Modeling of Particle Trajectory and Erosion of Large Rotor Blades

When operating in hostile environments, engines components are facing a serious problem of erosion, leading to a drastic drop in aerodynamic performance and life-cycle. This paper outlines the modeling and simulation of particle trajectory and erosion induced by sand particles. The governing equations of particle dynamics through the moving of large rotor blades are introduced and solved separately from the flow field by using our in-house particle tracking code based on the finite element method. As the locations of impacts are predicted, the erosion is assessed by semiempirical correlations in terms of impact conditions and particle and target surface characteristics. The results of these computations carried out for different concentrations of suspended dust (sand) cloud generated at takeoff conditions reveal the main areas of impacts with high rates of erosion seen over a large strip from the blade suction side, around the leading edge and the pressure side of blade. The assessment of the blade geometry deterioration reveals that the upper corner of blade suffers from an intense erosion wear

Nusselt Correlations in a Trailing Edge Cooling System with Long Pedestals and Ribs

AbstractDetailed TLC measurements have been carried out to estimate the heat transfer coefficient in stationary conditions under high Reynolds numbers in a trailing edge cooling system of a high pressure gas turbine blade. The investigated geometry consists of a 30:1 PMMA scaled model reproducing the typical wedge-shaped discharge duct of a trailing edge cooling system with one row of 7 enlarged pedestals. The section of the channel upstream the pedestal region is used to guide the airflow from the radial hub inlet to the tangential trailing edge outlet; in this section three different surfaces have been studied: one is smooth and the other two are ribbed with +60° and -60° angled ribs respect to the radial direction. This work focuses on the pedestal outlet section, by giving a correlation of the variation of the Nusselt number as a function of the Reynolds number, from 10000 to 40000, in the different inter-pedestal regions along the radial direction. These correlations give the regionally averaged heat transfer coefficients, from the hub to the tip of the model for both smooth and ribbed cases. The interest of these results is the use for the design of the trailing edge blade cooling systems, under the investigated Reynolds number range, that it is the typical case of the industrial application

Turbomachinery performance degradation due to erosion effect

Erosion of gas turbines operating in sandy or dusty environments can result in serious damage to the engine components, particularly the compressor unit. This phenomenon is a result of the ingestion of the sand particles into the engine and their consequent abrasive impacts on the blade surfaces. In order to understand the mechanism of sand ingestion and the resulting performance degradation, a general methodology has been developed for predicting the trajectories of particles, the erosion rates and blade profile changes, with predictive capabilities for performance degradations within more general configurations of turbomachines. This methodology was applied to an axial fan with upstream guide vanes (contra whirl) and was supported by experimental results. The numerical models for calculating the particle trajectory are based on the Lagrangian tracking technique and the eddy lifetime concept. The turbulence effect is assumed to prevail as long as the particle eddy interaction time is less than the eddy lifetime, and the displacement of a particle relative to the eddy is less than the eddy length. The flow field was solved separately using the Navier-Stokes finite volume flow solver " TASCflow " commercially available from ASC. The governing equations of the particle motion are solved using the Runge-Kutta Fehlberg technique. The tracking of particles and their locations is based on a finite element interpolation method. The developed Fortran code for predicting particle trajectory and erosion due to particle impact accounts for different types of boundary conditions and handles different frames of reference. The fragmentation of particles after rebound was also implemented. The number of particles seeded upstream of the IGV blades can be determined either by a user defined concentration profile or by a measured concentration profile. Also, particles can be seeded separately in a group at a release position. In the present study, the concentration profile and the initial particle velocity and angle of particle spread were determined from a laser transit anemometer. Two types of particles were used, a narrow size bandwidth (150-300micron) quartz particle and MIL-E5007E quartz particle, both of which have a normal distribution. The global rate of erosion, the reduced mass of blades and the changes of the blade geometry were predicted and compared with experimental results at different concentration levels. The baseline axial fan characteristics were measured at different mass flow conditions at a constant speed of rotation. To assess the effects of erosion, the characteristic measurement was repeated after each step of sand ingestion. The predicted aerodynamic performance; adiabatic efficiency, pressure rise coefficient and stall margin before and after erosion degradation were also determined from a developed Fortran program, which is basically a mean line method that uses advanced correlations for aerodynamic losses. Prediction of the particle trajectories show that high numbers of impacts (and maximum erosion) occurred near leading edge and tip region, which were also borne out by locally injected sand tests. The global rate of erosion and the consequent changes of the blade geometry were also predicted and compared with experimental results. The erosion pattern at high concentration of MIL-E5007E sand particles depicts net loss of material over the leading edge and the tip corner. The tip clearance increased markedly with a rounding of blade leading edge, which is the main cause of the decrease in efficiency, pressure rise, and surge margin. A parametric study with turbulence and fragmentation effects show that both parameters can influence the erosion rate and blade geometry deterioration. The results of the aerodynamic performance simulation using mean line method, which includes an erosion fault model, show good agreement with experimental results

