Chapter 84 Unstable Work Line

The first step in this task, which is also the core step, is to find the common working conditions of each component of the turbojet 14 engine and establish a common working equation.

It happened to be the part that Chang Haonan probably knew how to do.

So he found Lin Gang, the person in charge of Yan Liang, borrowed a workstation from the flight test institute, and entered into a selfless working state.

Time is everything now. In order to improve efficiency, the system must be used to help.

Therefore, the top priority is to clarify the complete solution to the entire problem in order to form a project in the system.

Thinking of this, Chang Haonan pulled out a piece of draft paper from the side.

The calculations related to flow separation in turbomachinery are quite complex and are not his strongest area, so it is safer to write about it.

Directly analyzing the engine component-level mathematical model is definitely not something that computers of this era can accomplish, and it is not necessary. Therefore, the second step should be to reasonably simplify the model.

"(1) Continuous flow between components"

Chang Haonan wrote the first principle on paper.

"(2) Power balance of compressor and wheel on the same shaft..."

"(3) The rotational speeds of the compressor and turbine on one shaft are equal..."

"(4) When the tail nozzle is operating subcritically, the static pressure at the far front and at the nozzle exit section is atmospheric pressure. Therefore, the pressure change in the engine flow channel should meet the conditions of balancing the degree of supercharging and expansion..."

"..."

Every time he writes a few pieces of content, Chang Haonan will make an attempt.

After he used the fourth piece of paper, the system finally responded:

[Technology points consumed to improve the project: 10 points. Points consumed to directly give the project results: 100 points. Are you sure to carry out the unstable working line calculation project of the turbojet 14 engine? 】

"It finally happened..."

Chang Haonan slowly took a deep breath.

"Confirm! Complete the project!"

……

The whole night passed quickly.

When the morning sun slowly rose from the horizon the next day, the joint power research team, led by Yan Zhongcheng, finally completed the dimensionlessization of the test flight data and the drawing of the surge waveform curve.

The next task is to find the position that first induces the abnormality from the large number of complicated curves.

The main implications of this work are twofold.

First, it can provide directional guidance for subsequent high-altitude station simulations and try to reproduce the fault.

The main purpose is to determine the cause of the surge, whether it is a design flaw, a manufacturing flaw, or simply too poor air intake conditions.

Second, if the compressor needs to be improved later, then this surge-inducing position will be the starting point for modification.

Of course, engine design is a matter that affects the whole body, but no matter how complicated the work is, there will be a starting point.

Just like the thread in a ball of wool.

"Gong Yan, why don't you go take a rest first?"

A young engineer looked at Yan Zhongcheng, who was carefully checking the data and his eyes were red, and asked with concern.

The latter held his waist with one hand and held the mouse with the other hand to mark several abnormal operating points on the boost coefficient and flow coefficient diagrams of the compressor. He directly rejected the proposal without looking back.

"No, at least we have to find out the problem first. It shouldn't take long."

For him, who is experienced, this job is not particularly difficult.

As time passed, the ins and outs of the surge problem became increasingly clear in Yan Zhongcheng's mind.

"You all come here."

He waved his hand behind him and summoned several other engineers who were in the same room with him.

"By the way, why don't you see Dr. Chang who came with us?"

Because I stayed up all night processing data, and Chang Haonan was not a member of the power joint research team, it would not be a waste to miss him when working, so it was not until Yan Zhongcheng sent a message to everyone to come over that everyone realized the lack of a person.

"Yeah, it seems like I haven't seen anyone else since last night."

"You didn't run away to rest by yourself, did you?"

"Forget it, let's go look for him later. Let's listen to Yan Gong's assignment first."

Everyone gathered around Yan Zhongcheng and looked at the enlarged data graph on the CRT monitor.

The latter picked up a pencil from the side, gestured on the screen and said:

"You see, I have separated out the surge oscillation ring separately. The above OA, AB, BR and RO are the four stages of operating conditions in the surge process."

"When external disturbances cause the compression system to enter a surge state, in the first part of the OA, because the pressure rise provided by the compressor cannot balance the pressure established in the rear part, under the action of strong back pressure, the pressure flows through the compressor The gas flow rate drops sharply, but due to the lag of dynamic response, the pressure behind the compressor changes slowly. In some cases, such as when the compressor pressure is relatively high, the instantaneous flow rate of the compressor can be reduced to zero, and even reverse flow occurs. .”

"When the instantaneous flow reaches the minimum value of point a, corresponding to the system pressure at the rear of the compressor, since the flow flowing in through the compressor is much smaller than the flow flowing out through the pressure regulating valve, in the second part of AB, the flow flowing into the compressor The flow continues to increase while the pressure in the rear gradually decreases.”

"..."

"For the current valve opening, the instantaneous flow rate at point R is undoubtedly too large. That is to say, the pressure rise that the compressor can provide at this time is much less than the pressure drop required by the pressure regulating valve for the same flow rate. Therefore, the pressure regulating valve is Under the restriction, the flow rate through the compressor must be reduced again, while the pressure at the rear of the compressor continues to rise, and the instantaneous operating point of the compression system is closer to the original stall starting point O from R."

The biggest difficulty of this work is to find and separate the oscillation ring. Now that Yan Zhongcheng has completed this step, other young people in the joint power research team can naturally understand what he said.

Everyone who was a little tired after staying up all night instantly regained their energy.

The engineer who was the first to notice Chang Haonan's absence showed an expression of enlightenment:

"So point O is the initial unstable operating point of the system. We need to find out the earliest position in the compressor that meets the operating conditions shown at this point. Is it the earliest surge-inducing point where flow separation occurs?"

"That's right, so everyone must find this location as quickly as possible and let the institute do a forced breathing test to see if this problem can be reproduced!"

Yan Zhongcheng threw the pencil on the table next to him and stood up from the chair.

For a moment, he suddenly felt a sense of hypoxia coming from his brain, and at the same time, his vision went black.

This is caused by long-term irregular work and rest, overloaded work, and sudden standing up after sitting for a long time just now.

However, Yan Zhongcheng used one hand behind his back to support the table in time, so it didn't appear too obvious.

In order to divert other people's attention, he forced himself to continue assigning a task:

"Also, I will meet with the comrades over at Institute 601 later and bring the flow data of the air inlet for reference."

"understand!"