National Top Stream

Chapter 308 Model Problems

Looking at Zhuang Weiran's calm expression, to be honest, most people couldn't figure out what Zhuang Weiran was thinking.

Sitting in the seat, the representative of the Chinese Academy of Sciences stepped forward and said, "Okay, since everyone has arrived, our meeting will officially begin. Our topic is very simple, and it is about Professor Zhuang's plan."

"Speak freely, don't have any emotions, just discuss the matter."

Professor Qian stood up first and said, "Let me talk about the part we are responsible for first."

"Professor Zhuang's turbulence experiment is very well conceived, and even the mathematical model is very well done. We must admit that no one can surpass Professor Zhuang in terms of nonlinear partial differential equations." Professor Qian paused when he said this , "However, in fact, we agree with the experiment of calculating turbulence, but some of the theoretical aspects that Professor Zhuang withdrew have not been applied to the actual content. To be honest, we cannot accept it."

"Also, I also took a look at the part about computational materials science, which is hard for me to accept, but I still hope that experts in materials science can give me advice on related aspects. I only talk about turbulent flow and computational aspects. It is undeniable that Zhuang Weiran has done a very good job, and it is also very good. But obviously, we cannot achieve perfect data, and we will not be able to achieve it within 200 years. I don’t know what the significance of doing this is. , Professor Zhuang, can you tell me?"

After Professor Qian sat down, Professor Ji stood up and said, "Let me add that we were supposed to use the sart-allaras model, but Professor Zhuang used the rngk-e model and the seven-equation model. To be honest, this The equations are too complicated, if there is any error, it is possible to make the whole experiment and the whole project go to waste.”

"Of course I know that it may be better to use the rngk-e model than the sart-allaras model, but in fact, if we really want to use the rngk-e model, it will not necessarily be better, and it may make the situation worse and worse. Can not control."

"Professor Zhuang." The representative of the Chinese Academy of Sciences looked at Zhuang Weiran and said with a smile, "Do you have anything to say about the doubts of the two professors?"

Zhuang Weiran stood up slowly, not annoyed, and said with a gentle smile, "I personally understand the anger of the two professors, or why the two professors disagree with me."

"In fact, I think everyone here should know that the turbulence model in the aviation field should use the sart-allaras model, mainly wall-bounded (wall-bounded) flow, and it has shown good results. In turbomachinery The application in turbulent flow model is also more extensive.Using bosesq approximation in turbulence model, the central problem is how to calculate the eddy viscosity. The sart-allaras model is a relatively simple single equation model, only need to solve the transport equation of turbulent viscosity, do not need to solve the local shear The length scale of the slice thickness; since the change of the length scale is not considered, it is not suitable for some flow problems with relatively large flow scale changes; such as the flat jet problem, from the sudden change of the flow affected by the wall to the free shear flow, the flow field Scale changes are obvious. However, the gradient of the transport variable in the sart-allaras model near the wall is smaller than that in the ke, which makes the model less sensitive to numerical errors caused by mesh roughness. The sart-allaras model cannot It is asserted that it applies to all complex engineering fluids. For example it cannot be relied upon to predict uniform decay, isotropic turbulence. 1”

"So I chose the rngk-e model, which is more improved than the ke model." Zhuang Weiran said softly, "The rngk-e model comes from strict statistical techniques. It is very similar to the standard ke model, but has the following improvements: 1. rng The model adds a condition to the e equation, which effectively improves the accuracy. 2. Considering the turbulent vortex, the accuracy in this area is improved. 3. The rng theory provides an analytical formula for the turbulent randtl number, while the standard ke model uses is a constant provided by the user. 4. The standard ke model is a model with a high Reynolds number, and the rng theory provides an analytical formula considering the flow viscosity at a low Reynolds number. The role of these formulas depends on the correct treatment of the near-wall region. These features make the rngk-e model more reliable and accurate than the standard ke model over a wider range of flows.2”

"Do you have any doubts?"

"Very good." Professor Qian nodded slightly, and said expressionlessly, "Professor Zhuang chose the rngk-e model, I have nothing to say, but I still want to choose the sart-allaras model."

Zhuang Weiran smiled slightly, "Then why not make two models together?"

"It's going to take a lot of time, so what if the sart-allaras model doesn't work?"

Professor Qian said tit-for-tat, "Does Professor Zhuang think the rngk-e model will definitely work?"

"I'm not sure." Zhuang Weiran said with a smile, "So I personally suggest that the two models should be made together. My plan is also very clear about this aspect. You can take a closer look."

