Włodzimierz Wróblewski

Optimization of Cooling Passages Within a Turbine Vane

The trends in gas turbine technology aim to build more and more efficient cycles, which is usually achieved by the temperature increase at the inlet of the turbine. To prevent the negative effects of elevated temperature some actions are taken concerning, among others cooling of the high temperature components. Since the structure of the cooling system affects the turbine performance, it is essential to carry out the optimization to make it as efficient as possible. In this paper we show some aspects of passage optimization for internally cooled gas turbine vanes. In the present study the vane profile is taken as aerodynamically optimal. The analysis involves the optimization of the location and size of circular cooling passages within the vane. The analysis is performed by means of the genetic algorithm for the optimization task and FEM for the heat transfer predictions within the blade.Copyright

Thermo Mechanical Optimization of Cooled Turbine Vane

This paper discuses the problem of cooling system optimization within a gas turbine vane regarding to thermo-mechanical behaviour of the component. The analysis involves the optimization of location and size of internal cooling passages within the vane. Cooling is provided with ten circular passages and heat is transported by convection. The task is approached in 3D configuration. Each passage is fed with cooling air of constant parameters at the inlet. Also a constant pressure drop is assumed along the passage length. The thermal boundary conditions in passages varied with diameter and local vane temperature (passage wall temperature). The analysis is performed by means of the genetic algorithm for the optimization task and FEM for the heat transfer predictions within the component. In the present study the vane profile is taken as aerodynamically optimal and the objective of the search procedure is to find cooling structure variant that at given external conditions provides possibly low stresses and material temperature.Copyright

Results of the International Wet Steam Modeling Project

The purpose of the “International Wet Steam Modeling Project” is to review the ability of computational methods to predict condensing steam flows. The results of numerous wet-steam methods are compared with each other and with experimental data for several nozzle test cases. The spread of computed results is quite noticeable and the present paper endeavours to explain some of the reasons for this. Generally, however, the results confirm that reasonable agreement with experiment is obtained by using classical homogeneous nucleation theory corrected for non-isothermal effects, combined with Young’s droplet growth model. Some calibration of the latter is however required. The equation of state is also shown to have a significant impact on the location of the Wilson point, thus adding to the uncertainty surrounding the condensation theory. With respect to the validation of wet-steam models it is shown that some of the commonly used nozzle test cases have design deficiencies which are particularly apparent in the context of two- and three-dimensional computations. In particular, it is difficult to separate out condensation phenomena from boundary layer effects unless the nozzle geometry is carefully designed to provide near-one-dimensional flow.

Experimental and numerical validation study of the labyrinth seal configurations

This article presents a validation study of the labyrinth seal testing. Both experimental and numerical simulations are performed. Literature data focused on simple labyrinth seals are surveyed, and two different configurations widely described in literature are investigated: a labyrinth seal with two straight fins against a smooth and a honeycomb land and a seal with three straight fins against a smooth land only. For experimental testing the vacuum-feeding test rig is used, with the high-precision Hot Wire Thermoanemometry method applied for the mass flow evaluation. The dimensions of specimens described in literature are adapted to the in-house test rig conditions, meeting all the geometrical requirements mentioned by the author. The computational method is based on the Reynolds Averaged Navier Stokes scheme, with various turbulence models. The results of the simulations show good agreement with the in-house experiment, whereas some discrepancies are found compared to literature data.

Experimental and numerical study on the performance of the smooth-land labyrinth seal

In turbomachinery the secondary flow system includes flow phenomena occurring outside the main channel, where the gaseous medium performs work on blades. Secondary air distribution constitutes a very complex and closely interrelated system that affects most of the gas turbine components. One of the most important examples of the secondary flow is leakage occurring in seals, e.g. at the rotor and stator tips, on the shaft or on the sides of the blade rim. Owing to its simplicity, low price, easy maintenance and high temperature capability, the labyrinth seal is a prime sealing solution that may be selected from numerous types of sealing structures applied in turbomachinery. For this reason, an experimental study of this particular structure has been carried out. The paper presents leakage performance of the smooth-land labyrinth seal.

Convective Cooling Optimization of a Blade for a Supercritical Steam Turbine

This paper discusses the problem of blade cooling system optimization connected with Conjugate Heat Transfer (CHT) analysis for reliable thermal field prediction within a steam cooled component. Since the full CHT solution, which involves the main flow, blade material and the coolant flow domains is computationally expensive from the point of view of optimization process, it was decided to reduce the problem by fixing the boundary conditions at the blade surface and solving the task for the interior only (both solid material and coolant). Such assumption, on one hand, makes the problem computationally feasible, and on the other, provides more reliable thermal field prediction than it used to be with the empirical relationships. The analysis involves shape optimization of internal cooling passages within an airfoil. The cooling passages are modeled with a set of four Bezier splines joined together to compose a closed contour. Each passage is fed with cooling steam of constant parameters at the inlet. In the present study the airfoil profile is taken as aerodynamically optimal. The search problem is solved with evolutionary algorithm and the final configuration is to be found among the Pareto optimal cooling candidates.Copyright

