can greatly improve heat exchange efficiency, and simplify the icing wind tunnel design, be of practical significance for the efficiency of energy utilization that improves test, reduction experimentation cost.
The above-mentioned description to embodiment is can understand and apply the invention for ease of those skilled in the art.The person skilled in the art obviously can easily make various modifications to these embodiment, and needn't pass through performing creative labour being applied in the General Principle of this explanation among other embodiment.Therefore, the invention is not restricted to the embodiment here, those skilled in the art are according to announcement of the present invention, and not breaking away from the improvement that category of the present invention makes and revise all should be within protection scope of the present invention.