"..." Professor Qian didn't speak, and Professor Ji murmured beside him, "But Professor Zhuang, have you ever thought about the issue of time?"

"I think the problem of time is easy to solve, but what we need to do is not only to hurry up, but also to make this project perfect. We spend so much money and time, if we can't achieve perfection , I don’t think this project is necessary. Sorry, I’m just being so direct.”

"Academician Zhuang." The people in the army said deeply, "I don't understand your research, but I want to ask, how long do you think this research and development will take, and how much money is expected to be invested in the follow-up? What we need to master, as for the rest, we cannot disturb your arguments."

"Within two to three years."

"how is this possible……"

"No way……"

"Academician Zhuang is exaggerating a bit."

"Such a short time?"

The time required for research and development is generally five years or more, and it may even take more than ten years.When Zhuang Weiran suddenly said two or three years ago, everyone was stunned, how could it be possible!For such a large project, it took two or three years to complete it from scratch. No matter how you calculate it, it is considered impossible.

"Professor Zhuang, this joke is not funny at all." Apparently, the people in the army did not believe that Zhuang Weiran would finish it so soon, and they wondered what was the point of Zhuang Weiran making such a joke on such a serious occasion ?

Even for the man who has been hailed as the Pope of Mathematics, a joke on such a serious occasion would turn many people off.

"I'm not joking." Zhuang Weiran said seriously, "Perhaps everyone hasn't noticed the last page behind my plan. I have calculated all the time and engineering, and it is estimated that the entire project will be completed within two to three years."

"About the part of computational materials science, I know that there are many controversies in this area, but it doesn't matter." Zhuang Weiran outlined a smile, "I still suggest that I preside over computational materials science. If other materials science experts disagree, you can Do it according to the previous method, let's see who will do it first, shall we?"

"Professor Zhuang." The person in the army said seriously, "We gathered everyone together to do one thing, not to let you each take over the mountain and become king."

"Professor Zhuang, by doing this, isn't it equivalent to making the whole project more difficult?"

"No." Zhuang Weiran shook his head and said, "I don't need too many people, besides, only the research part needs to be divided into people for research, and the engineering part, I believe no one will separate people for engineering, right?"

"If you both produce results at the same time, the progress of engineering will actually be much slower."

"How about this." Zhuang Weiran said in a deep voice, "If both of us produce results at the same time, how about the results of making the sart-allaras model first?"

"you sure?"

"I'm sure." Zhuang Weiran said loudly, "I know, I'm sure I won't be able to convince any of you today, whether it's the rngk-e model or computational materials science, many people will object, so I don't intend to convince any of you today. But don’t forget, this step is what we must take. If we don’t take it now, I’m afraid it will be even more difficult in the future. I may fail. As long as there is one success among countless failures, this success can grow into a towering big tree."

"I don't regret my choice now."

No one spoke. In fact, they all felt that what Zhuang Weiran said was right, but they had no choice but to be on the safe side.They need to be more stable, Zhuang Weiran's plan has too many unknowns, too many elusive things.

"Professor Zhuang, you probably still need to be the general manager temporarily, but since the two parties have chosen differently, maybe your laboratory needs to be changed."

"I have no problem." Zhuang Weiran said with a smile, "After this meeting, let's see how many people follow me to do the experiment."

The person from the Chinese Academy of Sciences smiled and said nothing, and the people in the army are still struggling with the two-year problem.

"Do you have any questions to ask?"

Everyone, look at me and I look at you, shaking their heads to tell the truth, they don't know what to say.

Basically, the two most important problems have been solved. Although this solution is a bit embarrassing, it has been solved anyway.They didn't speak, they looked at Zhuang Weiran silently.

"Okay, since everyone has nothing to say." The representative of the Chinese Academy of Sciences said, "Then let's end the meeting first. The staff of the turbulence laboratory will have a small meeting in the small conference room later."

"Academician Zhuang." The troops called to stop Zhuang Weiran.

"Is there something wrong?" Zhuang Weiran turned around and smiled.

"You just said that the concept will be released within two or three years or will it be a model?"

"A complete new fighter plane." Zhuang Weiran said with a smile, "Officer, don't worry, I will definitely not let you down."

After speaking, Zhuang Weiran turned and left.The officer muttered to himself, "Academician Zhuang, is he joking?"

When we came to the small meeting room, almost all the personnel in the turbulence laboratory were there.No one spoke, so when he opened the door, Zhuang Weiran said bluntly, "Professor Qian, shall we just say so?"

"Let's talk about it directly." Professor Qian said thoughtfully, "Anyway, it's just a question of the model."