Chapter 612 The collision of two wall-mounted minds

The reason why Song Wencong specifically brought up the topic of bow shock waves was mainly because he was worried that the treatment of this area would affect the overall project progress.

After Chang Haonan determined the follow-up improvement direction of the J-10 last year, the Project project team did not wait for support, but quickly began to carry out some pre-research work based on the two existing prototypes.

Because wind tunnel testing alone cannot completely restore all phenomena that occur on real machines.

Although the JJ-9 has a lot of flight hours, the supersonic capability of that model can basically only be used to give students flight experience. It is difficult to find actual problems with the DSI inlet under high-speed flight conditions. .

Moreover, it is designed with air intake on both sides, so it is not easily affected by the pre-compression of the incoming machine head.

In this way, we discovered the problem of enhanced boundary layer separation induced by bow shock waves that had not been paid attention to in the past.

Anyone who often works on projects will know that the simple and complicated parts are not terrible. The most troublesome thing is that a problem that has never been considered before suddenly appears halfway through.

It is very likely that a single move will affect the entire project, and may even cause the entire project to be drastically changed or even terminated directly.

Although the trouble at hand is not that big, as long as enough time (and computing power, of course) is given, it can be solved anyway.

But what Project No. 10 lacks most right now is time.

Therefore, Song Wencong had even made a plan.

If it really can't be done in a short time, then let Project 10 serve with its current structure first and solve the Air Force's lack of third-generation fighter jets as soon as possible.

As for the improvement ideas proposed by Chang Haonan, we can talk about it later.

Anyway, the Chinese Air Force is not small and can accommodate enough sub-models.

However, now that Chang Haonan had given out the solution almost without thinking, everyone around him immediately felt at ease.

This at least shows that the former has been mentally prepared for this.

"It turns out...Comrade Haonan has even studied such technical details?"

Compared with others, Yang Wei, who was standing next to Chang Haonan, had more disbelief in his tone:

"This foresight and foresight is really admirable..."

"Uh... Actually, it's not foreseeable. It's just a coincidence..."

The former was so praised that he quickly waved his hand.

Then, he saw several curious eyes around him.

After a short pause, he had no choice but to explain:

"I published a paper on the mandibular adduction airway the year before last. You should know that, right?"

The other people naturally nodded.

Although everyone has been a veteran of Project 7 since the beginning (except Chang Haonan), no one has personally participated in the development of the J-F.

But the article "Research on the Integrated Layout of Dual-Module Mandibular Inward-Turn Inlet/Conical Forebody" is a classic document of computational fluid dynamics, and Lu Yuying specifically mentioned it in many conferences for a while. I've definitely seen all the content.

"Actually... I discovered at that time that if the position of the air inlet is further modified, when it reaches the belly position, after the incoming flow speed exceeds the factor, the boundary layer will be very unstable, and a slight disturbance will will be separated."

"I see……"

Song Wencong also suddenly realized:

"No wonder you designed the combination of the conical front body and the air intake duct to be so... special. It turns out that the key point is this..."

The so-called special is naturally a euphemism for ugly.

It must be admitted that the design of the J-7F is indeed poorly thought out in terms of appearance.

"Is this..."

In fact, Chang Haonan just found a random reason.

In fact, he knew about the bow shock wave because he had read relevant technical information in his previous life.

As for the solution, I really only started thinking about it after coming into contact with Project No. 10.

Because the J-10 solved this problem in the previous generation around 2010. With the computer computing power at that time, when solving the shape of the DSI air inlet cocoon, it was even possible to directly add an extra degree of freedom for optimization.

But without this condition now, we can only use some tricky methods.

Who would have thought that after just one operation, even Song Wencong would feel a little enlightened.

But it was impossible for him to tell the truth, so he had to skip the middle process and concluded vaguely:

"In short, I have been studying this issue since that time. Later, when I participated in the 83rd Project to improve the wings of the aircraft, I came up with the idea of ​​using vortex generators to delay the separation of the boundary layer."

"Moreover, in addition to this main function, a well-designed vortex generator can also improve the flow field quality at the inlet outlet and reduce the total pressure distortion at the inlet of the turbofan engine."

This part of the content can be said to be watertight.

On the one hand, the technicians around Rongfei didn’t know what happened in the 83rd Project.

On the other hand, there is indeed some theoretical connection between the vortex generator and the wing knife...

If you insist on forcing me to do it forcefully, it makes sense.

"hiss--"

As his words fell, a uniform sound of inhalation suddenly sounded around him.

You know, although Chang Haonan, including those closest to him, such as Ding Gaoheng, Du Yishan, etc., are a little numb to these things, others are not yet.

In the eyes of others, doesn't the explanation just shown that others began to think about such complex issues in their junior year?

Isn't that why the strong men of Douzong are so terrifying?

This joint is actually not easy for Chang Haonan to figure out.

However, he also felt that he should change the topic.

Fortunately, Yang Wei next to him gave an assist at this time.

After all, his evolution is quite outrageous to some extent.

When people of the same kind see the same kind, they are naturally more receptive.

Therefore, while others were still shocked by Chang Haonan's inhumanity, he had already begun to follow Chang Haonan's thinking and consider technical issues:

“From a qualitative point of view, on the one hand, the vortex generator enhances the momentum exchange between the low-energy fluid near the wall and the mainstream to achieve the effect of inhibiting separation, but on the other hand, it also increases the inlet resistance loss, which is considered a design The choice?"

Seeing that the technical topic was finally back to conversation, Chang Haonan secretly sighed in his heart that he was indeed a real boss. The agility of his thinking was close to physical cheating, and he nodded immediately:

"It is indeed the case. At supersonic speed and high incoming flow Mach number, the shock boundary layer interferes seriously, leading to large flow separation. At this time, the benefits brought by the vortex generator to suppress separation are more obvious, which is reflected in the total pressure recovery coefficient It’s just that the loss is smaller.”

"Correspondingly, at low inflow Mach numbers, the separation is relatively small, and the resistance loss of the vortex generator is more obvious, which is reflected in the greater loss in the total pressure recovery coefficient."

“So, the design of this vortex generator and the selection of parameter indicators are very important. Fortunately, the total pressure recovery coefficient of the DSI inlet at low speed is almost at a surplus level, and we don’t care about a slight loss, so the optimization window is not It’s pretty strict.”

"Also, under certain electromagnetic wave incident angles, the eddy current generator will increase the radar reflection area and destroy the stealth performance."

"The problem of invisibility is not that big..."

Another deputy chief designer next to him smoothed his gray hair:

"Although the DSI air intake can reduce a certain amount of RCS, if the overall design does not systematically consider low detectability, the benefits brought by just a few detail corrections are not large, so I don't care about this percentage. Quite a few changes.”

"It's just... I was just thinking about whether similar ideas can be applied to other models. It seems that I want to keep it simple..."

This sentiment immediately aroused a burst of recognition.

However, Yang Wei's focus is obviously at a higher level than others:

"Wait...if you think about it from another angle..."

"According to our current practice, the comprehensive distortion index only includes circumferential distortion and turbulence components. However, in the design of DSI inlet ducts that include vortex generators, radial distortion and swirling distortion also need to be systematically considered. Case."

"Maybe we should take this opportunity to change our design habits..."