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Aerodynamic efficiency of the nozzle cascades of steam and gas turbines is defined by many factors and one of them is the tangential and radial nonuniformity degree of the parameters of a spatial flow behind the cascades. The averaging of these parameters enables the determination of the integral parameters of the cascades, in particular two flow angles and the velocity angle or the kinetic energy loss coefficient. The angle that takes into account the level of the averaged radial component of the velocity defines the level of kinematic losses in the cascade. Even in the case of the cylindric boundaries of the cascade this angle differs from zero and kinematic losses decrease the cascade efficiency by 30 to 50 percent. This scientific paper gives the results of experimental investigations of the effect of the circumferential nonuniformity of the velocity and the angles of the spatial flow on kinematic losses at different radii of the nozzle cascade of the last stage of the steam turbine and the nozzle cascade of the first stage of the gas turbine. The kinetic energy loss coefficient and the coefficient of total losses were suggested as the integral characteristics of the cascades. In the case of cylindric boundaries of the stage the total loss-to-kinetic energy loss ratio is noticeably decreased during the transition from the average zone to the zone of end losses. However, in the peripheral zone of the nozzle cascade of the last stage of steam turbine total losses are three times higher than kinetic energy losses due to the fact that the radial component of the velocity behind the cascade is much higher than the flow rate component and the level of the losses of kinetic energy is not high.

The obtained research data are given for the nozzle cascade used by a small-size gas turbine of an average fanning in combination with the radial diffuser. Aerodynamic characteristics of the nozzle blade cascade were determined in a wide range of a change in the Reynolds number varying from 4∙105 to 106 and the reduced velocity varying in the range of 0.4 to 1.13. The flow rate coefficient of the nozzle cascade was derived for all modes using the integral methods and the drainages behind the cascade. The kinetic energy loss coefficient and the flow angles were calculated using the measurement data of flow parameters in three control modes that were obtained due to the use of orientable pneumometric probes. When the expansion degree of the convergent –divergent annular duct behind the cascade is equal to 1.43 the flow in the narrow section of this duct is “enlocked” in the mode when the reduced velocity behind the cascade is equal to 1.127. At such velocity the Reynolds number 106 is self-similar for the flow rate coefficient. At lower values of Reynolds number, the decrease of it is accompanied by an intensive decrease in the flow rate coefficient for all the values of the reduced velocity. For the Reynolds number lower than 7∙105 an increase in the velocity results in a decreased flow rate coefficient. When this number exceeds 8∙105 an increase in the velocity results in an increase of the flow coefficient up to the moment when the flow is “enlocked” in the nozzle cascade.

To smooth the parameters of the three-dimensional flow behind the nozzle cascade new methods were suggested that allow us to sustain the flow rate, stagnation enthalpy and the axial projection of the moment of momentum for initial-, nonuniform and averaged flows. It was shown that the choice of the fourth integral characteristic (the kinetic energy, the entropy and the quantity of motion) has no particular significance because it has no effect on the complex criterion of the cascade quality, i.e. the velocity coefficient-angle cosine product that characterizes the level of the radial component of velocity. The minimum values of the velocity coefficient and the cosine angle satisfy the method that allows us to sustain the quantity of motion during the smoothing and the maximum values of the specified nozzle characteristics satisfy method 2 that enables the entropy maintenance. To evaluate the aerodynamic efficiency of the nozzle cascade the preference should be given to method 1 that enables the kinetic energy conservation and the velocity coefficient allows for the precise determination of the degree of loss of the kinetic energy that is equal to 3.6 % as for the example given in the scientific paper. As for method 1, the kinematic losses in the cascade are defined by the angle cosine that characterizes the level of the radial component of the velocity behind the cascade. For the example in question, kinematic losses are equal to 1.9 % and the complex criterion of quality equal to 0.972 corresponds to the overall losses of 5.5 %. It was suggested to use the velocity coefficient and the two angles of flow as integral cascade characteristics. The use of these characteristics enables the correct computations of the efficiency factor for the stage within the one-dimensional computation. The incisive analysis was performed for different methods used for the averaging of the parameters of the axially asymmetric flow behind the nozzle cascade. It was suggested to neglect the flow rate factor in the case of thermal computations done for the turbine stage.

