How the new Federation / Eagle spacecraft was calculated. Interview with TESIS

Today, our blog is visited by TESIS Technical Director Andrei Aksenov, an expert in the field of aerodynamic and hydrodynamic calculations, the head of the team that is developing the FlowVision package.

On the eve of Cosmonautics Day, we took advantage of an acquaintance and asked how TESIS was involved in the project to create a new manned spacecraft, Federation, (the new name for the Eagle flight model).



How did your cooperation with RSC Energia begin, how did TESIS become a member of the Federation project?

NPO Energia of the General Ministry, and then RSC Energia of Roscosmos is our native organization, in which the founding fathers of FlowVision were students and graduate students, with whom they worked when they were employees of the Moscow Institute of Physics and Technology, then the Institute for Design Automation of the Russian Academy of Sciences, and then employees of TESIS .


Founding Fathers of FlowVision

In the late 80s, we worked on modeling the separation of biological products (drugs) under microgravity conditions at the Salyut-7 and Mir stations. Cosmonaut and scientist, fizteh, A.A. Serebrov, who directed this work in our group, brought biological products to Salyut-7 with his personal belongings for our experiments on the Ruchey installation. Biological products were prepared at the Institute of Medical Biotechnology, which was led by another prominent astronaut and scientist B. B. Egorov.

Further, NPO Energia attracted us to the calculations of launching the Zenit rocket from the Sea Launch launch pad. Then we made the first generation of FlowVision - it was written in Fortran, was parallel and worked on transporters. NPO Energia became the first user of FlowVision. There were other projects with NGOs, and then with RSC Energia.


One of the first versions of FlowVision

In the process of creating FlowVision of the second and third generation, we added new physics and new calculation methods. In the end, we learned to solve problems with bodies that move in the calculation domain and in the presence of water and air, and also calculate gas flows when there is simultaneously an incompressible and supersonic (or hypersonic) flow at almost any time steps. Such functionality was very useful to the aerodynamics department of RSC Energia in the design of the new Federation spacecraft (now it was renamed Orel). The enthusiasts of using domestic engineering calculation systems at RSC Energia were well-known aerodynamics who had already retired - Ph.D. Anatoly Alexandrovich Dyadkin and Doctor of Technical Sciences Andrey Georgievich Reshetin, one of my teachers.

What tasks were assigned to you, TESIS area of ​​responsibility?

When designing the “Federation” there were several tasks - they correspond to the various stages of launching a rocket with a ship, passing through the atmosphere, then descending from orbit to the ground and actually landing and splashdown.

At launch, we watched how the launch of the engines of the emergency rescue system (this is almost an explosion!) Affects the hull (impact), we looked at the discharge of the fairings at hypersonic rocket flight modes (Max = 6).

The worst thing is the return to earth. We worked on the descent and braking of the device at hypersonic speeds, when thermal protection ablation occurs (mass loss of thermal protection during high heating when entering the atmosphere at high speed), we calculated the shooting of the hatch of the parachute container (KLPK), then the braking engine is turned on (again, a small explosion , watched how the shock wave affects the ship’s hull), calculated engine braking and the actual landing.

Since the ship lands in the field, and not at the cosmodrome, the developers of the ship were interested in the effect of gas jets from the engine on the soil - would the return vehicle (VA) dig a hole under it and fall there? But where he was digging a hole, it’s on the water. Federation can land on water, but this is an emergency situation.

The most difficult task that we have solved and are solving in this project is flooding with the engines turned on. I can say for sure that no one in the world can simulate it. Here, supersonic jets, a moving body in the computational domain (the returnable device itself), which moves under the action of aerodynamic and engine thrust forces, and water, which moves relatively slowly and can be considered incompressible.


Modeling the interaction of the water surface with jet jets of landing engines of the returned vehicle

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TESIS was the only one responsible for the calculations or did several teams perform similar tasks in parallel?

Cosmonautics requires reliability, which is achieved not only by duplication of systems on spacecraft, but also by duplication of sources of data for design. Some of the tasks were done experimentally, some were solved by the engineers of RSC Energia themselves at FlowVision and programs of other companies.

The number of co-executors of this project is large, I don’t know everyone, or I can’t talk about everyone. However, I know that in aerodynamics RSC Energia cooperates with the strongest scientific teams, including a team from the St. Petersburg Polytechnic University, which is led by a live classic of turbulent flow modeling Mikhail Khaimovich Strelets, judging by the open publications.

