Chapter 108 Temperature before turbine
At the same time, Yao Mengna was sitting on a chair in the corner of the control room, almost out of everyone's attention.
On the surface, she seemed to be staring at Chang Haonan's side face in a daze.
Well, actually it is.
But the reason for being dazed was not that he was attracted by the latter's appearance and became a nymphomaniac.
But after she witnessed the high-altitude platform test process just now, an inspiration flashed in her mind.
But he didn't have time to catch it.
I just vaguely felt that the inspiration just now was related to my junior brother.
Yao Mengna believes that visual stimulation can stimulate the subconscious mind and remind herself of useful things.
Well, it’s all for scientific research.
In short, when she really captured the inspiration again a few minutes later, she even felt a little disappointed.
Damn it, I can’t find any other excuse to lie to myself...
"Forget it, business matters."
Yao Mengna shook her head slightly and temporarily put aside the messy thoughts in her mind. Then she stood up and walked quietly along the edge of the room to the computer that recorded the test data.
In fact, on the way off the plane, she was thinking about the unstable operating conditions of the turbojet 14 that Chang Haonan had mentioned before.
And now she has an immature but logically self-consistent guess.
Just need some data to confirm.
Soon, she found the inconspicuous project from the vast sea of records——
Combustion chamber outlet temperature/turbine front temperature.
"very good."
With her eyes fixed on the screen, Yao Mengna raised the corners of her mouth slightly and murmured softly.
However, the excitement only lasted for a moment.
After clicking in to check, she found that the data inside was incomplete.
This indicator is very important in the design and manufacturing process of combustion chambers and turbine blades, but is generally not a focus in high-altitude bench testing.
The main reason is that it is really not easy to test.
The accuracy of non-contact measurement is not high, and the technology is not mature enough. The engine even needs to be specially modified for testing.
Contact temperature measurement requires the insertion of armored thermocouples. One or two is not a problem, but if you want to obtain a complete temperature field, there will be many points that need to be measured. A large number of thermocouples themselves will affect the internal flow field of the engine. Produce interference and affect working status.
Therefore, as long as the engine's core indicators such as intake air flow and thrust are normal and there are no problems with the turbine's operating conditions, the temperature in front of the vortex will not be measured frequently.
At most, we can only give the data of 1-2 sampling points like this to ensure that no accidents will occur due to overheating.
But she needed more comprehensive data.
After a few seconds of hesitation, Yao Mengna finally decided to talk to Chang Haonan about the matter first.
With the lessons learned from the last blade slit design, she will not allow the project progress to be delayed again due to her own reasons.
"Junior brother." Yao Mengna bypassed the crowd that had just finished celebrating and came to Chang Haonan:
"I would like to conduct an overall measurement of the temperature field in front of the turbine in the middle of the subsequent air performance test."
"Temperature before turbine?"
Chang Haonan raised his head and glanced at Yao Mengna in front of him, then quickly flipped through the report in his hand, and quickly found the page with the corresponding data.
"The maximum temperature in front of the turbine is 1575K, which does not seem to exceed the design tolerance, and judging from the overall working condition of the engine, it is also..."
Halfway through his words, Chang Haonan suddenly paused.
"Do you think there will be a problem with the temperature distribution in front of the turbine?"
"That's right." Yao Mengna nodded firmly:
"The data obtained now are only the results of sampling at two points at the center and edge of the turbine."
"If it is a generally radially symmetric temperature field, there is certainly no problem with this measurement method, but the turbine blade itself has an active cooling function."
"If the air film formed on the surface of the turbine blade is not uniform enough, the cooling effect will fluctuate. At around 1600K, even a temperature change of only 20-30 degrees will significantly change the physical properties of the blade and affect the overall operating conditions of the engine. stability.”
"..."
Chang Haonan turned to the back of the test report in his hand while listening to Yao Mengna's thoughts.
Sure enough, unstable operating conditions similar to those on the No. 01 and No. 03 prototypes were discovered in the data again.
Fortunately, this time he had reserved enough surge margin, so even during the thrust transient, no malfunction occurred.
However, the sensor still faithfully recorded the dramatic fluctuations in compressor mass flow and boost ratio at the moment the throttle lever state changed.
"I think it is indeed possible..."
Looking at the report in his hand, Chang Haonan realized that he had fallen into a misunderstanding.
Because the position where the operating condition fluctuations were initially recorded was the compressor.
Later, the part he presided over the modification was also the compressor.
So he always felt that the problem lay in this part.
But things like aircraft engines can affect the whole body.
The principle of film cooling is to introduce a secondary air flow from the hole on the wall in a high-temperature environment to the mainstream, allowing this cold air flow to bend downstream under the pressure and friction of the mainstream, and adhere to a certain area of the wall, forming a lower temperature The cold air film isolates the wall from the high-temperature gas and takes away part of the radiant heat from the high-temperature gas to the wall of the part, thereby cooling and protecting the wall.
This process requires the extraction of low-temperature air from the compressor as a cooling fluid, which will directly affect the air flow inside the compressor.
Of course Chang Haonan knew the principle, but after all, it was not his previous profession, so he didn't think of it for a while.
"Thank you for reminding me, senior sister."
Chang Haonan quickly packed up the reports on the table and prepared to go outside to find Yan Zhongcheng.
During the entire bench test, he was only responsible for the intake distortion test related to compressor improvement. The person in charge of other test subjects was still Yan Zhongcheng himself, so if the test items were to be temporarily added, the latter's signature would be required.
"It's okay, as long as I can help."
Yao Mengna originally wanted to hug the other person, but after thinking about it, it seemed that it was not the right time, so she had to put down her half-raised arm.
"It would be nice if I came here when the test results just came out..."
Fortunately, at this time, Yan Zhongcheng, who had just left the control room, pushed the door back in without letting Chang Haonan notice her embarrassed expression.
"Mr. Yan, regarding the air performance test that will be conducted later, senior sister has come up with an idea..."
……
With Chang Haonan's current ability, this suggestion was naturally passed very smoothly.
In 1996, there was no very reliable non-contact online measurement method, so the staff of the 624th Institute installed a batch of armored thermocouples on the high-pressure turbine guide overnight.
After the three-hour experiment, the raw data was quickly given to Chang Haonan.
The subsequent analysis results proved that Yao Mengna's previous guess was completely correct.
Under the maximum afterburner thrust, the engine turbine inlet temperature field is distributed parabolically along the blade height, that is, the temperature at the blade tip and root is low and the temperature at the middle position is high, which is consistent with the design law.
However, as the engine speed gradually decreases, the unevenness of the temperature field in front of the turbine begins to increase.
The unevenness reaches its highest level when the throttle lever is near the "minimum afterburner" position.
This is exactly the same as what was recorded during the testing of the two prototypes - the most severe fluctuations in operating conditions occurred during transonic acceleration or deceleration.
Right!
