TsAGI is a leader in aerophysical measurements
Measuring equipment is mostly small in size, which is its major advantage. However, despite its small size, it plays a significant role in the creation of any aircraft, be it a magnificent airliner or a maneuverable fighter or multifunctional helicopter.
The Central AeroHydrodynamic Institute named after N.E. Zhukovsky, TsAGI, is actively developing, improving and implementing measuring equipment. It allows developers of aerospace equipment to watch their creations in testing, and then to improve their performance for more efficient and safe operation in the real world.
TsAGI holds a leading position in metrology and measurements. This is evidenced by the fact that the innovations developed by the Institute are in high demand both in Russia and abroad. Chief metrologist of TSAGI, Head of Measuring Equipment and Metrology Department Vasiliy Petronevich spoke about the new developments.
— Vasiliy, in which areas has your department made particularly significant progress recently?
— Perhaps the most important achievement is that we have implemented a number of innovative projects. For example, we obtained new results in the field of high-precision strain gauge transducers, multicomponent aerodynamic tensometric balances, and special metrological standards.
I especially would like to note that an important stage has been completed in the creation of a new generation multi-channel pressure module, developed together with our partners. It has been designed to measure pressure on the model surface during aerodynamic tests. The work on this product, called “Inser,” commenced about four years ago. Together with Driver LLC (Saransk) we developed a
In 2014, MMD-32 modules were tested in the industrial transonic wind tunnel (ADT T-128) and confirmed their metrological performance in a real experiment.
Today, Inser Series MMD-32s have reached a high level of readiness. We have already submitted all the necessary documentation to Gosstandard, and soon our joint development will be certified and included in the State Register of measuring instruments of the Russian Federation.
In just three years we managed to move from prototype to the final product, that is, in fact, to create a new generation of multi-channel pressure-measuring devices. This is a major achievement in national instrument engineering.
Along with TsAGI, these modules are already installed at experimental facilities of MKB Raduga, FSUE SibNIIA and MIPT.
— What are the advantages of the new generation modules?
— Their main advantage is their dimensions. Having comparable accuracy, they are approximately 3 times smaller than their equivalents, including foreign counterparts. This makes it possible to increase the number of measurement points, to place the equipment in smaller structural elements and, consequently, to increase efficiency and information content of an experiment.
The presence of thermostabilizers in new generation modules is another advantage. It is known that to improve accuracy, the temperature of the modules during the research should be constant at 60˚ C. Previously these conditions were met by using large external equipment and multiple cables. Now the unit is only connected to a power supply. It provides thermal stabilization and operation of sensors and the digital part.
— What kind of equipment was used previously: domestic or foreign?
— In the mid-90s of the last century, our department developed its own
— How is the measurement carried out in with the modules?
— The small device is installed in a structural member of the model, such as the fuselage. The model is drained, i.e., small holes are drilled, connected to the measuring unit with thin tubes. During the experiment, researchers are using the modules to examine how the incident flow pressure is distributed across structural members.
— Do we have to drill the model anyway to measure the pressure?
— There is an alternative to draining — the so-called fluorescent pressure transducers method [FPD — editor’s note]. It is the only non-contact method to measure pressure on the model surface. To carry out the test, the item is coated with a special paint. It contains fluorescent molecules that are excited by light of an appropriate wavelength. When the pressure is changed, the intensity of luminescence changes as well, as measured by digital cameras. This method is less accurate that draining, but it allows us to see greater spatial resolution of the pressure on the entire surface under review. TsAGI gives priority to the creation of this method. It was born in the Institute and spread to the entire world from here. And today we make extensive use of this method in aerodynamic tests in industrial tunnels under domestic and foreign contracts. In 2014 TsAGI for the first time employed the FPD method to study sonic boom in wind tunnels. This is an important step towards creation of a supersonic civilian aircraft.
— It’s kind of a graphic visualization of the airflow around objects?
— Yes, we get a color picture, but each color corresponds to a certain pressure. The pressure distribution can be integrated and forces derived acting on the structural components of the aircraft. FPD is a quantitative method. By the way, it has no alternative when it comes to testing small models where even the new modules cannot be placed.
We also have reached significant progress in the field of high-quality imaging. I am referring to liquid crystals.
— You talk about the technology used in LCD displays in cell phones and modern TVs?
— Not really. But we can say that these two technologies have similar physical effects. In LCD displays, crystals are sensitive to the electric field, and in our case they are sensitive to friction stress. When we decided to try imaging method using such liquid crystals, it turned out that those can not be bought, they are simply not in the market. And in 2010 we started cooperation with the Institute of Theoretical and Applied Mechanics (ITAM) of the SB RAS, which had the experience in production of liquid crystals, however, generally sensitive to temperature, not friction. They began to develop this product for us. And we, in turn, started testing models, as well as the creation of experimental methods and measurement systems.
— How do the crystals feel the change in flow current?
— Crystals deposited on the surface of the model act as diffraction grating. As the friction grows, grid spacing increases and the color of light reflected by the coating changes. This allows you to see the transition from laminar boundary layer to turbulent one, shock waves falling on the surface, as well as flow separation areas.
Friction forces in subsonic and transonic wind tunnels are different and may vary up to 100 times. Obviously, we cannot use the same type of crystals for all tunnels, i.e. we use different crystals for different tasks, creating new methods. Earlier we conducted a full cycle of research of the methods at subsonic flow speeds. And in 2014 for the first time we made a full-scale visualization system using liquid crystals in the T-128 transonic wind tunnel, and tested it.
However, it should be understood that the method cannot be created quickly; it is a long and laborious process. Furthermore, our goal is to move from friction imaging to quantification. This job is going to take years.
— Generally speaking, what are the outcomes of these new developments and methods for the aviation industry?
— Using these new methods and measuring instruments, the researchers obtain experimental data needed to improve aircraft and enhance its aerodynamic performance. This will improve the effectiveness, efficiency, environmental friendliness and safety of the aircraft being developed, and therefore, improve competitiveness of the national aviation industry.