CN114813035B - Thermal surface cavitation synergistic resistance reduction test device and method - Google Patents
Thermal surface cavitation synergistic resistance reduction test device and method Download PDFInfo
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- CN114813035B CN114813035B CN202210379983.9A CN202210379983A CN114813035B CN 114813035 B CN114813035 B CN 114813035B CN 202210379983 A CN202210379983 A CN 202210379983A CN 114813035 B CN114813035 B CN 114813035B
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- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M10/00—Hydrodynamic testing; Arrangements in or on ship-testing tanks or water tunnels
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Abstract
The invention discloses a thermal surface cavitation synergistic resistance reduction test device and a method, relating to the field of hydromechanics, wherein the method comprises the following steps: the heater heats the metal body connected with the emitter; the emitter releases the metal body; adjusting the angle of the test bed to enable the metal body to enter water at different angles; the photographic device shoots the whole process image of the metal body after entering water; retrieving the metal bullet by the pick-and-place device; and calculating the drag reduction efficiency according to the obtained whole process image. Therefore, the invention provides a new idea for high-speed underwater design, and the technical basis is as follows: the metal body is heated to generate a bubble air film attached to the near wall surface of the metal body in underwater motion, so that the resistance is effectively reduced, no adverse effect is generated on the environment, specific test equipment and a method are provided for quantitatively testing the resistance reduction rate of the heated metal body entering water at different temperatures and angles, and the device has the advantages of simplicity in operation, high quantifiability, good repeatability and the like.
Description
Technical Field
The invention relates to the field of hydromechanics, in particular to a thermal surface cavitation synergistic drag reduction test device and a thermal surface cavitation synergistic drag reduction test method.
Background
The resistance of the object moving in the fluid is proportional to the density of the fluid, so that the resistance of the navigation body in the water is about 1000 times of the resistance of the aircraft in the air. Taking a ship as an example, the resistance of the ship in water mainly comprises differential pressure resistance, wave making resistance and frictional resistance, wherein the frictional resistance accounts for 50% -80% of the total resistance, so that the reduction of the frictional resistance has important practical significance in the aspects of increasing the speed of an underwater vehicle, increasing the voyage and the like.
The traditional micro-bubble drag reduction is also called air curtain and cavitation drag reduction, and is characterized in that bubbles are manufactured on the surface of an object to achieve the effects of drag reduction and noise reduction, namely air is released through air pipeline small holes paved around the surface of an aircraft to generate a large number of free micro-bubble air curtains which are dispersed finely. The basic principle is that the resistance is reduced by adjusting the bottom layer flow structure by utilizing the characteristics of small frictional resistance and easy deformation of the microbubbles, and the microbubble resistance reduction technology has the advantages of higher resistance reduction efficiency and longer persistence
In recent years, the resistance reduction performance of the actively injected microbubbles on the surface of an underwater navigation body is proved by the results of tests and numerical researches on flow resistance reduction. However, microbubbles generated by the conventional ventilation mode cannot stably reside, continuous ventilation is required, energy consumption is high, the microbubbles are easier to enter a high-flow-rate area, stable adhesion of the microbubbles on the wall surface cannot be realized, and the continuous drag reduction effect is poor. How to form stable bubbles in a near-wall area of a turbulent boundary layer is realized, and an air film is a key problem to be solved for improving the flow drag reduction performance. Therefore, in order to improve the range and the speed of the underwater vehicle, the invention of the active drag reduction test technology for forming the stable near-wall region air film by the thermal surface cavitation is urgently needed.
Disclosure of Invention
The invention provides a thermal surface cavitation synergistic drag reduction test device and a method, and aims to solve the problems in the prior art.
