Chapter 471 The key to the next generation of aviation engines

A fifth-generation engine is certainly not possible at the moment.

The third generation is models such as F110 and AL31F, which have a push ratio of about 8.

The fourth generation is models such as F119, F135, and AL51F, which have a push ratio of more than 10.

If the Turbofan 10 is built according to Chang Haonan's ideas, it will probably skip the fundamentalist third generation and directly enter the third and a half generation category.

Of course, there are actually many differences between the third-generation and fourth-generation engines. It can be said that there are differences in the original design ideas, manufacturing processes, and material selection.

The thrust-to-weight ratio is just the most intuitive data that is ultimately reflected in performance.

Of course, there is also a third and a half generation in between, that is, the later models of F110, F414, and AL41F are basically third-generation engines, but they have applied some fourth-generation engine technologies, resulting in performance that is significantly higher than the upgraded versions of their predecessors. .

It is worth mentioning that the fourth-generation engine is no different from the third-generation engine in its most basic principles, so there is still a performance trade-off that is physically unavoidable - high-speed oriented models generally have astonishing fuel consumption, while low-speed oriented models The supersonic performance of the model will be extremely stretched (see Chapter 415 for detailed explanation).

It is precisely to resolve this contradiction that the adaptive variable cycle mode is generally introduced in the conceptual design of fifth-generation engines in various countries.

At low speeds, it can be a fuel-efficient medium-bypass ratio turbofan engine, and at high speeds, it can even transform into a high-performance turbojet engine.

Therefore, although the fifth-generation engine may not be able to achieve such a terrifying leap from 8 to 10 on paper data, it may even be due to the addition of a variable circulation device, causing the sea level thrust-to-weight ratio to fall instead of rising (the dead weight becomes larger) , the thrust has not increased that much), but the actual performance installed on the aircraft will far exceed that of the fourth generation.

However, although the idea of ​​variable loop is simple, if you really want to implement it, there are still too many details to be perfected.

Even until the time before Chang Haonan was reborn, no one had yet determined which cycle-changing technology path was more feasible.

Among other things, the specific design concept of the compressor will undergo an almost earth-shaking change.

So after briefly chatting about the future planning of domestic engine models, Chang Haonan and Liu Yongquan returned to the current research.

"Multiple rows of superimposed full-coverage air film cooling..."

Liu Yongquan repeated this somewhat awkward term.

"Yes."

Chang Haonan took Liu Yongquan to the experimental table next to him. A laptop was placed on it, and an isotherm curve was displayed on the screen:

"I originally thought that the current TORCH Multiphysics software could directly complete the gas-heat coupling simulation, but when I actually operated it, I found that I still thought the situation was too simple."

He said and circled a part of the graph with the brush tool:

"You see, after the main stream comes into contact with the high-momentum cooling jet, a pair of vortex structures with opposite rotation directions will be generated on both sides of the downstream area of ​​the jet. This will play a role in gathering the wall cooling air to suppress lateral diffusion in the direction of rotation of the vortex structure. , and it also has a tendency to lift the cooling air away from the wall."

"so……"

Liu Yongquan still understood this picture:

"So the greater the blowing ratio (the momentum of the cooling airflow), the harder it is for the mainstream to suppress the cooling jet, and the earlier the cooling air will leave the solid wall surface, resulting in a worse cooling effect downstream?"

Chang Haonan nodded, saying that he was indeed the person who really brought Turbofan 10 to maturity in the original timeline. Although he is currently a little inexperienced except for the big hair style, his basic skills are indeed good. He just watched In just a few glances, I quickly grasped the key conclusion:

"That's right, so if you comprehensively consider the gas-heat coupling effect of the entire engine, you will find that if you blindly increase the amount of cooling gas, the improvement in cooling effect will become less obvious as you go further, and it will soon hit an upper limit. And because the airflow loss is too large, it will also affect the performance of the engine itself and even its working stability."

“This is impossible to discover if we only study the film cooling effect on the blades without taking the overall engineering considerations into consideration. I speculate that this should be one of the reasons why the Americans are currently taking a detour. "

After his judgment was confirmed by Chang Haonan, Liu Yongquan almost subconsciously thought of the most direct way:

"If we enlarge the diameter of the air film hole, we can reduce the air flow rate while keeping the amount of cooling air unchanged, and improve..."

But he quickly denied it himself:

"No, simply increasing the pore size of the air film will lead to greater pressure loss, which is not worth the gain..."

