After Chief Master Yu left, Professor Zhu, who introduced Yang Hui to Beihang University, left, and Yang Hui took more than a dozen 'scientific researchers' from the base and a dozen or so graduate students from Professor Zhu to start the specific test of aerodynamic data.

There are many aerodynamic tests of aircraft, including: dynamic simulation test, multi-body interference and separation test, aeroelastic test, dynamic derivative test, large angle of attack unsteady test, tail spin test, wind model free flight test, hinge moment test, etc., and all kinds of large test items add up to more than ten major types.

Airplanes belong to aircraft, but not all aircraft are aircraft, and the wind tunnel test of some aircraft is unique, such as parachute test and Manus effect test, these tests are not the test items required by the aircraft.

The most critical of the various wind tunnel tests of the new machine is the jet power air inlet test, which is also a major operation for the new maneuver, because it is necessary to change the nose air intake to a two-rib air intake, which is more troublesome to change.

The change of the air inlet of the new aircraft must ensure the working needs of the engine, which has a very important impact on the working efficiency of the engine, whether the engine can work normally, and the thrust of the engine.

The role of the air intake in the fighter is further emphasized, the fighter to achieve the deceleration and pressurization of the high-speed airflow, the first step is in the air intake, and the large subsonic civil airliner can almost be said to have no air intake, some are just an engine pod.

The air intake tract of modern fighters can be divided into adjustable and non-adjustable according to the working mode, or can also be divided into three-dimensional axial symmetry and two-dimensional rectangle according to the working condition.

The J-7 aircraft adopts a two-shock external ramjet three-stage adjustable supersonic air inlet with a central cone to meet the requirements of high-altitude supersonic flight. However, after the new machine was changed to two-rib air intake, there was a new problem, and it was necessary to know that the air intake channel must match the working conditions of the engine to be a good air intake.

J-7 is a two-speed sonic fighter with excellent performance, after exceeding 1.5 times the speed of sound, the low-speed flight air inlet will not meet the needs of the engine, which requires the J-7 to use an adjustable air inlet in the design to change the inlet cross-sectional area of the air inlet and discharge excess airflow.

The two-rib air intake is already a bit of a weight, and if you add a bulky adjustment mechanism, you can imagine what the new air intake will look like.

Therefore, in the design of the air inlet of the new machine, through Yang Hui's multi-party coordination, the high-speed performance of the new machine was discarded, and the low-speed performance was first ensured, followed by the solid high-speed performance, so this is simple in the design.

If you don't pursue high-speed performance, the Mach number of natural flight will come down, so you don't need to consider the air intake efficiency when flying at high speed in the design of the air intake, and the complex inlet section adjustment mechanism can almost say goodbye.

In addition, the new small ducted vortex has a greater demand for airflow, so it is only necessary to consider extreme cases, and the installation of a deflation valve is enough to deal with it.

Considering the flight requirements of the new aircraft, the simple structure of the pitot tube inlet is the best choice, although it is the least efficient air intake, but as long as the requirements are met.

The initial design of these air intakes is written into the document, and the people involved in the design can see it, and Professor Zhu said that it is feasible for the new machine to use this simple air intake, so it is necessary to prepare to test the shape of the air inlet of the new machine.

That's right, it is tested, not designed, and at present, it is the most reliable plan to pass the actual wind test. Professor Zhu first arranged the test item of this air intake.

"Looking at the initial design is to change the nose air inlet to a two-rib air intake, then we must take into account the influence of the attached surface layer, which is a big project for the thickness of the attached surface layer that we are going to test now."

How do you explain the attached surface layer? To put it simply: there is a stickiness in the air flow, and in the two-rib air intake design of the new machine, the air flow will flow through the surface of the nose before reaching the air intake. In this process, the air flow friction with the surface of the nose, and at the same time, due to the viscosity of the friction airflow, the air flow close to the surface of the nose will become slower than the other air flow, and this slow air flow is called the surface layer.

Aircraft engines do not allow the surface layer to enter the air intake tract, because the surface layer airflow will form a small area of slow airflow, which is incompatible with other high-speed airflow, this kind of incompatible airflow is called: airflow distortion. Distorted airflow can induce engine surge, which in turn can cause the engine to shut down.

Therefore, the engine must isolate the surface layer, and there are many ways to isolate the surface layer.

In the early days, the nose near-air and independent engine pods did not need to consider the surface layer, because in these two air intake schemes, the incoming flow did not flow through the surface of other objects, and naturally the surface layer was not generated.

For the military aircraft with two rib air intake, the only way to isolate the airflow of the surface layer is to use the surface layer partition to separate the airflow of the surface layer, so the problem comes, the difference in the aerodynamic shape of each aircraft will lead to the strength and thickness of the air flow of the surface layer.

In order to determine the installation distance between the partition and the body, it is necessary to test the thickness of the airflow of the surface layer, and then it is necessary to do the actual test in the wind tunnel.

Of course, the airflow of the attached surface layer partition itself will also produce the airflow of the attached surface layer, but the airflow of the attached surface layer is not strong, and it is only necessary to set up a vent hole on the inside of the partition to suck the attached surface layer away.

In order to meet these practical tests, theoretical calculations and analyses need to be carried out in the early stage, and then wind tunnel tests are carried out to test the steady-state performance and dynamic performance.

The theoretical analysis in the early stage takes time, and the production of the wind model also needs to be carried out, and different test models are used for different test projects.

For the production of test models, there are also different scales.

First, the length of the model should not exceed the height of the test section;

Second: the length of the model should not exceed 0.6 times the width of the test section, and the wing can cut off the outer wings, only ensuring the wing section above the air intake.

Third:

The production of experimental models is also a science, and if you don't study it well and make it according to the rules, you won't be able to measure the correct data.

Of course, it is not Professor Zhu who does theoretical analysis by himself, but a group of students led by Professor Zhu are Professor Zhu's best coolies, and it is the biggest waste to let Professor Zhu personally do complicated and relatively low technical theoretical analysis.

"Liu Jun, bring your test team to analyze this surface layer theoretically, and then we will conduct the actual test, we have a rare opportunity for this project, you have to study hard."

As a teacher is like this, you have to think not only about the problems that should be considered in the usual projects, but also about the education of these students, so it is really difficult to be a teacher in charge, especially if you are doing higher education.

Professor Zhu said that Liu Jun walked out with a few classmates, and at first glance he felt like a down-to-earth student, but what was surprising was that this Liu Jun did not wear eyes, which inevitably made people wonder how this guy's academic career came about.

Touching the stubble on his head, he accompanied his down-to-earth face, and said with a smile: "This theoretical analysis is our strength, and we must ensure that it is completed according to quality and quantity." ”

After speaking, Liu Jun took people to the side to do theoretical analysis, nodded Professor Zhu whispered to Yang Hui.

"This Liu Jun is the most academically accomplished among my students, and there is absolutely no problem for him to do this theoretical analysis now."

Yang Hui is not worried about this, as long as the theoretical analysis is accumulated enough, it will naturally be handy, and if there is still a problem with a group of graduate students doing this, it will be strange.

Yang Hui was wondering if this aerodynamic design could be started with several more projects at the same time, one by one, but it was really impossible to make effective use of time.