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Of course, in our calculations we used our CFD code FlowVision (CFD - computational fluid dynamics, computational fluid dynamics). The code has the ability to solve unique problems - it’s splashing the apparatus, calculating the separation of the cowl flaps from the rocket, and our method of calculating the equations of motion of the liquid is “all-weather”. We call the method that allows one algorithm to calculate both an incompressible flow and a hypersonic flow. Our team left the school of academician O.M. Belotserkovsky, who laid the foundation for finite-volume algorithms for solving the Navier-Stokes equations. These algorithms are called "splitting methods for physical variables." We have substantially developed these methods, improved them and now they are “all-weather”. We put these methods into the FlowVision software package.

The adequacy of the results is a difficult question. First, to correctly solve the problem numerically, you need to know the answer by at least 50%. Assessment, empirical knowledge is a great tool that we use before starting the calculation.

Secondly, in computational fluid dynamics there are internal procedures showing the correctness of the calculation - this is the convergence of the solution over the grid, for example. This means that if the refinement of the computational grid does not lead to a change in the result, then the engineer is on the right track - most likely he will get the right answer. And thirdly, another procedure is validation. In this case, a similar problem is solved, but in which the result is known.

If the results of the calculations and the “answer” coincided, then the program and the calculation procedure are correct. Thus, scrupulously and tediously going through these procedures, we prove to ourselves and the customer that we get the correct results. By the way, grid convergence and validation are “guest” procedures. The FlowVision team took part in the development of these GOSTs.


External contours of the space head part with a manned transport ship and an emergency rescue rocket unit.

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Density field after triggering of the emergency rescue system (CAC). It is necessary to evaluate the shock loads from the jets of the CAC engines on the manned vehicle.

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Was FlowVision your primary CAE tool for numerical simulation in these works?

Yes, FlowVision was the main one. Although there are tasks where we will use a combination with programs for calculating the stress-strain state of structures. For example, when a ship hits the water, the bottom of the ship is slightly deformed, and the force of the impact changes. What code will be used for this is not yet decided, but there is a choice - from Western Abaqus or Nastran to domestic ones - APM or Fidesis.

How did the customer in the person of RSC Energia react to the fact that the calculations are carried out in Russian software?

In my opinion, the customer does not care which product to use - Western or domestic. The choice here is in the plane to solve the problem or not decide how much it will cost and how long we will solve. I have already said that only we can solve some problems, there is no choice.

How many estimated water landing cases are there?

I won’t tell you right away - you have to look in the statement of work, but there are dozens of them. This is landing on calm water, on a wave, at an angle, with and without engines. Moreover, the appearance and filling of the ship changes during the development process, which adds design cases, and we must keep up with the flight of design ideas.


Simulation of splashdown of a return vehicle

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How is wave landing calculated? Do you take any specific value for the characteristic of the wave (height, speed)?

The speed of the wave is determined by the wavelength, there is still depth, but we believe that the depth is infinite. So the parameters are wave height and wavelength. Well, and as usual, the splashdown speed of the device and where it lands - on the left side of the wave or on the right, i.e. essentially the angle of entry of the apparatus into the water. Plus, as I said - a parameter of the engines.

How much does each calculation case take when using cluster computing? How much faster than using a personal computer?

We consider tasks on four supercomputers - Tornado (South Ural State University), Lomonosov and Lomonosov-2 (Moscow State University), a cluster of the Kurchatov Institute. Some small tasks may well be performed on staff. But such people almost do not give us. RSC Energia may well make them on its own with its FlowVision license. But the “difficult” tasks fall to us. Since most tasks are non-stationary, the calculation can take from several days to a couple of months. The customer is interested in not one calculation, but dozens of different cases, so the tasks are considered simultaneously. It is unrealistic to make such calculations on a personal computer - they will last a year or years and no one is interested in the result after such a time.

The models of the returned apparatus and the hatch of the parachute container for aerodynamic calculations were simplified. How does this affect calculation error?

Models are simplified precisely so that there are no calculation errors. Although there was a funny case. RSC Energia, if you remember, was making the cool Clipper space plane. And the name is good (sea, wanderings, tea clipper Catti Sark ...), and the idea itself was beautiful. But ... let's not talk about it.

