Diagnostics of boundary layer transition by shear stress sensitive liquid crystals
Previous research indicates that the problem of boundary layer transition visualization on metal models in wind tunnels (WT) which is a fundamental question in experimental aerodynamics is not solved yet. In TsAGI together with Khristianovich Institute of Theoretical and Applied Mechanics (ITAM) a method of shear stress sensitive liquid crystals (LC) which allows flow visualization was proposed. This method allows testing several flow conditions in one wind tunnel run and does not need covering the investigated model with any special heat-insulating coating which spoils the model geometry. This coating is easily applied on the model surface by spray or even by brush. Its’ thickness is about 40 micrometers and it does not spoil the surface quality. At first the coating obtains some definite color. Under shear stress the LC coating changes color and this change is proportional to shear stress. The whole process can be visually observed and during the tests it is recorded by camera. The findings of the resea...
Optics of cholesteric liquid crystals
A review is presented of the theory of optical properties of cholesteric liquid crystals (CLC). The diffraction nature of the unusual optical properties of CLC is exhibited in the simplest and most easily visualizable kinematic approximation of diffraction theory. A quantitative description of the optical properties is given based on the exact solution of Maxwell equations for light propagated along the optical axis of CLC and within the framework of the dynamic diffraction theory for an arbitrary direction of propagation. Considerable attention is devoted to the manifestation of the connection between the structural and optical properties of the CLC observed when light is propagated at an angle to the optical axis of the CLC and when the CLC structure is distorted by an external field. Investigations of the optical properties of absorbing CLC reveal that suppression of light absorption in the selective reflection band is analogous in its nature to the well-known Borrmann effect in x-ray diffraction. Different approaches to the optics of imperfect CLC which frequently most nearly correspond to the conditions of actual experiments are described. A theory of the optical properties of chiral smectic crystals is presented. This theory, on the whole, is analogous to that for CLC, but it predicts a number of qualitative differences in the optics of chiral smectic crystals. The theory and special features of the Vavilov-Cherenkov radiation in CLC is briefly presented. A comparison is made of the theoretical results with the experimental data and the most promising directions for theoretical and experimental research are indicated.
Turbine blade temperature calculation and life estimation - a sensitivity analysis
Abstract The overall operating cost of the modern gas turbines is greatly influenced by the durability of hot section components operating at high temperatures. In turbine operating conditions, some defects may occur which can decrease hot section life. In the present paper, methods used for calculating blade temperature and life are demonstrated and validated. Using these methods, a set of sensitivity analyses on the parameters affecting temperature and life of a high pressure, high temperature turbine first stage blade is carried out. Investigated uncertainties are: (1) blade coating thickness, (2) coolant inlet pressure and temperature (as a result of secondary air system), and (3) gas turbine load variation. Results show that increasing thermal barrier coating thickness by 3 times, leads to rise in the blade life by 9 times. In addition, considering inlet cooling temperature and pressure, deviation in temperature has greater effect on blade life. One of the interesting points that can be realized from the results is that 300 hours operation at 70% load can be equal to one hour operation at base load.