"Mr. Chang, if the cooling holes are changed from cylindrical to tapered, so that the inlet area is small and the outlet area is large, wouldn't it be possible to improve the coverage of the airflow on the blade surface?"

At this time, Chang Haonan was really impressed by him.

The cooling effect of special-shaped holes is better than that of round holes. This will be something that any undergraduate majoring in the relevant field will know in 20 years. However, at present, the research on this aspect in China is still blank.

In the previous life, it was not until more than a year later that Rolls-Royce went to Northwestern Polytechnical University to sponsor a research project related to active cooling that China realized this.

Engineering things are sometimes like a layer of window paper that has been pierced, and it looks like that. But if there is no one to guide it, it will take a lot of time just to find where the window is.

Liu Yongquan, at least in a short period of time, found the right direction.

"The idea is correct, but it can go further."

Chang Haonan took a pen and paper from the side and drew a diagram on the paper:

“In fact, there is no need to make major changes to the cooling hole itself. It is enough to connect an expansion section to the outlet part, that is, the end of the hole, so that the pressure loss is smaller, and the flow rate at the exit of the air film hole can be greatly reduced. "

"Reducing the flow rate means reducing the momentum. The cooling air will hardly blow away, and the wall adhesion effect is better."

"Moreover, the interaction between the mainstream and the cooling air is weak, and the kidney-shaped vortices on both sides of the jet are weak. The meridional area will form an anti-kidney-shaped vortex pair structure, which also enhances the lateral diffusion of the cooling air. It can make the cooling air film more even!”

"That……"

Liu Yongquan only had a feeling of enlightenment at this time. The solution to the whole problem seemed as simple as 1+1:

"Then we just need to change the round hole into this...this kind of special-shaped hole?"

"Of course it can't be that simple. What I just said is just the basic principles."

Chang Haonan put the pen aside, waved his hand and replied:

"The air film formed by the special-shaped holes not only improves the effectiveness downstream of the hole, but also increases the heat transfer coefficient of this part, so the cooling effect on the solid wall area with a low heat transfer coefficient is relatively poor."

"Furthermore, this awkward opening method will definitely affect the structural strength of the workpiece. We are building an aerospace engine, which has requirements for overload. Moreover, the environment of high temperature, high centrifugal force, and strong airflow impact itself is also a problem for the structural reliability. test."

"So, what kind of hole type should be used, how to design the distribution of air film holes on the surface of the workpiece, and how to design the angle of the hole channel - not only the pitch angle, but also the lateral angle, these are all issues and all have to be chosen."

"That's why I have to order a piece of equipment. On the one hand, it is to study specific air film cooling solutions. On the other hand, it is also to accumulate some data for the next major version of the TORCH Multiphysics software. The air-thermal coupling aspect is different from simple There is still a big difference in force-thermal coupling, and I’m afraid a new functional module is needed to do it well.”

Even Chang Haonan is not really omniscient and omnipotent. He has tried using his own software before, but there are too few theories and data in this area. Are the results of the simulation...

It can only be said to have certain reference value.

"Then Mr. Chang, let me design the experimental plan?"

Liu Yongquan behind him was already eager to try.

"Actually, I have already designed it..."

Chang Haonan glanced at the brand-new experimental equipment not far away.

"Ah this..."

Liu Yongquan scratched the hairless head in embarrassment.

But Chang Haonan changed the subject again:

"But you can also try it first, and then compare it with what I gave you after the plan is made."

Liu Yongquan's eyes lit up, and he suddenly felt that he could do it again:

"So... regarding the turbine sample for testing, should we just use the turbofan 9?"

"Yes, if you don't have the design data of Turbofan 9, you can directly ask the 430 factory for it."

Under Chang Haonan's operation, Turbofan 9 has now basically become the technical verification model of Turbofan 10.

Although the temperature in front of the turbine of the former is unlikely to reach the level of 1200-1250c, the cooling effect is definitely not too high.

Especially if there is no need to replace the blade material.

Of course, it’s not just the 430 factory.

The Spey MK202 is actually just an engine with a thrust-to-weight ratio of level 5. Its indicators other than fuel consumption are not even as good as those of many last-generation turbojet engines.

Some of the technologies tested by Turbofan 9 can always be used back in mass-produced models. On the premise that the cost and overall structure remain basically unchanged, the performance will definitely be improved.