Chapter 381 Designing a DSI inlet duct to practice (page 1)

Young people who have just joined the workforce are often very passionate, especially after being given direction by Chang Haonan himself.

The nose wing is a relatively independent aerodynamic component. Due to its relatively small size, it will be in a contracted state during level flight or low angle of attack flight. It will not affect the normal aerodynamic shape of the aircraft. Only when the angle of attack It will start and take effect only after it breaks through a certain threshold.

And this process obviously cannot be performed manually by the pilot.

Therefore, where to set this threshold and what the length and width of the nose side strips are to obtain the best side strip vortex are the "jobs" left to Lin Tongxin.

As for Sun Huizhong himself, he is naturally responsible for a more important task——

Under the guidance of Chang Haonan, the design and optimization of the DSI air inlet of the advanced trainer aircraft was completed.

As a completely non-adjustable type of inlet, the biggest problem with the DSI inlet is that it only has one configuration. Therefore, the optimization interval is constant and must have a large optimization interval width.

It doesn’t matter if the optimal optimization range of the rectangular baffle air inlet is only Mach 0.01. Anyway, as long as the flight control is strong enough, the position of the baffle can be adjusted to ensure that the air intake efficiency is always in the optimal state.

However, if the fixed air inlet is made like this, slightly changing the flight speed will cause the air intake efficiency to drop drastically, and even the boundary layer cannot be blown away, resulting in strong air intake distortion, which will affect flight safety.

In short, it requires a high level of design and experience to achieve a satisfactory optimization state for aircraft using DSI inlets.

Moreover, Project No. 10 is a key project with a name at the highest level, and every move it makes will attract the attention of countless people.

After the No. 01 prototype using a three-way adjustable air inlet takes off for the first time, it needs to undergo major changes, so it is necessary to produce sufficiently convincing data.

As it happens, the common speed range of advanced trainer aircraft is much smaller than that of fighter jets, and the optimization difficulty of the relatively traditional aerodynamic layout is also lower than that of the J-10 using a canard + delta wing configuration.

A perfect opportunity to practice.

"Gong Sun, you must make sure you fully understand what I'm going to say next. If there's anything you don't understand, ask me right away."

Chang Haonan turned on his computer, pulled out several design files that he had already prepared, and then motioned to Sun Huizhong to move two chairs from the side.

For him nowadays, many times he no longer has to do everything by himself, especially when there is a helper around him.

"clear."

Sun Huizhong quickly sat next to him.

"As for the basic principle of DSI inlet, I have already talked about it when I was in Chengdu. Simply put, it uses the characteristics of the cone shock wave itself to form a strong pressure gradient on the convex hull surface at the lip of the inlet. , blowing the fuselage boundary layer at this location directly out of the air intake opening to reduce the negative impact of the boundary layer on air intake efficiency."

Having said this, Chang Haonan called up a pressure distribution map that he had asked Yao Mengna to help draw some time ago. It was tested using a DSI inlet model under ideal conditions.

It can be clearly seen from the above that the convex hull structure uses the pressure difference to directly "push" the shock wave out.

After confirming that both Sun Huizhong and Lin Tongxin had no doubts, he officially entered the key design part today:

"It can be seen from this principle that the core of the DSI air inlet design is the shape of the convex hull structure. Through theoretical and numerical analysis of the waverider, I have summarized two design convex hulls. Methods."

"I remember you said before that you should select a number of tracking points from the leading edge of the conical surface, and start tracking from these tracking points to the downstream of the flow field in the flow field..."

I have to say that Sun Huizhong definitely put his heart into it when he was in Rongcheng.

I can even remember such details.

"Yes, this is the generating body method, also called the cone guide method. It is also the basic principle of the most traditional method for designing DSI inlets. It is relatively intuitive and easy to understand, and the design process requires less calculations. So at the beginning of this year , it was the first method I considered.”

Chang Haonan nodded, but then his tone changed and he said:

"But recently I just happened to design a new numerical calculation tool whose calculation efficiency is much higher than that of traditional software, so the limit on the amount of calculation becomes much smaller, so I developed a new numerical calculation tool based on the generative volume method. The second method is the close cone method.”

"The... second method?"

Sun Huizhong felt that his brain was a little weak at this time.

Designing a DSI air intake is inherently a difficult task. Even the United States has only installed a relatively simple early version on an improved F16 technology verification aircraft.

The JSF Joint Strike Fighter, the first mass-produced model planned to use DSI inlets, has just begun to be selected.

In short, it is still in the exploratory stage of design.

As a result, you have already summarized a complete set of methodology, and it also includes two solutions?

It’s totally unreasonable…

"Yes, the second method is more accurate than the generating body method, because this method does not need to presuppose a geometry, but directly gives a curve describing the shape of the shock wave at the exit of the waverider, and divides this curve into There are countless small arcs. Each arc can be considered as a part of the shock wave curve, and the cone that generates the shock wave in this section is the close cone. The plane that is close to the axis of the cone and orthogonal to the arc is called the close surface..."

"..."

"The corresponding close cone is obtained on each arc of the shock wave curve, and finally a series of streamlines are obtained by tracing the leading edge curve, which together form the lower surface of the DSI inlet convex hull."

"This design method is more flexible and can meet the requirements of various flow sizes and various air inlet geometries. That is, it can adapt to any engine by adjusting different shock wave curves without having to adapt the engine to the inlet. The final product The performance will naturally be better.”

At this point, Chang Haonan turned around and saw two pairs of simple eyes.

Obviously, the leap in thinking just now seems a bit too big.

It is really difficult for engineers with average mathematical theory skills to fully accept the principles in a short period of time.

"Let's calculate it using two methods."

He is going to demonstrate it in the simplest way:

"We first assume that the shape of the inlet shock wave is a quadratic curve z=-ax^2+b (a>0)."

Chang Haonan wrote a quadratic function directly on the paper.

"Uh... Director Chang, the shock wave shape is so simple..."

While Chang Haonan was lowering his head to write, Lin Tongxin originally wanted to ask why the shock wave curve was in such a simple form.

But the words stopped abruptly mid-sentence.

Because Chang Haonan wrote the second function on the paper.

"And such a combination of parametric equations and curves."