The invention adopts the following technical scheme:
a thermal surface cavitation synergistic resistance reduction test device comprises a water tank, a test bed, a heater, a transmitter, a metal body, a photographic device and a temperature measuring instrument, wherein the test bed is provided with at least one transmitter, the transmitter is detachably and vertically connected with the metal body, and the test bed is also provided with the heater for heating the metal body; the temperature measuring instrument is used for measuring the temperature of the metal body; the water tank is arranged below the emitter; the photographic device is arranged towards the water tank and used for recording the water inlet process of the metal body.
Further, the transmitter includes electro-magnet and pipe, the upper end fixed connection of pipe in the test bench, and be equipped with and be used for adsorbing the transmitter the electro-magnet.
Further, the heater is an electromagnetic heating coil and is wound on the conduit.
Further, the device also comprises a temperature measuring instrument for measuring the temperature of the metal body.
In a specific embodiment, the test bed further comprises a taking and placing device, the taking and placing device comprises a two-dimensional sliding table structure, a collecting disc and a lifting device, the test bed is provided with a bullet taking port and a bullet discharging port, and the bullet discharging port is provided with the guide pipe; the electromagnet can be arranged on the test bed in a reciprocating manner between the bullet taking port and the bullet placing port through the two-dimensional sliding table structure, the collecting disc is rotatably arranged on the inner bottom surface of the water cylinder, and at least two bullet grooves are annularly distributed at the upper end of the collecting disc; the lifting device is used for taking out the metal bullet from the bullet groove and lifting the metal bullet to the bullet taking opening.
In a specific embodiment, the test bed is arranged above the water cylinder in a swinging and adjusting mode through a swinging mechanism and used for changing the water inlet angle of the metal body; the swing mechanism comprises a connecting arm, a swing arm and a driving motor, the swing arms are arranged at the left end and the right end of the test bed, and the other end of each swing arm is pivoted with the connecting arm connected to the fixed surface; the two swing arms are connected with each other through a linkage shaft and are provided with the driving motor for rotating the linkage shaft; the taking and placing device further comprises a bucket body, the bucket body is arranged inside the water tank, the lower port of the bucket body is located above the elastic groove, the upper port of the bucket body is located below the emitter, and the upper port of the bucket body is provided with an inclined groove body matched with the swing mechanism and used for collecting the metal body.
A hot surface cavitation synergistic drag reduction test method adopts any one of the hot surface cavitation synergistic drag reduction test devices to carry out the following operations:
(1) Fixing a metal body at the bottom of the test bed through a transmitter;
(2) Heating the metal body to a preset temperature by a heater;
(3) Releasing the metal body by the emitter;
(4) Shooting the water entering process of the metal body through a photographic device, and acquiring an overall process image of the metal body after entering the water;
(5) According to the steps (1), (3) and (4), obtaining an image of the whole process of the unheated metal body at normal temperature after being put into water;
(6) And (5) calculating the drag reduction efficiency according to the whole process images obtained in the step (4) and the step (5).
Further comprising: and (4) respectively testing the metal bodies heated to different temperatures in the mode of the steps (1) to (4), and respectively calculating the respective drag reduction rates.
Further comprising: the metal warhead after entering water passes through the collecting disc through the taking and placing device, and is adsorbed on the electromagnet of the emitter again after the lifting device.
Further comprising: the angle of the test bed is changed through the swing mechanism, and the water inlet angle of the metal body is further changed.
Further, the calculation of the drag reduction efficiency is specifically:
processing and analyzing the whole process image in the step (5) to obtain the process time and the average speed of the unheated metal body after entering water and passing through a plurality of continuous metal body lengths, and calculating the corresponding acceleration a1; then, calculating the received resultant force F sigma 1 according to a formula F = ma;
processing and analyzing the whole process image in the step (4) to obtain the process time and the average speed of the heated metal body after the heated metal body enters water and passes through a plurality of continuous metal body lengths, and calculating the corresponding acceleration aT; then, calculating the received resultant force F sigma T according to the formula F = ma;
according to the formula η = (F) Σ1 -F ΣT )/F Σ1 And calculating the drag reduction rate eta.
