Coquettish Rebirth

This time Jia Hongjian and his SUV model blow in the wind tunnel, which is no longer the same as when the Soviet national car was introduced in the past, and it was necessary to go to the wind tunnel of the aircraft.In these years, Huaxia Hi-Tech has established its own wind tunnel test base in the suburbs of Shanghai!In such an experimental base, it has a series of test items such as a model wind tunnel and a real car wind tunnel, and it is now the only wind tunnel dedicated to automobiles in China!Such a wind tunnel was originally invested by Huaxia Automobile, and found the world's leading automotive wind tunnel design organization, Germany's wbi company, and then cooperated with the Electromechanical Design and Research Institute in Shanghai to invest a total of 5 million yuan, covering an area of ​​about 213 Mu, with a total construction area of ​​21095 square meters.

In the wind tunnel building, there are two large wind tunnel workshops.One workshop is an aero-acoustic wind tunnel and the other is a thermal environment wind tunnel.Judging from the names, the two wind tunnels have different functions.To put it bluntly, the aeroacoustic wind tunnel is to test the wind resistance and wind noise and other items. The car not only needs to have low wind resistance, but also cannot have any external design that makes the wind noise particularly loud. The inside of the car must also be silent!The nozzle area of ​​this wind tunnel reaches 27 square meters. It is equipped with an axial flow fan manufactured by Shanghai Blower Factory. Cubic meters, which is equivalent to the air output of nearly 4125 ordinary household ceiling fans!That much power can accelerate still air to 110 kilometers per hour in just 8.5 seconds.In the test section, when the wind speed is 195 kilometers per hour, the background noise is only 1920 decibels, which is currently the quietest among automobile wind tunnels of the same scale in the world!

As for the thermal environment wind tunnel, it is mainly used for vehicle thermodynamic testing and thermal environmental performance evaluation. It has variable-sized nozzles of 7-14 square meters and is equipped with a 1600-kilowatt fan manufactured by Shanghai Blower Factory.The diameter of the impeller is 4 meters, the total weight is 24 tons, the speed is 740 revolutions per minute, the air volume is 390 cubic meters per second, and the maximum wind speed in the test is 0-200 kilometers per hour.Although it seems that the performance is not as good as that of the fan in the aeroacoustic wind tunnel, this thermodynamic fan can produce wind with a temperature of minus 20 to 55 degrees.At the same time, the humidity can be controlled from 5% to 95%!It is also equipped with a full-spectrum sunlight simulation device with variable intensity and angle and a dual-axis drive drum system, simulating sunlight of 300-1200 watts per square meter.It can simulate various climatic conditions and vehicle driving conditions such as sun exposure, wind and rain, ice and snow frost.

After completion and opening, the Wind Tunnel Center will not only be able to carry out a series of tests on complete vehicles and parts of cars, buses, suvs, trucks, etc. experimental conditions.Through the wind tunnel test, it can provide first-hand data for optimizing the shape of the vehicle during the design process, reducing fuel consumption, improving vehicle driving safety and handling stability, controlling aerodynamic noise inside and outside the vehicle, and optimizing the engine cooling system and air conditioning system. , so as to complete vehicle model development, modified design, and thermodynamic performance evaluation in a relatively short period of time.According to the results of international research.On average, when a car is driving, almost 40% of its fuel consumption is used to fight against wind resistance, and when the car reaches a speed of 120 kilometers per hour, 60% of its fuel consumption is used to fight against wind resistance!If the wind resistance is reduced by 10%, then the fuel consumption can be reduced by 3% to 6%!This is true for gasoline locomotives, and it is naturally true for our electric vehicles.If the aerodynamic wind resistance is better optimized in terms of styling, naturally the short board of our battery power can be made up for.Wouldn't it be possible to increase the cruising range?

The process of such a blowing tunnel is the same as what Jia Hongjian said before.It is not to blow the whole car directly, but to blow the model first.As for the blowing model, there are also large and small models. The smallest is a miniature scale model made of oil clay. When this kind of blowing is done, it is not blown in a large wind tunnel, but placed in a small one similar to an extended n A lot of transparent shoe boxes blown inside.This isometric miniature model.Although it seems that after reducing the ratio, the test data may be slightly worse than the real car due to various reasons, but on the one hand, it saves money, and on the other hand, it can also be placed in this "transparent shoe box" Conduct some "liquid wind tunnel" experiments.This so-called "liquid wind tunnel" is actually a method of using liquid to replace the air in the wind tunnel. Such a method is often used to test the model of the aircraft-because when the speed reaches a certain level.In fact, air is not much different from a viscous liquid for an airplane!

