Chapter 94: Knowing is not a blessing

When Zhang Donglin saw the experimental data recorded by his junior brother, his first feeling was that he was a little confused.

But after all, he had been studying for a PhD for three years, and he quickly found something valuable in the mess of numbers.

"It's kind of interesting......"

Although, as his junior brother said, the data stability of these sets of experiments he made was very poor.

However, if we ignore the huge variance and only take the average, we can still find that when the Mach number Ma=0.40 and the angle of attack are 0°, 3° and 6°, the corresponding total pressure loss coefficient is reduced by 7.0%, 32.1% and 32.3% respectively, the average airflow turning angle is increased by 4.02°, 3.59° and 1.78°, and the stable operating range is increased by 3.5° angle of attack.

Obviously, this is quite an impressive step forward.

However, the calculation method of "ignoring variance and averaging directly" is obviously not elegant, and Zhang Donglin has to make sure that this result can be reproduced, and not due to some kind of misoperation.

Looking at the experiment notebook in front of him, he took two deep breaths in a row:

"Senior brother, I want to see the process of your experiment just now, can you repeat it as it is?"

"Ah...... Of course, no problem. ”

In the following two hours, Zhang Donglin watched his junior brother repeat the experiment with skillful movements, and at the same time took out a notebook to record some of his thoughts and ideas.

In the case of such exaggerated fluctuations, the experimental results are naturally different from those just now, but the overall law remains the same.

The chord groove that was accidentally opened during the manufacture can indeed improve the performance of the compressor to a considerable extent, especially when working at large intake angles of attack.

Judging from the few sets of data at present, the faster the air intake speed and the larger the angle of attack of the compressor, the more obvious the improvement effect.

In addition, Zhang Donglin also wrote about several factors that may affect performance, such as the location (height) of the opening, the shape and angle of the gap, and so on.

However, before he finished writing the last part, he knew that this problem would be difficult for his small research group to fully understand.

Compared to the tip consistency and accumulation lines that they are now focusing on, there are so many independent variables associated with this slit that it feels a little outrageous.

More importantly, the compressor experimental equipment of Bingcheng University of Technology can only support typical subsonic research with Mach number Ma = 0.59 at most.

With some tangled feelings, Zhang Donglin found his mentor Yu Fei.

"This ...... How is this possible? ”

After seeing the data on the experiment notebook and listening to Zhang Donglin's analysis of it, Yu Fei's first reaction was almost exactly the same as that of his students:

"This kind of tangential slit will lead to the meeting of the small flow velocity turbulence with low total pressure and the main stream with high total pressure, the velocity is added on the vector, the main fluid velocity decreases, and the wake fluid velocity increases, and this process will produce serious mixing losses, how can the total pressure loss coefficient be reduced?"

"In addition, the volatility of this raw data is too large, and I estimate that the correlation coefficient may not even be 0.7, how dare you directly average this kind of data?"

"But I asked my junior brother to repeat this experiment again, and the results still showed the same pattern." Zhang Donglin does not intend to give up this opportunity:

"And you should also take into account that the leaf slit will certainly increase the mixing loss, but at the same time, it can also play a role in blowing out, delaying the large-scale separation of the attached surface layer of the leaf grid in Ye Shan, and there should be a competitive relationship between these two effects!"

“……”

The master and apprentice stared at each other in silence for a few seconds.

As mature researchers, they know that it is impossible to solve the problem here.

Yu Fei supported his chin with one hand, and beat on the table with the other hand almost unconsciously, and thought for a few minutes before he spoke again:

"You know that the flow loss inside the compressor is almost a mystery to us at present, if you want to study this problem from a mechanistic point of view...... I'm afraid it's hard to get an answer. ”

"But if you do the experiment......"

He didn't say it directly, but in fact, even Zhang Donglin knew that the laboratory of Bingcheng University of Technology did not have the ability to do so.

There was silence again in the office.

"In this way, you first design a set of experiments, and do all the parts that can be done in our laboratory, considering that the research in this area is still basically blank, I think if you put in a little more effort, it should not be a problem to publish a journal of aeronautics or aerodynamics."

"But...... The effect of such research should be discounted, and we can't do the part of the supersonic or even high subsonic compressor at all, I think ......"

"I know what you mean,"

Zhang Donglin's words were interrupted by Yu Fei raising his hand before he finished speaking:

"How to deal with the rest of the matter depends on the results you make next, if there is no way to determine below the classic subsonic, then this direction is basically equivalent to being blocked, or return to the original more secure route as soon as possible."

"And if the results of the experiment show that the two of you are not wrong...... This is a major breakthrough in compressor design. ”

Hearing the last few words, Zhang Donglin's eyes lit up:

"A major breakthrough?"

As a doctoral student at Bingcheng University of Technology, he knows the weight of these four words too well.

"But...... Don't rejoice too soon. ”

Yu Fei looked at Zhang Donglin, who seemed to have a fox's tail up, and said:

"As you just said, the hardware conditions on our side are limited, and there is no way to do more in-depth research, so I am ready to report to the Commission of Science, Technology and Industry for National Defense, and let them organize people to conduct a comprehensive evaluation."

"So I just asked you to take advantage of this time to hurry up and do experiments, and form an article to send out first, so that on the one hand, it is possible for you to directly participate in the project of the Commission of Science, Technology and Industry for National Defense, and on the other hand, you can at least leave something for yourself."

"Besides, you're not just one paper away from graduation requirements?"

This last sentence persuaded Zhang Donglin, and he decided to solve the graduation problem in front of him first, and then think about how much more could be dug up from this inadvertent discovery.

As a result, after two months of experiments, submissions and waiting, a paper entitled "Numerical Analysis of Blade Grid Characteristics after Slotting from Pressure Surface to Suction Surface" appeared in the Journal of Aerodynamics.

At about the same time, Yu Fei declared this paper as a key achievement to the direct supervisor of Bingcheng University of Technology, the Commission of Science, Technology and Industry for National Defense, saying that this achievement has the potential for further follow-up research.

Should I say it or not, Zhang Donglin and Yu Fei's efficiency is still a little slower.

If we follow the normal administrative process, this topic will still come full circle to the side of the 606 Institute, but there is a high probability that it will not be able to catch up with the technical improvement of Turbojet 14

Fortunately, Yao Mengna, who finished work one day and went to the library to borrow a book to read, noticed the paper, and was driven by curiosity to borrow it and bring it back to the computer room.

(End of chapter)