Specifically, in the step (1), the emitter comprises an electromagnet and a guide pipe, and the metal body is fixed by electrifying the electromagnet; in the step (2), the heater is an electromagnetic heating coil wound on the conduit; in the step (3), the electromagnet is powered off to release the metal body, and the metal body falls down along the guide pipe; and (4) taking a high-speed camera as the photographic device to shoot to obtain an instantaneous high-definition image of the whole process of surface steam development after the metal body enters water.
In a specific embodiment, the metal body has a length of 45mm and a diameter of 9mm; the height of the lower end of the metal body from the water surface of the water tank is 0.78m when the metal body is connected with the emitter; the resolution of the high-speed camera is at least 2400 multiplied by 2400pi, and the frame number is at least 6400 frames/s.
From the above description of the structure of the present invention, it can be seen that the present invention has the following advantages:
the invention discloses a thermal surface cavitation synergistic resistance reduction test device and a thermal surface cavitation synergistic resistance reduction test method, which can be used for quantitatively testing the resistance reduction rate of a heated metal body entering water at different temperatures and/or different angles; the method has the advantages of simple operation, good quantifiability and repeatability, low cost and the like. The invention provides a new idea for high-speed underwater design, and the technical basis is as follows: the metal body is heated to generate a bubble air film attached to the near wall surface of the metal body in underwater motion, so that the resistance is effectively reduced, no adverse effect is generated on the environment, and specific test equipment and a method are provided.
Drawings
FIG. 1 is a schematic structural diagram of a first embodiment of a thermal surface cavitation synergistic drag reduction test device according to the present invention.
Fig. 2 is a schematic structural diagram of a metal warhead with a round head supercavity generator in the invention.
Fig. 3 is a schematic structural diagram of a metal warhead with a round-pointed-end supercavitation generator in the invention.
Fig. 4 is a schematic structural diagram of a metal warhead with a disc-shaped supercavity generator according to the present invention.
Fig. 5 is a transient high-definition image of the surface vapor development of a part of the metal body after entering water recorded by a photographic device in the test process of the invention.
FIG. 6 is the average velocity and time history data of different temperature metal bodies after entering water.
FIG. 7 is a graph showing experimental data of the resistance reduction rate of the metal body at different temperatures according to the present invention.
FIG. 8 is a schematic structural diagram of a second embodiment of a thermal surface cavitation synergistic drag reduction test apparatus according to the present invention.
FIG. 9 is a schematic structural diagram of a third embodiment of a thermal surface cavitation synergistic drag reduction test apparatus according to the present invention.
Fig. 10 is a partial right-view structural diagram in the third embodiment of the present invention.
Detailed Description
The following describes embodiments of the present invention with reference to the drawings.
Example one
As shown in figure 1, the thermal surface cavitation synergistic drag reduction test device comprises a test bed 1, an emitter 2, a metal body 3, a heater 4, a temperature measuring instrument 5, a water tank 6 and a photographic device 7. The test bed 1 may be a fixed bed that is fixedly arranged, or may be a movable bed whose height can be adjusted up and down. The test stand 1 includes, but is not limited to, a transmitter 2 installed for detachably vertically connecting a metal body 3, and in addition, the number of the transmitters 2 may be increased as needed and arranged at intervals.
In one particular embodiment, as shown in fig. 1, emitter 2 includes an electromagnet 21 and a conduit 22. The upper end of the guide tube 22 is connected to the test stand 1 and is provided with an electromagnet 21 for adsorbing the emitter 2. Specifically, the upper end of the guide pipe 22 and the upper end of the electromagnet 21 are both vertically and fixedly connected to the bottom of the test bed 1, and the upper end of the guide pipe 22 is sleeved outside the electromagnet 21. The electromagnet 21 is responsible for absorbing or releasing the metal body, and the guide tube 22 guides the released metal body 3 to ensure the falling direction thereof. The conduit 22 includes, but is not limited to, an insulating material for preventing the conduit 22 from being thermally deformed by heating the metal body 3 or the heated metal body 3. Therefore, the conduit 22 may also be made of a temperature-resistant material, so as to ensure that the conduit does not deform due to heating during the test, and a transparent material, such as high-temperature-resistant tempered glass, may be further preferably selected, so as to facilitate better observation of the metal body 3 inside the conduit 22.