Of course, our car does not need to put liquid in the wind tunnel. After all, the fastest speed of the car is one or two hundred. The difference between air and water and other liquids at this speed is quite big.Put the scale model made of clay into the plastic box, seal the lid, and then exit the laboratory, the operators outside the laboratory will start to operate the machine and blow the air in the plastic box.During the blowing process, the wind also carried a few white smoke straightly blowing towards the model.The miniature scale blowing tunnel is actually blowing in this way. The smoke does not dissipate after being blown out, but keeps its own line straight and straight just like when it was blown out.After the smoke blows onto the car model, it starts to be disturbed.

Outside the laboratory, Jia Hongjian could see the scene captured by the camera in the laboratory, and then a lot of data was displayed on the computer screen in front of the operator next to him.What these data are, Jia Hongjian doesn't need to understand, he is not a professional, he is the boss!How much do you need to know as a boss?Soon, the result of the blowing tunnel of the model came out—it was not very ideal, mainly because the front part of the car was streamlined, but it was hand-designed by Jia Hongjian after all, which still caused a little turbulence.At the same time, due to the structure of the roof and the rear of the car, there is more turbulence at the rear of the car, which leads to increased wind resistance.During such a process, Jia Hongjian communicated with the professional designers of Huaxia Automobile, and he also learned several key aspects of the source of wind resistance in the design of the car's shape. Generally, there are three forms of air resistance. The first is the impact of airflow on the vehicle. The resistance generated by the front is like holding a wooden plank against the wind, and the resistance encountered is almost all the resistance generated by the impact of the airflow.After the car is designed to be streamlined, the resistance generated by this frontal impact on the airflow can be reduced a lot.

The second type of wind resistance is frictional resistance. The air will generate frictional force just like passing through the car body. However, at the fastest speed that a general vehicle can drive, the frictional resistance is so small that it can almost be ignored.The third is external resistance, which is the main source of air resistance when the vehicle is running at high speed.The resistance caused by the appearance comes from the vacuum area behind the car. The larger the vacuum area, the greater the resistance.Generally speaking, the appearance resistance of a sedan is smaller than that of a hatchback, and the one with the least resistance should be made into the shape of a peach pit.This kind of vacuum area is actually a vortex area. To put it simply, it is a bit like the white mark of the waves left behind after a ship sails through the sea.When a car moves through the air, it splits the air to the left, right, and up and down.At the same time, the car is not as flat as a knife, and its shape still has ups and downs, so the cut air will rise and fall along the car's appearance, just like the water in the river meets the streamlined pebbles.But when the air travels to the rear of the car, it is like a stream of water flowing over pebbles, and there will be a recovery process-after all, it was cut open before, and it is easy to produce gas in this recovery process. Vortex, while creating a "vacuum zone" with relatively low air pressure.

The calculation of wind resistance is also very simple - when the car is blown in the wind tunnel, the wind speed represents the speed of the car, after all, the car is stationary.And the car is fixed, not because the wheels are directly locked on the ground, but a small pillar with sensors is placed under the four wheels.This small pillar can sense how much lateral force it receives when it is holding the car to blow the wind!And such a horizontal force is actually the resistance of the wind when the car is driving if there is no small pillar!So in fact, such a wind resistance figure is measured by the blowing tunnel, and the wind resistance figure is brought into the calculation formula to obtain the so-called wind resistance coefficient!There is nothing particularly magical about such a formula of drag coefficient - frontal drag = drag coefficient x air density x frontal projected area x square of vehicle speed and then divide the total by 2.

According to the results of such a blowing tunnel, the designers of Huaxia Automobile will then modify the front of the clay model on the spot, and then send it into the blowing tunnel.According to the results of the wind tunnel, the details of the car model are continuously optimized. The optimization of the following designers is mainly on the details of the appearance, such as various eddy currents caused by the exterior rearview mirror, and the angle of the windshield. Because of the tilt angle of the windshield, it is actually easy to cause the wind to directly hit the windshield, so the resistance is naturally large!As for Jia Hongjian himself, he began to pay attention to such a structural problem as a hatchback!Hatchbacks have greater resistance than sedans. The main reason is that sedans have a tail that collapses in the end while hatchbacks don't.With a collapsed tail, the airflow cut by the roof can be "pacified" as much as possible, so that the airflow will "not disturb".As for the hatchback, just cut the airflow, don't care about "pacification", isn't the airflow trying to cause trouble?

So is there any way to reduce this messy airflow?For example, on large trucks, Jia Hongjian saw a curved strip protruding from the roof of many large trucks. What is such a strip used for?Is it for spoilers?Is it just to "pacify" the airflow? (To be continued..)