Chapter 416 Choice, 10 technical routes for turbofans
“The core engine of GE9 is good everywhere, but the total pressure ratio is too high, and the low aspect ratio compressor blades are not suitable for us regardless of design. Manufacturing or manufacturing is a completely new topic. Now that we have the successful experience of the turbojet 14, there is no need to start a new business in this kind of place..."
Chang Haonan quickly wrote down a few words on the paper while introducing it. String of numbers:
“There are currently several mainstream third-generation high-thrust turbofan engines in the world. The pressure ratios of F100 and AL31F are in the range of 24-25. The pressure ratio of F110 is outstanding, and it should be nearly 31. I see that your design even uses a more efficient curved blade design for the compressor. I am afraid that the pressure ratio will go to 32-33, which is suitable for the two installation targets of our turbofan 10. The installation performance will be very poor..."
After all, the aviation engine cannot stay on the ground test bench all the time, but must be installed on the aircraft and actually take off for flight.
Therefore, even if the aviation power system becomes independent in the future and the engine project no longer exists as a supporting component of the aircraft project, it is impossible to design the aviation engine without considering the actual situation of the aircraft to be installed.
High pressure ratio is indeed a good thing, but it is definitely not that higher is better without thinking.
For engines with excessive high pressure ratios, especially turbofan engines, after exceeding the speed of sound, the power consumption of the compressor will increase rapidly, causing the isentropic compression line to shift to the right, the compressor efficiency will decrease, and the cycle work will decrease.
Although the total pressure ratio on paper is still very high, the actual available effective pressure ratio is lower.
In terms of actual performance, the engine is one-stop at medium and low speeds, and turns into a worm at high speeds.
Both F110 and F404/414 have this problem.
How big is the gap?
These two engines, which are obviously more advanced in technology, not only have a thrust curve inferior to the AL31F and RD93 at supersonic speeds, but their fuel consumption performance is also inferior to the latter two.
This is a problem limited by basic physical principles.
Unless a variable cycle engine is developed, it is impossible to achieve a balance of performance under various working conditions from the root.
The F119 engine on the F22 chose a design completely opposite to that of the F110 for supersonic performance. The result is that it can cruise at supersonic speeds without using afterburner, but the fuel consumption in military push mode is extremely high, resulting in a huge amount of fuel in the entire aircraft. Instead, it turned into a short leg.
It’s not that Puhui’s designers are incompetent.
It’s just a choice.
The ATF project was born at the height of the Cold War. The combat scenario at that time was to conduct a short, high-intensity battle over Europe, and then either be shot down or return, which did not require a long voyage.
It’s just that the plan couldn’t keep up with the changes. When the F22 entered service in 2005, it was discovered that it had to go to the vast Pacific region to use its waste heat. As a result, the performance was out of touch with the needs.
Of course, although it is impossible to fundamentally solve the problem, there are still ways to improve it -
Just redesign the aircraft with an adjustable inlet that has a better match and a wider range of boost capacity adjustment. .
The later new model F15 adopted this idea.
As for the F16 and F18...
Laughing to death, what kind of supersonic performance does a medium-sized aircraft need? Just stay put.
The current situation is that the overall design of the J-11 is that of the Su-27. The basic design of the fuselage + air intake already has an incredible boost capability. It is not easy to lower it.
The J-10 has simply decided to use a non-adjustable DSI inlet. It is also impossible to fix the inlet state in a low-efficiency and low-boost-ratio state.
So although the turbofan 10 can be freely used at the specific technical level, in terms of performance and style, it still has to follow the F100/AL31F route, and it is appropriate to set the boost ratio around 25.
The overall design of aeroengine is an extremely complex system engineering, which has been reflected before the real "design" work begins.
“Oh...”
After Chang Haonan's explanation was over, Hai Yide and Liu Yongquan stared at each other for a few times.
We are all professional and technical personnel. Although we were inexperienced and did not think of this level before, now that others have said it, we can still understand it.
"But Mr. Chang, if the boost ratio is limited, the overall performance of this engine at subsonic speeds, especially the fuel consumption and thrust-to-weight ratio, will definitely be affected..."
The main performance optimization range of third-generation fighter jets is definitely between high subsonic speed and transonic speed.
Whether F100, AL31F or RD93, they all sacrifice a certain degree of subsonic performance, especially the RD93. The huge fuel consumption at low speed (still dual engines) plus the small internal oil directly gives rice Box 29 brings the title of airport defender.
This is indeed a critical issue for the Chinese Air Force, which is expected to conduct high-intensity operations far away from the airport.
“Yes, Mr. Chang, the J-11 has 9 tons of internal fuel. I don’t care about the fuel consumption, but I look at the body of the J-10, and the internal fuel capacity should not be very optimistic...”
Hai Yide, who was next to him, also expressed the same concerns.