There was a “purge” of the Clipper model in the wind tunnel. And at some angles of attack on the curve Cy (C - lift coefficient) from the angle there was a certain "hump", which in theory should not have been. They began to consider this task in FlowVision - they got as in theory - there is no "hump". They began to think. We decided to see how the holder with the help of which the Clipper model is held in the pipe affects the aerodynamic characteristics obtained in the pipe - that is, they decided to simulate a model experiment ... It turned out that there is a hump! The moral of this story is simple: numerical modeling is necessary not only to replace the experiment, but often to explain it! I heard this valuable thought in TsAGI from colleagues who purged all our combat aircraft and created their almost perfect aerodynamics. Now they also consider new planes in FlowVision.


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Did you make simplified models in FlowVision or in a third-party system? In general, does FlowVision allow creating models: solid-state, surfaces, etc.?

When we started creating FlowVision, we immediately abandoned our geometric model generator. For us, SolidWorks was the main supplier of the model for us, simply because it was available and worked on Windows. And the beautiful COMPASS system at that time was two-dimensional.
By the way, the famous company EagleDynamics, led by my friend Igor Tishin, unfortunately, who recently left us, in addition to the Flanker toy, created the Z-CAD CAD system. She was three-dimensional and operated on surfaces of any complexity. At that time it was a cool system. We had views to use it in FlowVision, but the Z-Cad could not survive the 90s.

Now we have connected FlowVision to KOMPAS-3D, which has become a world-class three-dimensional system. Hybrid COMPASS and FlowVision named KompasFlow. Therefore, we can say that the geometry generator in FlowVision still appeared.


KompasFlow, external aerodynamics

In the FlowVision system you can get an animation of the movement of the returned device. Does animation help in solving any issues or is it much more important to get numerical values ​​(speed, coefficients)?

We gave this name to our program, because the idea is that if an engineer sees the flow, then he understands it. Flow - flow, Vision - vision. FlowVision - I see the flow, my students at FizTech have come up with a funny translation of "StruGlyad".

If the flow is unsteady, such as landing on water, or launching an emergency rescue system or landing engines, then animation is an understanding of the unsteady nature of the flow. Still, man did not descend from a monkey, he is a monkey, and best of all, we react precisely to movement, and not to a figure. If the engineer understands the course, the numbers will become clear to him. They say that a picture replaces 1000 words, I would add that animation replaces 1000 pictures.

But there is one more important point. FlowVision has some methods of visualizing flows that engineers usually do not use for analysis, because it is difficult to obtain quantitative data from them. However, these visualization methods (for example, three-dimensional visualization) together with animation are very important in order to show the calculation results to “generals”, i.e. people who depend on project financing, but who have little knowledge of the technical nuances of the project. In the modern world, it is impossible to survive without PR ...

What is the error of calculations in the FlowVision system in comparison with real tests?

The question is extremely complex, as it depends on the task. There are tasks where an accuracy of 3-5 percent is the limit. For example, the tasks of shipbuilding. The science of shipbuilding is more than 300 years old, and there they learned how to get accurate results. But the usual norm for technology is 10-15 percent. And often just a good coincidence is important. Design optimization can be done in this way, simply improving some characteristics without knowing their exact value. You can lose weight on the wrong scales.

Are you planning further work with your participation on the development of the returned device?

We really hope that our cooperation will last for many years. RSC Energia is one of the world's key firms that creates manned spacecraft. By the way, probably, some will read our material here and ask: “Why do you need to fly into space? Isn’t it easier to use these huge funds to improve life on Earth? Say, in Russia, we repair roads and replace fools. ”

This question used to baffle me. You can argue as K.E. Tsiolkovsky: “Humanity will not remain forever on earth, but in pursuit of light and space ... it will conquer all the space around it.” Or like Stephen Hawking, who believed that humanity would eventually exhaust the Earth’s resources and space flights - this is the key to its survival.

However, from my point of view, these are not entirely convincing answers - the opponent of flights into space will easily challenge these arguments. More convincing is the well-known experience with mice that created ideal living conditions, and after 50 generations they stopped reproducing and became extinct. If humanity is not set global tasks, if not forced to overcome difficulties, we will simply die out like those mice. Space "gives birth" to precisely those passionaries of Lev Gumilyov who will move humanity forward and prevent it from becoming extinct.

Therefore, I hope that the firm of the great designer S.P. The queen will always be afloat. Well, we are with her ...