As shown in fig. 1, a heater 4 is used to heat the metal body 3. In one embodiment, the heater 4 is an electromagnetic heating coil that is wound around the outside of the conduit 22. The heater 4 that can heat the metal body 3 to be varied from 100 ℃ to 600 ℃ according to the setting is preferable.
As shown in fig. 1, the temperature measuring instrument 5 faces the metal body 3 to which the transmitter 2 is connected, for measuring the temperature of the metal body 3. Preferably, the thermometer 5 is an infrared thermometer and is suspended from the bottom of the test bed 1 by a fixing frame (not shown).
As shown in fig. 1, 5, 6 and 7, a water tank 6 is provided below the emitter 2 for dropping the metal body 3 into the water tank 6 for test. In particular, the lower end of the conduit 22 should be above the water level 61 of the water vat 6. The camera device 7 is arranged facing the water vat for recording the water entry process of the metal body 3.
As shown in fig. 1 to 4, in a specific embodiment, the metal body 3 is a truncated cylinder with a length of 45mm and a diameter of 9mm. The height H of the lower end of the metal body 3 from the water surface 61 of the water tank when connected to the launcher 2 is 0.78m. The camera 7 uses a high-speed camera having a resolution of at least 2400 × 2400pi and a frame number of at least 6400 frames/s. Of course, the testing device can be equipped with or applied to the metal body 3 of the warhead with other shapes, the metal body 3 includes but is not limited to a metal warhead, the metal warhead comprises two parts of the warhead and the warhead, and the warhead with different shapes can be tested in a test mode. For example, a warhead with a round-head supercavity generator as shown in fig. 2, a warhead with a round-tip supercavity generator as shown in fig. 3, or a warhead with a disc supercavity generator as shown in fig. 4.
As shown in FIG. 1, a thermal surface cavitation synergistic drag reduction test method adopts the thermal surface cavitation synergistic drag reduction test device to perform the following operations:
(1) The metal body 3 is fixed to the bottom of the test stand 1 by the emitter 2. Specifically, the emitter 3 includes an electromagnet 21 and a guide tube 22, and a metal body is fixed on the inner top of the guide tube 22 by energizing the electromagnet 21. The metal body 3 is a flat-head cylinder with the length of 45mm and the diameter of 9mm.
(2) The metal body 3 is released by the emitter. Specifically, the electromagnet 21 is deenergized, and the metal body 3 is released. The released metal body 3 falls down the guide tube 22 and falls into the water tub 6.
(3) The water inlet process of the metal body 3 is shot by the shooting device 7, and the whole process image after the metal body 3 enters the water is obtained. Specifically, the photographic device adopts a high-speed camera with the resolution of 2400 multiplied by 2400pi and the frame number of 6400 frames/s, and the obtained whole-process image is specifically a whole-process instantaneous high-definition image of surface steam development after a metal body enters water.
(4) The metal body 3 is again fixed to the bottom of the test stand 1 by means of the transmitter 2. Specifically, refer to step (1) above, and will not be described herein again.
(5) The metal body 3 is heated to a preset temperature by the heater 4.
(6) The metal body 3 is released by the emitter 2. Specifically, refer to step (2) above, and will not be described herein again.
(7) The water entering process of the metal body is shot through the photographic device, and the whole process image of the metal body after entering the water is obtained. Specifically, refer to step (3) above, and will not be described herein again.
(8) And (4) calculating the drag reduction efficiency according to the whole process images obtained in the step (3) and the step (7).