Modeling of Aerodynamic Noise Using Hybrid SAS and DES Methods

The purpose of the presented studies is to compare simple and fast CFD methods based on the unsteady Reynolds-Averaged Navier-Stokes equations (uRANS) with the so called hybrid uRANS/LES methods like Detached Eddy Simulation (DES) and Scale Adaptive Simulation (SAS) implemented in the commercial code ANSYS CFX. The goal of this comparison is to find an efficient and relatively fast method for both the flow dynamic and aerodynamic noise prediction in the near and far field, which would be suitable for engineering applications. The CFD calculations were carried out using the commercial code ANSYS CFX 11. The non-reflective boundary conditions and grid stretching were used to avoid the reflections of the acoustic waves from the outer boundaries. The different boundary conditions and turbulence models were used in the calculations. For the acoustic calculations the Fast Fourier Transformation (FFT) was applied to obtain the sound spectrum. The CFD results were compared with the experimental data obtained in references.Copyright

Application of Conjugate Heat Transfer for Cooling Optimization of a Turbine Airfoil

This paper discusses the problem of airfoil cooling system optimization connected with Conjugate Heat Transfer (CHT) analysis for reliable thermal field prediction within a cooled component. Since the full CHT solution, which involves the main flow, blade material and the coolant flow domains is computationally expensive from the point of view of optimization process, it was decided to reduce the problem by fixing the boundary conditions at the blade surface and solving the task for the interior only (both solid material and coolant). Such assumption, on one hand, makes the problem computationally feasible, and on the other, provides more reliable thermal field prediction than it used to be with the empirical relationships. The analysis involves the optimization of location and size of internal cooling passages within an airfoil. Initially, cooling is provided with circular passages and heat is transported by convection. The task is approached in 3D configuration. Each passage is fed with cooling air of constant parameters at the inlet. In the present study the airfoil profile is taken as aerodynamically optimal. The optimization is done with an evolutionary algorithm within a 30 dimensional design space, composed of space coordinates and radii of cooling channels. The search is realized with a weighted single objective function, which consisted of three objectives formulated on the basis of the airfoil’s thermal field and coolant mass flow.Copyright

Coupled Analysis of Cooled Gas Turbine Blades

The paper presents solution aspects of the heat transfer modeling and fluid flow prediction of the convective cooled gas turbine blade. The heat transfer problem within the blade material is solved using finite element method whereas the flow problem employs the finite volume method. The flow field is calculated by solving the Navier-Stokes (NS) equations. The problem can be faced in two ways which are presented in this work. The first one is the uncoupled field method which does not take into consideration the interaction between the flowing medium and the blade. This way of solution is simpler and computationally cheap but has limited accuracy. The other one is the coupled field method (conjugate heat transfer CHT), which resolves iteratively the thermal interaction between the fluid and the blade material. The coupled method is much more accurate but one has to pay for it with longer computations as well as the algorithm stability control. As the fluid flow schemes are very sensitive to boundary condition changes, a fine time stepping with relaxation as well as an adequate mesh were required. The calculations showed another very important problem occurring in the analyses carried out. This is the laminar-turbulent transition which can significantly affect the accuracy of the results. The change of the flow character influences the heat exchange intensity and consequently the temperature distribution within the blade. Nevertheless, the problem is not yet satisfactorily worked out and the criteria of the laminar-turbulent transition are very difficult to build. The problem becomes simpler if the location of the transition point is known (i.e. from experimental data). On the basis of experimental data authors solved the problem of a blade cooling for both uncoupled and coupled method and different flow characters in order to obtain numerical results best matching the real phenomena.Copyright

A Numerical Study of The Heat Transfer Intensification Using High Amplitude Acoustic Waves

The current practice in the efforts aiming to improve cooling conditions is to place emphasis on the application of non-stationary flow effects, such as the unsteady jet heat transfer or the heat transfer intensification by means of a high-amplitude oscillatory motion. The research presented in this paper follows this direction. A new concept is put forward to intensify the heat transfer in the cooling channels with the use of an acoustic wave generator. The acoustic wave is generated by a properly shaped fixed cavity or group of cavities. The sound generated by the cavity is a phenomenon analysed in various publications focused on the methods of its reduction. The phenomenon is related to the feedback mechanism between the vortices flowing from the leading edge and the acoustic waves generated within the cavity. The acoustic waves are generated by the interaction between the vortices and the cavity walls. Strong instabilities can be observed within a certain range of the free flow velocities. The investigations presented in this paper are oriented towards the use of the phenomenon for the purposes of the heat transfer process intensification. The first part of the work presents the numerical model used in the analysis, as well as its validation and comparison with empirical relations. The numerical model is constructed using the commercial CFD Ansys CFX-16.0 commercial program. The next part includes determining of the relationship between the amplitude of the acoustic oscillations and the cooling conditions within the cavity. The calculations are performed for various flow conditions.