**1. Introduction**

Currently, light-gas cannons are one of the most effective devices for accelerating shells of relatively large mass to speeds comparable to the orbital. In this area of research, intensive and extensive experimental work is being carried out to study high-speed impact, resistance of materials to high-speed action of solid particles, hypersonic flows around axisymmetric bodies and are closely related to the development of aviation and space technology. In this case, some types of guns with the replacement of the accelerating channel by the Laval nozzle can be effectively used to study hypersonic flows around bodies, since the parameters of the working gas required for high-speed throwing and generation of a hypersonic air flow are identical. High-speed throwing system parameters and technical requirements are described in [1–5]. Since the 40s of the 20th century the generation of hypersonic flows, development of measurement methods and study of such flows structure over various test bodies were carried out by researchers from all over the world [6–16]. Numerical modeling methods mentioned, for example in [10, 11, 17–19], were added to the experimental tools of the research with the development of computer technology. However, it should be noted that experimental studies of hypersonic flows around the objects are still preferred. Due to the importance of problems to be solved flight tests are often used for higher authenticity of the experimental data. Usually total and static pressure is measured by means of Pitot-Prandtl probe to determine

the Mach number, but in large number of research works measurements are not carried out due to complicated experimental techniques. Researchers [6, 7, 11–16] used the initial Mach number calculated from Laval nozzle geometrical parameters. Pressure measurement using a Pitot-Prandtl probe and temperature measurement using a thermocouple significantly distort the flow structure, complicate the design due to the need to place measuring elements inside and on the surface of the models under study, which, in the absence of flow visualization, can introduce uncontrollable errors in the experimental results. In hypersonic aerodynamic facilities preferable methods of research are optical methods with high-speed cameras as the reg-istering devices. Methods of optical visualization of supersonic flows include a method of a laser knife, smoke visualization, visualization by means of the spark discharge, etc. [13, 15, 16, 18]. Optical methods based on the relationship between the optical and thermodynamic properties of the medium (shadow methods, interference methods, spectral diagnostics) allow measurements in hypersonic flows with high accuracy. In some cases, to visualize and measure the temperature field on the surface of the model, a thermosensitive coating is used as an alternative to measurements using thermocouples [8, 9]. Research in the field of high-speed impact and diagnostics of hypersonic flow are often interrelated tasks, which makes it necessary to create experimental installations equipped with systems for optical visualization and diagnostics of the flow and measurement of the Mach number, which makes it possible to study hypersonic flow around objects without suppressing the investigated gas flow.
