Chapter 511 Turbofan 9A preparing to tap its ultimate potential
Of course Chang Haonan did not 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.
Professor of management, 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.
Forget it and settle a minor worry.
Of course the paper itself will have little effect on Chang Haonan, but the impact it may have on the Torch Group and even the entire Chinese academic community still makes him look forward to it.
There are two other emails left in the mailbox.
The content of the second email is 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 Lighthill acoustics based on the FW-H equation. Analogy method. ”
“After several days of trying, I found that this method performed well in the calculation of rotor thickness and load noise, but it could not be used to solve the nonlinear noise of the quadrupole source, causing the helicopter to hang. The noise during parking/forward flight is abnormally high..."
"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, on the other hand, the cost and R&D The period cannot be guaranteed..."
"I am trying to calculate the sound field indirectly by first calculating the flow field, and then determining the rotor vibration through the flow field to get the results, but there are some issues that need Mr. Chang's advice. …”
"..."
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 and 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 Pulsating tones with power and distinction.
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 make it easy to be detected in advance.
The helicopter is slow and has poor maneuverability. The core of its survivability is the concealment brought by the height of the treetops. If it is discovered several kilometers in advance, it will greatly increase the risk of being attacked by concentrated fire.
However, in the current 1990s, research on "quiet rotors" in various countries is generally still in its infancy.
Although Mi-28, AH64 and other models have tried to use some qualitatively effective technologies, in general, noise still ranks relatively low in everyone’s performance requirements for helicopters.
Just don’t be too outrageous.
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, combined with the fact that the 122 Factory, whose technological level is far behind European original products, obviously does not have the conditions for this...
After thinking about it, Chang Haonan Still pulled out a few sheets of A4 paper from the printer tray next to it.
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 and is not accurate. The essence and premise of calculating the rotor acoustic field is to calculate the rotor flow field. As long as the shock waves and blade tip vortices that may exist in the flow field can be captured through calculation, the accuracy of the acoustic calculation is not difficult to ensure..."
"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..."< br>
“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 TORCMultiphysics, a method similar to the nested grid can be considered Hole boundary generation method to determine the integration surface..."
"Artificially give a space surrounding the blade, which is similar to the "hole" in the nested grid, first loop through all the grid points , judge whether the point falls in the hole according to the spatial coordinates. If the point falls in the hole, mark the point as 0, otherwise it will be 1..."
"..."
"As for the flow field calculation, the essence is back to the numerical solution of the N-S equation. This is the core function when the TORCMultiphysics software was created, and I will not go into details here..."
"This is my answer to the above problem. Understood, this is just for reference. ”
“And I wish you a smooth completion of the project. ”
The five pages of A4 paper were written quickly.
After briefly checking that the content just now was correct, Chang Haonan put several pages into the scanner.
The paper-fed scanner was invented in the early 1990s 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 got one for every office. 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 on the turbofan 10 project.
The kind that will be sent to you every few days.
After he planned to read it briefly, he went to eat his 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 the combustion chamber and turbine structure 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. He quickly turned off the computer and put on his coat, ready to see the results.
The experimental data for more than a month is so vast that there is definitely no way to send it all via email.
……
In 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.
“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 expansion ratio, hole inclination angle and exhibition expansion angle have important effects on the cooling efficiency. The law of influence is still quite 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 is not 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 the stage where we get what we ask for."
Chang Haonan doesn't care much:
"The velocity and pressure distribution in the hole are caused by the The temperature field distribution is the result. 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 and was surprised by Chang Haonan's confident words. There was nothing to say for a while.
After a while, he spoke again:
"Under different environments, the heat dissipation effects of various hole types will be somewhat different."
"This part of the content is not very useful just in a laboratory environment, and actual testing is still needed. , proving the feasibility of our design.”
Chang Haonan has certainly been prepared for this kind of thing:
“This is no problem. I will contact Liming Factory in the afternoon and let them work on the turbofan. New cooling technology is ready to be applied to the second-stage prototype of 9A. ”
“Whipfan 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...”
“Modify the fuel injection structure To reduce the atomization level, just increase the combustion chamber temperature."
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, there is no need to change 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 objections.
"Mr. Chang, you are trying to squeeze out all the potential of Sibei..."
There was a hint of compliment in his words.
“It’s best to make the best use of everything. Now there are so many units in the Air Force waiting to be replaced. It will also be a big help to get the JH-7A out early...”
(End of this chapter)