Chapter 84 Unstable Working Line
The first and most core step of this task is to find the common working conditions of each component of the turbojet 14 engine and establish a common working equation.
It happens to be the part that Chang Haonan probably knows what 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 complicated, and it is not his best field, 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) The power balance of the compressor and the turbine on the same shaft..."
"(3) The rotational speeds of the compressor and turbine on the same 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 satisfy the balance between the degree of supercharging and the degree of expansion. Conditions..."
"..."
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 gave a response:
[The technology points consumed to perfect the project: 10 points, and the points consumed to directly give the project results: 100 points, Is it confirmed to carry out the unstable operating line calculation project of turbojet 14 engine? 】
"It finally happened..."
Chang Haonan slowly took a deep breath.
"Confirm! Complete the project!"
......
The entire evening 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 non-dimensionalization 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 among 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 defect, a manufacturing defect, 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.
Engine design is of course a matter that affects the whole body, but no matter how complicated the task is, there will always be a starting point.
Just like the thread in a ball of wool.
"Gong Yan, why don't you go and 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 passes, the ins and outs of the surge problem are becoming increasingly clear in Yan Zhongcheng’s mind.
“You all come here.”
He waved his hand behind him and called 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.
“Yes, it seems that I haven’t seen anyone else since last night.”
“Did you run away to rest by yourself?”
“Forget it. Let’s go look for it later, and 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:
"Look, I have separated out the surge oscillation ring separately. The O-A, A-B, B-R and R-O above are 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 O-A, the pressure rise that the compressor can provide cannot balance the pressure buildup in the rear part. Under the action of strong back pressure, the gas flow rate flowing through the compressor drops sharply, but due to the lag of dynamic response, the pressure after the compressor changes slowly in some cases, such as the boost pressure of the compressor. When the flow rate is high, the instantaneous flow rate of the compressor can be reduced to zero, and even reverse flow may occur. "
"When the instantaneous flow rate reaches the minimum value at point A, the corresponding system pressure at the rear of the compressor will flow in through the compressor. The flow rate is much smaller than the flow rate flowing out through the pressure regulating valve, so in the second part of A-B, the flow rate flowing into the compressor continues to increase, while the pressure at 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 approaching the original stall starting point O again from R. "
This work. The biggest difficulty 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 discover that Chang Haonan was not around just now showed an expression of enlightenment:
“So point O is the initial unstable operating point of the system. We need to find out the earliest unstable operating point in the compressor. The position that meets the operating conditions shown at this point is the surge induction point where flow separation occurs first? ”
"That's right, so now we need to find this location as quickly as possible and let the institute do a breathing test to see if this problem can be reproduced!"
Yan Zhongcheng said and threw the pencil to On the table next to him, he stood up from his chair.
For a moment, he suddenly felt a sense of hypoxia coming from his brain, and at the same time, his eyes 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 the attention of others, he forced himself to continue assigning a task:
"In addition, I will meet with the comrades over at Institute 601 later to collect the flow data of the air inlet. Take it for reference too.”
“Understood!”
(End of this chapter)