Chapter 511: Turbofan 9A preparing to tap its ultimate potential

Chang Haonan certainly didn't mean to look down on Teacher Yang Huimei.

But to be honest, the subject of management itself is more practical than theoretical.

There is really no need to take the paper too seriously.

For a management professor, being able to arrange jobs for all his graduate students is a reflection of his ability...

In short, after sending Xu Yang and Yang Huimei away, Chang Haonan finally took care of the first thing of the day.

It also settled a minor worry.

The paper itself is of course of little use to Chang Haonan, but he is somewhat looking forward to the impact it may have on the Torch Group and even the entire Chinese academic community.

There are two other emails left in the mailbox.

The content of the second email was much more ordinary in comparison.

It was Liu Hongbo, who had already started working in Bingcheng, asking whether the technical ideas for helicopter sound field simulation were feasible——

“Currently, the calculation of helicopter rotor noise basically uses the Lighthill acoustic analogy method based on the FW-H equation.”

"After several days of trying, I found that this method performs well in calculating rotor thickness and load noise, but it cannot be used to solve the nonlinear noise of the quadrupole source, resulting in abnormally high noise during the helicopter's hovering/forward flight process. …”

"And if the experimental method is completely used, on the one hand, the 122nd Factory and the 602nd Institute do not have enough acoustic laboratories for helicopters, and on the other hand, the cost and development cycle cannot be guaranteed..."

"I'm trying to get results by calculating the flow field first, and then determining the rotor vibration through the flow field, thereby indirectly calculating the sound field, but there are some issues that need Mr. Chang's guidance..."

"..."

Chang Haonan gathered his thoughts and began to think about the content of the email.

It should be said that the depth of research conducted by Bingfei Group was higher than he had previously expected.

The so-called quadrupole source nonlinear noise is medium-high speed impulse noise (HSI).

When the rotor speed is high, shock waves may exist on the surface of the rotor blades and extend to the spatial area. The flow field exhibits transonic and strongly nonlinear characteristics, and will emit very penetrating and discernible pulses. sound.

For helicopters, the impact of noise is not just a matter of comfort.

Sound = vibration.

Since lift is mainly obtained by the rotor, this type of HSI noise may not only cause hearing damage to the members in the aircraft, but also cause unstable factors such as rotor tip flutter, affecting flight safety.

For military helicopters, excessively loud and easily identifiable sounds can also lead to easy early detection.

Helicopters are slow and have poor maneuverability. The core of their survivability is the concealment brought by the height of the treetops. If they are discovered a few kilometers in advance, it will greatly increase the risk of being attacked by concentrated fire.

However, in the current 90s, research on "quiet rotors" in various countries is generally still in its infancy.

Although models such as the Mi-28 and AH64 have tried to use some qualitatively effective technologies, overall, noise still ranks relatively low in everyone's performance requirements for helicopters.

Just don't go too far.

Generally speaking, the best way to suppress HSI is to increase the rotor diameter/number of blades and reduce the linear speed outside the blades.

The trade-off is increased weight and complexity of the rotor.

As for helicopters like the Z-9, which are already in short supply of power, and the 122 Factory, whose technological level is far behind that of European originals, obviously they do not have the conditions for this...

After thinking about it, Chang Haonan took out a few sheets of A4 paper from the printer tray next to him.

Anyone who has ever done this kind of thing like writing formulas on a computer knows how frustrating it can be.

Immediately afterwards, while sorting out the calculation ideas that emerged in his mind, he began to write furiously:

"The FW-H equation has shortcomings in the universality of the research problem. The essence and premise of accurately calculating the rotor sound field is to calculate the rotor flow field. As long as the shock waves and tip vortices that may exist in the flow field can be captured through calculation, acoustics It is not difficult to ensure the accuracy of the calculation..."

"Specifically, you can try to obtain the far-field sound pressure characteristics by integrating the sound pressure value on the surface surrounding all sound sources. The sound pressure value on the surface can be determined by Kirchhoff's formula..."

"In actual numerical calculations, the integration surface must be discretized into small surface elements. The integration is performed on each surface element. The final result is the superposition of the contributions of each surface element. dS is the area of ​​the micro-surface element..."

"The information obtained from the flow field calculation can be calculated on the Kirchhoff surface through interpolation and other methods. For the unstructured overlapping grid of the new version of TORCH Multiphysics, a method similar to the hole boundary generation in the nested grid can be considered. method to determine the integral surface..."