The objectives of research done were to define the aerodynamic characteristics of the different axial-radial diffusers constructions on load-changing turbine operations with the purpose to find their aerodynamic improvement reserve. Using the CFD program, the numerical analysis of aerodynamic characteristics has been performed for the four options of outlet axial-radial diffusers used for the steam turbine K-325-23,5. The flow for all four options of the diffuser was calculated for preset constant total pressure and total temperature at the channel input and the static pressure at the diffuser output. The data was taken from experiment that had been performed by department of turbine construction of NTU “KhPI”. A comparative analysis of the aerodynamic characteristics of the diffusers was performed and the values of the coefficients of total losses were defined. A version of the outlet axial-radial diffuser was suggested for the turbine that provides the lowest coefficient of total losses and better flow distribution through entire channel.

The objectives of research done were to define the geometric characteristics of the fairing of axial-radial diffuser that provide the lowest overall loss coefficient (the sum of the coefficients of internal losses and output velocity losses) and evaluate the possibility for the non-use of straightening grids behind the rotor of the last stage of compressor. Using the CFD program we conducted the calculated analysis of aerodynamic characteristics for the five options of outlet axial-radial diffusers used for the axial compressor of the gas turbine plant GT-6-750. The flow for all five options of the diffuser was calculated for preset constant total pressure and total temperature at the channel input and the static pressure at the diffuser output. The angles of incidence of the flow into the channel were varied in a wide range of the values for all the options of the diffuser. A comparative analysis of the aerodynamic characteristics of the diffusers was performed and the values of the coefficients of total losses, internal losses and output velocity losses were defined. A version of the stage by-pass was suggested for the diffuser that provides the lowest coefficient of total losses in the entire range of a change in the angles of flow incidence. The diffuser of this type has a considerably reduced intensity of separation phenomena in the input axial circular channel section and in the radial channel section. For the diffusers of this type with a short input axial section and substantial radiality a conclusion was drawn up that the use of straightening grids after the rotor of the last stage of compressor is inexpedient.

Small-size turbines of the aviation gas-turbine plants differ by their high output losses and a high sensitivity to the value of radial clearance over the rotor blades. An increase in this clearance, for example, in-operation results in the reduced power efficiency factor due to a change in the losses in the nozzle, in the turbine wheel and output losses. Test data of the cascade of an average reliability with the rotor blade height of 20.73 mm were given for the three clearances, in particular 0.22; 0.6 and 1.0 m. An increase in the losses in the upper zone was recorded for rotor and nozzle blades with an increase in clearance. It was shown that due to a change in the distribution behavior along the radius of absolute velocity С 2 output losses can either be increased or decreased or remain unchanged at a change in the clearance depending on the averaged angle of flow output from the cascade in the absolute motion α 2. To improve the methods of one-dimensional computation of the cascade using the integral characteristics of its lattices the method of definition of output losses was suggested taking into consideration radial nonuniformity of the velocity С 2 at a high clearance value. It is assumed that the flow velocity С 2 is constant along the radius at a minimum clearance value of 0.22 mm. A degree of the radial nonuniformity of velocity С 2 was taken into consideration using the cascade test data in different modes and at different clearances. The obtained test data on the influence of clearance on absolute losses with the output velocity are naturally not multi-purpose, because even for the cascade investigation, the kinetic energy of flow behind it depends not only on the clearance value and the averaged output angle but also on some other auxiliary factors.

