Chapter 309 Boss Yang Wei’s shock

Having said this, Chang Haonan stood up directly, came to the side of the curtain, and said while gesturing on the picture:

“In fact, we can see from this picture that the closer the area is to the instability boundary, the higher the compressor boost ratio. The higher the boost ratio and the higher the efficiency, the higher the performance of the engine. However, the existence of the instability control line prevents the engine from operating in the area between the instability boundary and the instability control line. Most of the time, the engine can operate stably in this area. It can be seen that the existence of the instability control line actually This prevents the engine's performance from being fully utilized."

"The short-term stability augmentation system is a form of open-loop control and requires the pilot to manually turn it on. This means that pilots with relatively conservative flying habits may activate the system before the engine actually reaches the instability control line, further reducing the engine speed. Performance potential, and pilots with aggressive flying habits may not turn on this system until the engine has entered a state of aerodynamic instability. Often, at this time, the engine's working condition has begun to be damaged and enter an irrecoverable stall, which greatly affects flight safety. discount."

After explaining the shortcomings of this traditional method, he sat back in his seat and clicked the mouse to release the next page of PPT:

“So when I was working on the 83rd Project last year, I began to consider whether we could use a more precise method that would have less impact on engine performance to control engine stability. Finally, I summarized two new methods not long ago. The methods are stability seeking control and active surge control."

"The former integrates the engine stability check into the engine's control system and determines the instability control line position through real-time assessment of engine stability, rather than the worst-case scenario assumed during design, allowing the control system to minimize the stability margin. , thereby improving engine performance.”

"And the latter... Before introducing active stability control, please allow me to mention a new concept named by myself - surge precursor."

"Surge sign..."

A light seemed to flash in Yang Wei's eyes:

“Are you trying to predict surge in real time?”

It can only be said that the boss is the boss. Although he was facing a completely new concept, he still realized what Chang Haonan was going to do in the shortest time.

The few people who followed Yang Wei immediately showed expressions that were almost horrified.

The essence of surge is a positive feedback self-excited process. That is to say, once a certain part starts to surge, unless it is stopped and restarted immediately, the surge will be "infected" to the entire system in a very short time. inside the engine and cause irreparable damage.

In other words, for traditional methods, when you detect abnormal engine data, it is actually too late.

Accurately predicting surge is orders of magnitude more difficult than accurately predicting weather!

In fact, even after surge has occurred, it is quite difficult to reversely find the operating point that induces surge from the data recorded by the engine control system.

Chang Haonan himself should have some experience of this.

So……

How much fluid mechanics knowledge do you need to boast that you can predict surge in real time?

"Yes."

Faced with Yang Wei's question, Chang Haonan just nodded lightly and replaced it with another picture:

“After analyzing and summarizing a series of surge failure data that occurred on the J-8 and J-H7 aircraft, I noticed that during the stall initiation process before the surge occurred, there were some small amplitude The disturbance waves are formed from the stable flow field, and their influence is very weak. It is almost impossible for the pilot to intuitively feel it. However, if there is no interference with the working state of the engine at this time, these disturbance waves will continue to strengthen and start at the beginning. At the end of the process, it turns into a rotational stall, which then develops into surge, so I call these disturbance waves surge precursors.”

“Therefore, my idea is to detect these surge precursors through a series of sensors and waveform processing technology, and then add additional disturbances to the flow field to suppress the formation or development of stall precursor waves and delay the occurrence of rotational stall.”

When Chang Haonan talked about this, the other people looked at him as if they were a monster.

It is equivalent to a person saying that I not only want to accurately predict the weather at a certain time six months from now, but I also want to control the weather at this time through technical means.

This theory sounds a bit like extreme tightrope walking, let alone its direct application in the engineering field.

The four words safety margin are almost the core element of engineering design, and Chang Haonan actually directly stated that he wanted to keep the safety margin to the lowest while ensuring the highest safety...

All I could do was gasp.

As for the boss, he once again showed how extraordinary he is.

Yang Wei touched his chin and pondered for about half a minute, and the first reply he gave was:

"I actually did some research on this surge prediction before."

This time it was Chang Haonan's turn to be shocked.

"You are too young, so you may not know, but many old people in the 611 Institute know that around the 90s, because they were all engaged in civilian industry, I didn't think it was interesting, so I very seriously considered working abroad. "

Chang Haonan was even more shocked.

You have to keep this shit, otherwise the losses will be incalculable...

"Anyway, during that time, I paid attention to some cutting-edge research done by foreign universities, which was... quite far from engineering. Two professors named Moore and Glazer proposed an axial-flow compressor to rotate. The stall state model includes three physical quantities: flow coefficient, pressure coefficient and rotational stall amplitude, and is generally called the MG model."

What was said later did not exceed Chang Haonan's expectations.

This MG model is basically the starting point for all surge prediction research.

After a short pause, Yang Wei continued:

"This model is relatively easy to use in academic research and small experiments, but when it comes to the engineering field, three physical quantities bring three systems of partial differential equations, and the degree of nonlinearity is very high. I once asked a friend who specializes in mathematics After consultation, he said that I could use one called..."

"Galerkin method?"

All this has entered Chang Haonan's rhythm.

"Yes, the Galerkin method, and then select a cubic curve as the characteristic curve, convert the system of partial differential equations into a system of ordinary differential equations and then solve it. But I personally tried it and found that the amount of calculation is unimaginable. Moreover, the accuracy of the final results is not high. In short, there is no application potential so far..."

After listening to this introduction, Chang Haonan felt a little ashamed and said to himself that you can't call this a little research at all. You have already done half of my work...

But on the surface, he just coughed twice:

"Actually, the MG model you just mentioned is the starting point of my entire idea."

"It's just that I have recently produced some research results on numerical solutions to strongly nonlinear partial differential equations, which can be used in the optimization and subsequent solution process of the MG model."

Yang Wei, who had been calm and composed just now, finally couldn't stand it any longer.

"Do you still have research on mathematics...?"