The drag reduction efficiency is calculated specifically as follows:
processing and analyzing the whole process image in the step (5) to obtain the process time and the average speed of the unheated metal body after entering water and passing through a plurality of continuous metal body lengths, and calculating the corresponding acceleration a 1 (ii) a The resultant force F experienced is then calculated according to the formula F = ma Σ1 ；
Processing and analyzing the whole process image in the step (4) to obtain the process time and the average speed of the heated metal body after entering water and passing through a plurality of continuous metal body lengths, and calculating the corresponding acceleration a T (ii) a The resultant force F experienced is then calculated according to the formula F = ma ΣT ；
According to the formula η = (F) Σ1 -F ΣT )/F Σ1 And calculating the drag reduction rate eta.
In order to study the drag reduction rates at different temperatures, the metal body 3 is heated to different preset temperatures through the step (5), the metal body 3 heated to different temperatures is tested according to the steps (1) to (8), and the respective drag reduction rates are calculated.
In the case that the metal body 3 is a flat-head cylinder with a length of 45mm, a diameter of 9mm and a height H of 0.78m, the initial velocity v of the metal body 3 into water can be calculated 0 =3.904051m/s. And the temperature of the metal body 3 is normal temperature, 100 ℃,150 ℃,200 ℃, 8230, and 600 ℃ are respectively used for test, the history time and average speed after 1-4 times of the length of the metal body is taken to be recorded and calculated, and the results are as follows:
the instantaneous high-definition image of the surface vapor development after a portion of the metal body enters the water is shown in fig. 5.
Table 1: average speed and history time of metal bodies with different temperatures in different histories after entering water
The two-dimensional graph corresponding to table 1 is shown in fig. 6.
Table 2: resistivity reduction of the metal body at different temperatures.
The two-dimensional graph corresponding to table 2 is shown in fig. 7.
In summary, this approach can be used to quantitatively test the resistance reduction rate of heated metal bodies into water at different temperatures. In addition, the test results also show that the heated metal body can form evaporation cavitation on the hot surface in the underwater motion process to generate a bubble air film attached to the near-wall surface of the metal body, so that timely and effective drag reduction in the multi-scale complex flowing environment in water is realized, adverse effects on the environment are avoided, and an important technical basis is provided for high-speed underwater design.
Example two
As shown in fig. 1 to 8, in this embodiment, compared with the thermal surface cavitation efficiency-increasing and resistance-reducing test apparatus described in the first embodiment, the thermal surface cavitation efficiency-increasing and resistance-reducing test apparatus further includes a pick-and-place apparatus, and the pick-and-place apparatus mainly includes a two-dimensional sliding table structure 81, a collecting tray 82 and a lifting device 83.
As shown in fig. 8, specifically, the test stand 1 is provided with a bullet taking port 11 and a bullet discharging port 12, and a guide tube 22 is provided at a lower port of the bullet discharging port 12. The electromagnet 21 is arranged on the test bed 1 through a two-dimensional sliding table structure 81 and can move back and forth between the bullet taking port 11 and the bullet discharging port 12. Two-dimentional slip table structure 81 includes but is not limited to mainly by the electronic lead screw slip table 811 of the first electronic lead screw slip table 812 and the vertical setting of level setting, because electronic lead screw slip table belongs to prior art, and more specific structure is no longer described herein.
As shown in fig. 8, the collecting tray 82 is rotatably installed on the inner bottom surface of the water tub 6 by a rotating motor 821, and the upper end of the collecting tray 82 includes, but is not limited to, two spring slots 822 annularly distributed. Of course, the number of the magazine 822 can be increased or decreased as desired. The lifting device 83 is mainly used for taking out the metal warhead 3 from the bullet slot 822 and lifting the metal warhead to the position below the bullet taking port 11 so as to facilitate the electromagnet 21 to adsorb again. Preferably, the lifting device 83 is divided into an upper section and a lower section which have the same structure, and mainly comprises a vertically arranged one-dimensional electric screw sliding table 8301 and an electric clamp 8302 which is arranged on the one-dimensional electric screw sliding table 8301 and can be opened and closed, wherein the one-dimensional electric screw sliding table 8301 and the electric clamp 8302 both belong to the prior art, and the specific structure is not limited and described herein. The sectional design of the lifting device 83 can improve the working efficiency, and the upper section of the lifting device 83 can be matched with other devices, so that a new metal bullet can be put into a test, or the tested metal bullet 3 can be taken out from the test device.