In fact, this is one of the main reasons why 611 directly tied the two inner pylons to the auxiliary fuel tank when it first designed the J-10.
AL31FN is still AL31F after all. It just changed some minor details such as the position of the accessory box. The engine is still the same engine.
After being installed on the J-10, the range without auxiliary fuel tanks is really not impressive. However, Chang Haonan shook his head decisively:
“The problem of fuel consumption can be solved by increasing the temperature in front of the turbine by 50-100°C.”
This is Quite a simple and crude method, but also the most effective.
Chang Haonan adopted the same approach on the turbojet 14 to ensure that the performance of the J-8C at different altitudes and speed ranges is balanced.
"Mr. Chang, the temperature in front of the turbine that we are promoting in the third generation is now set at around 1200°C. This is already a high threshold for our material science level. If we increase it further..."
As an aviation engine designer, Liu Yongquan has naturally considered these issues comprehensively, but looking at Chang Haonan who was holding a pen next to him without raising his head, and then thinking about what happened on the Turbojet 14, it doesn’t seem that incredible.
However, after hesitating for a while, he still said:
"If we add more, I'm worried that the risk level and progress of the entire project will be out of control."
1200 ℃, has become the mainstream level of the international third-generation turbofan engine.
It is indeed difficult to produce turbine discs and turbine blades with heat-resistant levels that surpass those of the United States in a short period of time.
With materials science, there is little opportunity for opportunism.
China can now produce nickel-based high-temperature alloy raw materials with similar performance to ReneN5, but it still has the same old problem. If you want to build something, just having a piece of raw material is of no use. For every material They also require a series of supporting research such as subsequent processing, which are also quite time-consuming and resource-consuming.
If we give up the second-generation alloy materials that we already have some supporting research results and industrial practical experience in hand, and jump directly to the third-generation, then the risks involved will be very difficult to say.
“Of course it is too radical to change materials directly...”
After directly using system points to smash TORCH Multiphysics, Chang Haonan is now on the verge of "bankruptcy" and does not have so many points to use to comprehensively improve the level of the entire field of materials science.
This method of improvement is too rigid and does not conform to the logic Chang Haonan set at the beginning.
Taking a step back, even if there is help from the system and everything goes smoothly in the middle, it will take at least several years for him to solve the numerous problems in the middle by himself.
Chang Haonan’s plan is to try his best to give at least the prototype aircraft equipped with the turbofan 10 the opportunity to participate in the 50th anniversary National Day military parade in more than two years.
It will definitely be too late to wait for the materials.
"So I plan to use a new active cooling solution on the turbine structure. The current film hole cooling still has great potential. Without changing the base material, it is not a big problem to increase the temperature in front of the vortex by 50-100°C. "
After finishing speaking, he ignored the stunned people beside him and took the simple diagram in front of him again:
"As for the thrust-to-weight ratio you just mentioned. Question, let’s just give up the 3-9-1-2 structure, or rather this structure.”
“Huh?”
The other people in the conference room only thought of themselves. The brain is on the verge of death because it has received too much information in a short period of time:
"If we don't use this structure...should we use a centrifugal compressor?"
The turbine compressor of the turbine can be simply divided into centrifugal type and axial flow type according to the principle. Generally speaking, except for the early ones, Outside of this stage, most turbojet/turbofan engines have uniformly used axial flow, and only some turboprop/turboshaft engines will adopt centrifugal designs.
"Of course not..."
Chang Haonan was a little helpless:
"What I mean is to use a more efficient single-stage load to reduce the number of compressor stages. , compress the three-stage fan into a 1-stage or 2-stage fan, and the 9-stage high-pressure compressor into a 6-stage or 7-stage fan. Considering that the entire compression system accounts for about 60% of the weight of an engine, if it can be used here If the weight of the engine is reduced by 20%, the thrust-to-weight ratio of the entire engine can be increased by at least 10%.”
"Do you still remember the 'ultra-high-load adsorption-type curved and swept combined leading edge edge blade' that I took out as an example during the last meeting?"
Haiyide didn't do it last time Went to a meeting, but Liu Yongquan went there.
Also listened very carefully.
So he was the first to react from his confusion and nodded:
"Remember, I also took notes..."
As he spoke, he took out a notebook from the bag he carried with him and opened it to one of the pages.
From the slightly worn traces, it can be seen that he probably read a lot during this time.
“That’s good.”
Chang Haonan lightly tapped the title on the notebook with his finger:
“This thing is from our compressor design part. Core technology.”
"The leaf-shaped design you have learned before, whether it is end bending or end sweeping, end wall shape, or edge strips, is still a means of passively controlling flow separation."
"The reason why I want to When it comes to adsorption blades, it is necessary to use active control methods to further increase the single-stage pressure ratio, so that each stage can exert the compression effect of one and a half to two stages in the past! ”
(This chapter! End)