"Artificially given a space surrounding the blade, which is similar to a "hole" in a nested grid, first loop through all the grid points and determine whether the point falls within the hole according to the spatial coordinates. If the point falls within the hole , then mark the point as 0, otherwise it is 1..."

"..."

"As for flow field calculation, the essence is back to the numerical solution of NS equations. This is the core function when the TORCH Multiphysics software was created, and I will not go into details here..."

"This is my understanding of the above-mentioned issues. It is a personal opinion and is for reference only."

"And I wish you success in your project."

The five pages of A4 paper were written eloquently and quickly.

After briefly checking that the contents were correct, Chang Haonan put several pages into the scanner.

The paper-fed scanner was invented in the early 90s and has now entered the Chinese market.

Although the price is ridiculously high, Chang Haonan is not too poor with money after all, so he still gritted his teeth and equipped each office with one.

After scanning it in, he directly sent the content as an attachment to Liu Hongbo in Bingcheng.

After handling the two things without incident, Chang Haonan looked at the clock on the wall.

It's almost time to have lunch.

He clicked on the last unread email.

This is a routine work report for the Turbofan 10 project.

One will be sent every few days.

After a brief look at it, he planned to go and have lunch.

however.

"Experimental results of flow heat transfer characteristics of special-shaped air film holes"——

When he saw this title, Chang Haonan knew that he would not be able to eat his lunch.

This research is crucial for the design of combustion chamber and turbine structures of aeroengines.

He has previously used the basic control equation of flow heat transfer to calculate the film cooling effect of different shaped holes.

But after all, this is a research direction that has never been done before, and experimental results are still needed to correct the numerical calculation method.

That's why it has been postponed until today.

Thinking of this, he couldn't sit still anymore, quickly turned off the computer and put on his coat, ready to see the results.

There is so much experimental data from more than a month ago that there is definitely no way to send it all via email.

……

Inside the Compressor Research Center of Beijing Hang University, Liu Yongquan, wearing a blue lab coat, stood in front of two computers recording experimental data.

Next to him was Chang Haonan, who was concentrating on checking the experimental data and comparing it with his own calculation results.

"Judging from the results, for our experimental subjects, the cooling effect of dustpan-shaped holes is better than fan-shaped holes and simple forward-inclined holes. However, the influence of expansion ratio, hole inclination angle and expansion angle on cooling efficiency is still relatively complicated. …”

Chang Haonan stared at the two screens at the same time and slowly gave his judgment.

"Actually, the key is that we do not have the means to directly measure the velocity and pressure distribution in the air film holes. On the one hand, we cannot buy the relevant sensors, and on the other hand, even if they are obtained through special channels, the accuracy cannot meet the requirements..."

Liu Yongquan said from the side, obviously still a little regretful.

"When we engage in scientific research in China, we have never reached a stage where we get what we ask for."

Chang Haonan didn't care too much:

"The velocity and pressure distribution in the hole are the cause, and the displayed temperature field distribution is the effect. If the theoretical tools are advanced enough, even if the former cannot be obtained directly, it can be inferred from the results."

Liu Yongquan opened his mouth, but was so shocked by Chang Haonan's confident words that he had nothing to say for a moment.

After a while, he spoke again:

"Under different environments, the heat dissipation effects of various hole types will be somewhat different."

"For this part, testing in a laboratory environment alone is not very useful. Actual testing is still needed to prove the feasibility of our design."

Chang Haonan was certainly prepared for this kind of thing:

"That's no problem. I'll contact Liming Factory this afternoon and ask them to prepare to apply the new cooling technology on the second-stage prototype of the turbofan 9A."

"Wolffan 9A?"

Liu Yongquan was stunned:

"But the temperature in front of the turbine of Turbofan 9 is a bit too low for our technology, and no effect can be measured..."

"Just modify the atomization level of the fuel injection structure and increase the temperature of the combustion chamber."

Chang Haonan raised his head and said:

"Although the foundation of Turbofan 9 is average, the value of continuing to tap the potential will not be too great, but we are just changing the design without changing the process and materials, and the cost will not increase too much."

"The temperature in front of the turbine of the improved model is increased, which can at least improve some supersonic performance and reduce some additional fuel consumption."

Seeing what he said, Liu Yongquan naturally had no objection.

"Mr. Chang, you are trying to squeeze out all the potential of Sibei..."

There was a hint of compliment in the words.

"It's best to make the best use of everything. There are so many troops in the Air Force waiting to be replaced. It will also be a big help to get the JH-7A out early..."