As shown in fig. 1 to 8, a thermal surface cavitation synergistic drag reduction test method further includes, compared to the thermal surface cavitation synergistic drag reduction test method described in the first embodiment: get metal warhead 3 after putting the device and will go into water through the collecting tray 82 through above-mentioned, adsorb on the electro-magnet 21 of emitter 2 again behind the elevating gear 83, realize the full automatization, lifting means's work efficiency reduces the influence of human factor to the test result.
EXAMPLE III
As shown in fig. 1 to 10, in this embodiment, compared with the thermal surface cavitation synergistic drag reduction test apparatus described in the second embodiment, the test bed is arranged above the water tank in a swingable manner through a swing mechanism, and is used for changing the water inlet angle of the metal body, so as to facilitate the study of the condition that the metal body is obliquely injected into water.
As shown in fig. 1 to 10, specifically, the swing mechanism includes, but is not limited to, a connecting arm 91, a swing arm 92, a linkage shaft 93 and a driving motor 94, the swing arm 92 is disposed at both left and right ends of the test bed 1, and the other end of the swing arm 92 is pivoted with the connecting arm 91 connected to the fixed surface. The two swing arms 92 are connected to each other by a linkage shaft 93, and one end of the linkage shaft 93 is connected to a driving motor 94 for rotating the same through a gear.
In addition, the pick-and-place device includes a bucket body 84 in addition to the two-dimensional slide table structure 81, the collecting tray 82, and the lifting device 83. The bucket body 84 is fixedly installed inside the water tub 6. Specifically, the lower port of the bucket body 84 is connected to the water tank 6 through a connection member 841, and is located directly above one of the magazine 822. The upper end opening of the bucket body 84 is located below the launcher 2, and the upper end opening of the bucket body 84 is provided with a chute 842 for collecting the metal bodies 3, which is matched with the swing mechanism. The other end of the chute 842 is fixedly connected to the water tank 6. Preferably, the chute 842 is integrally formed with the bucket 84 and is transparent. Preferably, the chute 842 and the bucket 84 are both fully provided with holes (not shown in the figure) so as to reduce the resistance of the chute 842 and the bucket 84 to water after the metal body enters the water and reduce the influence of the metal body and the bucket on the test.
The above description is only an embodiment of the present invention, but the design concept of the present invention is not limited thereto, and any insubstantial modifications made by using the design concept should fall within the scope of infringing the present invention.
Claims (8)
1. A thermal surface cavitation synergistic resistance reduction test device is characterized in that: the device comprises a water vat, a test bed, a heater, emitters, a metal body, a photographic device, a temperature measuring instrument and a taking and placing device, wherein the test bed is provided with at least one emitter, the emitters are detachably and vertically connected with the metal body, and the test bed is also provided with the heater for heating the metal body; the temperature measuring instrument is used for measuring the temperature of the metal body; the water tank is arranged below the emitter; the photographic device is arranged towards the water tank and used for recording the water inlet process of the metal body;
the emitter comprises an electromagnet and a guide pipe, the upper end of the guide pipe is fixedly connected to the test bed, and the electromagnet for adsorbing the emitter is arranged; the heater is an electromagnetic heating coil and is wound on the conduit;
the taking and placing device comprises a two-dimensional sliding table structure, a collecting disc and a lifting device, the test bed is provided with a bullet taking port and a bullet discharging port, and the bullet discharging port is provided with the guide pipe; the electromagnet is arranged on the test bed through the two-dimensional sliding table structure and can move back and forth between the bullet taking port and the bullet placing port, the collecting disc is rotatably arranged on the inner bottom surface of the water tank, and at least two bullet grooves are annularly arranged at the upper end of the collecting disc; the lifting device is used for taking out the metal bullet from the bullet groove and lifting the metal bullet to the bullet taking opening.
