Changan uni-t China Automotive Research Laboratory tests and explores the secret of low wind noise

On September 16, Chang’an uni-t, together with Qin Yong, project director of Changan uni-t and sun Luo, an international senior expert in the field of aerodynamics and thermal management, explored the mystery of wind noise at the aerodynamics acoustic wind tunnel laboratory of CAAC. There are not only eye opening 3D acoustic camera “catching wind and sound”, but also interesting links such as on-site clay model making and smoke flow testing, which fully decrypts the hard core scientific and technological strength behind the future design of Chang’an uni-t. < / P > < p > Chang’an uni-t positioning compact SUV meets the diversified needs of young consumers. For them, the car is not only a means of transportation, but also to meet their aesthetic and emotional needs. Chang’an uni-t responds to these demands one by one through new design, powerful intelligent vehicle system, new blue whale power and platform architecture, and L3 level automatic driving technology. Changan uni-t provides consumers with new choices and unforgettable experience. < / P > < p > in the process of driving a car, there are often various noises, such as engine noise, road noise and tire noise. In the process of driving, the noise generated by the interaction between the shape and contour of the body surface and the airflow is called wind noise. The faster the car runs, the greater the wind noise. Once the vehicle speed exceeds 80 km / h, wind noise will gradually overshadow other noises and become the main noise source. In the latest survey of automobile consumers, the complaints about wind noise rank top 5, which has become one of the most dissatisfied problems of automobile users. Wind noise is not only wide frequency band, but also high intensity. It is easy to make passengers feel irritable and tired. It will also endanger the driving safety if it is affected by the wind noise for a long time. At the same time, due to the promotion of green city construction and the popularity of new energy vehicles such as electric vehicles, the problem of wind noise becomes more and more prominent. In order to study wind noise comprehensively and systematically, two environmental conditions must be met. One is the wind source with stable flow field and accurate and controllable wind speed; the other is that it can eliminate the interference of other noises. The wind tunnel laboratory is undoubtedly the best choice. Sound absorbing materials are installed on the surrounding walls and top. Acoustic treatment and pressure fluctuation adjustment are used in the flow channel to reduce the background noise to a very low level. When the wind speed reaches 140km / h, the ambient noise is only 58 dB, which is one of the quietest wind tunnels in the world. < / P > < p > microphone array, also known as “acoustic camera”, is equipped with 168 microphones on the upper, left and right sides, so that the array can accurately identify the external sound source. The 3D distribution of the noise source on the surface of the car body can be obtained by shooting the acoustic cameras on the top and both sides at the same time, and then through the computer matching and synthesis. China Automotive Research wind tunnel laboratory is the first wind tunnel laboratory equipped with three microphone array in China. It is one of the most advanced acoustic measurement equipment in the world. < / P > < p > hold two paper clips with an interval of 5cm. From a height of about 1.5m, you can see two small color blocks in the monitoring screen of the acoustic camera, which shows the high sensitivity of the acoustic camera. At the same time, it is also very accurate. Even if the two sound sources are very close, they can be clearly identified 。 The reliability of vehicle noise source identification and test is guaranteed. < / P > < p > the artificial head is mainly used to collect the real noise that people feel when they are in the car. In the test, it will be placed on the front driver’s seat and the co driver’s seat. An acoustic sensor is installed at the position of both ears of the artificial head, which can simulate the impact of human shoulder, head and auricle on the sound field when recording sound, and playback the sound signal closer to the actual human ear. < / P > < p > the surface microphone is attached to the body surface to measure the pressure fluctuation on the body surface. The purpose of the three devices is to help get the most comprehensive data in the wind noise experiment, find out the problems and improve them. < / P > < p > after the test is started, the wind speed should be adjusted to the speed required by the test. During the wind noise test, the wind speed is usually set at 80-140km / h per hour, and the wind speed during live broadcast is set at 120km / h. The acoustic camera and artificial head usually collect about 30 seconds of data. After the acquisition, the computer will further process the original data and obtain the To the information you need. < / P > < p > the single-sided array has 168 microphones, and the three-sided array can collect 504 channels of sound signals. The amount of data is very large, and it takes some time to process these data. But the artificial head only collects dual channel signals, so the processing time will be much faster. < p > < p > we can see that the wind noise of uni-t test is different under different wind speed and frequency band. We can judge the size of noise source through the noise screen spectrum, and the feeling of different frequency band is different. Overall, uni-t wind noise test results in the industry is in a relatively good level. < p > < p > at the beginning of the design, uni-t analyzed the aerodynamic performance of different modeling schemes through CAE simulation, so as to find problems and improve the design. Through the sludge model, the actual test and further shape adjustment were carried out. < / P > < p > for example, the wind noise optimization of rear-view mirror only involves multiple departments such as modeling, regulations, CAE and products. Whether the shape is good-looking, whether the vision meets the requirements of regulations, and whether the wind noise after final adjustment can meet the requirements of the regulations needs cooperation and cooperation with multiple departments. A small change requires the joint efforts of countless people behind. Through the optimization of rearview mirror, the total sound pressure level at the driver’s ear is reduced by 0.3dB (a), which shows the technical strength of Changan CFD. On uni-t, such countless details are optimized, and the 0.3dB (a) of each one will add up to many, and eventually qualitative changes will occur. As one of the landmark designs of uni-t, the tail design of uni-t is very special. Such advanced design also brings great challenges to the CFD team. After all, from the perspective of aerodynamics, it is inclined to let all the car models be designed in the same way, but this is obviously not what consumers want to see. Therefore, the mission of aerodynamics people is to make the shape design of different shapes have good aerodynamic performance. < / P > < p > due to the hollowed out design of the rear wing, the air flow from the roof will impact down on the rear window through the holes and v-channels, resulting in large wind noise. When we first saw the design, the CFD team held an emergency meeting to repeatedly demonstrate the feasibility and risk, and called 4000 core simulation computing resources, with the calculation amount of more than 1 million CPU hours. If it is replaced by a high-performance personal computer processor on the market, it will take more than 12 years of non-stop computing, while the 4000 core high-performance computing server can compress the whole computing cycle to 20 days. More than 60 optimization schemes are calculated before and after, and more than 20 effective schemes are found, which greatly reduce the wind noise generated by the tail. < p > < p > smoke flow test is the most common test method in the flow visualization test. After the sludge model engineer uses the sludge to restore the early V-shaped tail design, the influence of different tail shapes on the flow field can be seen through the smoke flow test. < / P > < p > in the early tail design, due to the negative pressure generated at the rear of the car, part of the air flow goes down from the hollow part of the tail wing, forming turbulent flow and generating large pressure pulsation, which is transmitted to the vehicle through the rear windshield, which brings about greater wind noise; although the final commercial vehicle tail state on the other side is also hollow design, when the air flow passes through the rear of the roof, the canard tail will raise the air flow, and then the rear part of the car will rise A slope is formed on the tail to guide the air flow better. The trend of the airflow hitting the rear window is alleviated, and the wind noise is effectively reduced. At the wind speed of 120 km / h, uni-t still achieved good wind noise test results. Behind such achievements, it not only embodies the wisdom of uni-t design team and engineers, but also reflects Chang’an Automobile’s unremitting pursuit of creating the ultimate product force with user experience as the center, and brings more comfortable and perfect driving experience for consumers.