The data of computational aerodynamic investigations carried out for the diffuser used by the discharge nozzles of modern steam turbines have been given. The calculations were done using the axisymmetric statement for the three options of flow turn to the collection chamber of exhaust nozzles. During the computation, we varied the parameters of special flow injection at the external diffuser by-pass and took into account the above-shroud leakage. The following characteristics were analyzed, in particular the flow injection jet pulse coefficient and the coefficients of net, internal and outlet velocity losses of the diffuser. It was shown that the outlet velocity loss produced the basic influence on the level of net losses of the diffuser due to the flow pattern and the availability of separated circulation zones, and the diffuser flow and the flow of nonaxisymmetric collection chamber of the exhaust nozzle are subjected to the substantial influence of flow injection parameters. Optimal parameters of the injection jet were determined taking into consideration the flow discharge from the exhaust nozzle into the capacitor of a cellar type. The recommendations were given on how to improve the aerodynamic characteristics of the diffuser due to a change in the structure in the region of special injection of the flow. A circumferential change in the size of the output slit of circular channel at the invariable total area of steam output allows for a decrease of mixing losses in the collection chamber and circular nonuniformity of the pressure behind the last cascade for the diffuser cowling flow without separation that results in a decrease of the net losses of exhaust nozzle. Proposed recommendations can be used to provide special injection of the flow of wet steam mixture removed from the circumferential zone of the last stage, increasing thus the efficiency of the exhaust zone of steam turbine with the cellar arrangement of the capacitor and retaining the erosion reliability of the last stage of low pressure cylinder.

Comparative design investigations of axiannular divergent cones were carried out using the CFD software. Turbulence models built-in into the CFD–software were used for the computations, in particular Spalart-Allmaras (S-A), k–w Shear Stress Transport (k–w SST), V2F. The aperture angle of the external by-pass of cones varied in the range of a = 11°–36°, while the cone expansion degree varied as n = 2–4. The data of CFD computations were compared with the known experimental curve obtained by Klein and confirmed by Zariankin, which divides the plane (a–n) into two regions: unseparated flow and separated flow regions. The region above this curve represents the separated flow in the cone at any combination of parameters (a–n), and the region below this curve represents the unseparated flow. The computations done using the CFD-software for axiannular divergent cones in the studied range of the relationships of geometric parameters (a–n) showed that the use of k–ω SST and V2F models results in the flow separation in the cones situated in the unseparated flow region, which runs counter to the experimental data, and the use of the turbulence model S-A provided the unseparable flow in the region below the experimental Klein curve and resulted in the flow separation in the region below this curve. Design investigations showed that the turbulence model (Spalart-Allmaras (S-A)) provides an opportunity for the satisfactory simulation of unseparable and separable flows in the cones of this type.

The leakage above the rotor wheel in the last turbine stage can positively influence the characteristics of the diffuser acting by analogy to the special inflation of the flow into the boundary layer in the external bypass of the diffuser. Contemporary structures of high pressure cylinders are equipped with axial-radial diffuser or diffuser installed in the exhaust pipe branch; therefore the problem of influence of the above-shroud leakage in the last stage on the aerodynamics of the exit diffuser of high pressure cylinders is rather vital. Computing investigations were carried out using CFD of the axisymmetric axial-radial diffuser peculiar for the exhaust pipe branches of high pressure cylinders of steam turbines in a wide range of pressure variations that define a value of the above-shroud leakage in the rotor wheel of the last stage. The flow behavior in the diffuser, the coefficients of losses and the pressure distribution on the diffuser cowling have been studied. It has been established that at the minimum values of leakage, which is peculiar for the seals of a cellular structure the flow in the diffuser is detachable and a coefficient of full losses has maximum values and at an increased above-shroud leakage that occurs in the traditional seals of a labyrinth type the point of flow separation from the cowling shifts towards the exit section lowering considerably the coefficient of full losses.

Highly accurate multi-dimensional potential energy surfaces have been computed in a fully automated fashion using newly implemented grid computing capabilities, which allow for the use of an unlimited number of cores. This new feature, which has been interfaced to our potential energy surface generator, allows for the accurate investigation of molecular systems, which are significantly larger than reported in the recent literature. Multi-dimensional potential energy surfaces at the coupled-cluster level were generated for systems of up to 16 atoms, which were used to compute accurate anharmonic vibrational spectra, which can directly be compared with experimental data.