2. The hot surface cavitation synergistic drag reduction test device of claim 1, characterized in that: the test bed is arranged above the water cylinder in a swinging and adjusting mode through a swinging mechanism and used for changing the water inlet angle of the metal body; the swing mechanism comprises a connecting arm, a swing arm and a driving motor, the swing arms are arranged at the left end and the right end of the test bed, and the other end of each swing arm is pivoted with the connecting arm connected to the fixed surface; the two swing arms are mutually connected through a linkage shaft and are provided with the driving motor for rotating the linkage shaft; the taking and placing device further comprises a bucket body, the bucket body is arranged inside the water tank, the lower port of the bucket body is located right above the elastic groove, the upper port of the bucket body is located below the emitter, and the upper port of the bucket body is provided with an inclined groove body matched with the swing mechanism and used for collecting metal bodies.
3. A hot surface cavitation synergistic drag reduction test method, characterized in that the hot surface cavitation synergistic drag reduction test apparatus as claimed in claim 2 is used to perform the following operations:
(1) Fixing a metal body at the bottom of the test bed through a transmitter;
(2) Heating the metal body to a preset temperature by a heater;
(3) Releasing the metal body by the emitter;
(4) Shooting the water entering process of the metal body through a photographic device to obtain an overall process image of the metal body after entering the water;
(5) According to the steps (1), (3) and (4), obtaining an image of the whole process of the unheated metal body at normal temperature after being put into water;
(6) And (5) calculating the drag reduction efficiency according to the whole process images obtained in the step (4) and the step (5).
4. The hot surface cavitation synergistic drag reduction test method according to claim 3, characterized in that the drag reduction efficiency is calculated specifically as:
processing and analyzing the whole process image in the step (5) to obtain the process time and the average speed of the unheated metal body after entering water and passing through a plurality of continuous metal body lengths, and calculating the corresponding acceleration a 1 (ii) a The resultant force F experienced is then calculated according to the formula F = ma Σ1 ；
Processing and analyzing the whole process image in the step (4) to obtain the process time and the average speed of the heated metal body after entering water and passing through a plurality of continuous metal body lengths, and calculating the corresponding acceleration a T (ii) a The resultant force F experienced is then calculated according to the formula F = ma ΣT ；
According to the formula η = (F) Σ1 -F ΣT )/F Σ1 And calculating the drag reduction rate eta.
5. The hot surface cavitation synergistic drag reduction test method of claim 3, characterized in that: in the step (1), the emitter comprises an electromagnet and a guide pipe, and the metal body is fixed by electrifying the electromagnet; in the step (2), the heater is an electromagnetic heating coil wound on the conduit; in the step (3), the electromagnet is powered off to release the metal body, and the metal body falls down along the guide pipe; in the step (4), a high-speed camera is used as the photographic device for shooting, and instantaneous high-definition images of the whole process of surface steam development after the metal body enters water are obtained.
6. The hot surface cavitation drag reduction test method of claim 3, 4 or 5, further comprising: and (4) respectively testing the metal bodies heated to different temperatures in the mode of the steps (1) to (4), and respectively calculating the respective drag reduction rates.
7. The hot surface cavitation drag reduction test method of claim 3, 4 or 5, further comprising: the metal warhead after entering water passes through the collecting disc through the taking and placing device, and is adsorbed on the electromagnet of the emitter again after the lifting device.
8. The hot surface cavitation drag reduction test method of claim 3, 4 or 5, further comprising: the angle of the test bed is changed through the swing mechanism, and the water inlet angle of the metal body is further changed.
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