Characterization of Flow Interactions in a One-Stage Shrouded Axial Turbine

The aim of this paper is to characterize the steady and unsteady flow interactions through a one-stage high-pressure (hp) shrouded axial turbine with a tip cavity. The vane and blade passages were reduced based on the scaling technique, and the domains of compromise were identified and used in the flow computations. The flow structures are mainly in the form of vanes’ wakes and vortices inducing circumferential distortions and interacting with the rotor blades. Fast Fourier transform (FFT) of the static pressure fluctuations recorded at the selected points and lines through the turbine stage revealed high unsteadiness characterized by a space-time periodic behavior, and described by the double Fourier decomposition. The vane-rotor interactions (VRI) appeared in the form of a potential flow field about the blades extending both upstream and downstream and correlated with the rotational speed. The other sources of unsteadiness are induced in the rotor blades by the vanes’ wakes and referred to as the wake interaction, in addition to the secondary flows and vortices in endwall regions

GT2008-50339 COMPUTATION OF THE FLOW FIELD OF TRANSONIC AXIAL COMPRESSOR ROTOR BY STEADY ARBITRARY LAGRANGIAN EULERIAN FORMULATION

ABSTRACT This paper presents a multi-block solver dealing with an inviscid three dimensional compressible flow through a transonic compressor blading. For efficient computations of the 3D time dependant Euler equations, this solver that we have developed has been cast within a stationary ALE 'Arbitrary Lagrangian Eulerian'. The main contribution of this paper is by consolidating this ALE formulation, to alleviate the shortcomings linked to rotation effects and the mixed relative subsonic -supersonic inlet flow conditions, which are now simply implemented through an absolute subsonic flow velocity. The finite volume based solver is using the central differencing scheme known as JST (Jameson-Schmidt-Turkel). The explicit multistage Runge-Kutta algorithm is used as a pseudo time marching to the steady-state, coupled with two convergence accelerating techniques; the variable local timestepping and the implicit residual smoothing procedure. The adaptive implicit residual smoothing has extended the stability range of this explicit scheme, and proved to be successful in accelerating the rate of convergence. This code is currently being extended to include viscous effects, where fluxes are discretized based on Green's theorem. To support this solver, an H type grid generator based on algebraic and elliptic methods has been developed. The segmentation of the complete domain into smaller blocks has provided full topological and geometrical flexibilities. The code was used to compute the flow field of a transonic axial compressor NASA rotor 37, and comparisons between the calculations and some available experimental data under the design speed and part speed, show qualitatively good agreement

Characterization of a Twin-Entry Radial Turbine under Pulsatile Flow Condition

In automotive applications radial gas turbines are commonly fitted with a twin-entry volute connected to a divided exhaust manifold, ensuring a better scavenge process owing to less interference between engines’ cylinders. This paper is concerned with the study of the unsteady performances related to the pulsating flows of a twin-entry radial turbine in engine-like conditions and the hysteresis-like behaviour during the pulses period. The results show that the aerodynamic performances deviate noticeably from the steady state and depend mainly on the time shifting between the actual output power and the isentropic power, which is distantly related to the apparent length. The maximum of efficiency and output shaft power are accompanied by low entropy generation through the shroud entry side, and their instantaneous behaviours tend to follow mainly the inlet total pressure curve. As revealed a billow is created by the interaction between the main flow and the infiltrated flow, affecting the flow incidence at rotor entry and producing high losses

Characterization of component interactions in two-stage axial turbine

This study concerns the characterization of both the steady and unsteady flows and the analysis of stator/rotor interactions of a two-stage axial turbine. The predicted aerodynamic performances show noticeable differences when simulating the turbine stages simultaneously or separately. By considering the multi-blade per row and the scaling technique, the Computational fluid dynamics (CFD) produced better results concerning the effect of pitchwise positions between vanes and blades. The recorded pressure fluctuations exhibit a high unsteadiness characterized by a space–time periodicity described by a double Fourier decomposition. The Fast Fourier Transform FFT analysis of the static pressure fluctuations recorded at different interfaces reveals the existence of principal harmonics and their multiples, and each lobed structure of pressure wave corresponds to the number of vane/blade count. The potential effect is seen to propagate both upstream and downstream of each blade row and becomes accentuated at low mass flow rates. Between vanes and blades, the potential effect is seen to dominate the quasi totality of blade span, while downstream the blades this effect seems to dominate from hub to mid span. Near the shroud the prevailing effect is rather linked to the blade tip flow structure

Simulations of Steady Cavitating Flow in a Small Francis Turbine

The turbulent flow through a small horizontal Francis turbine is solved by means of Ansys-CFX at different operating points, with the determination of the hydrodynamic performance and the best efficiency point. The flow structures at different regimes reveal a large flow eddy in the runner and a swirl in the draft tube. The use of the mixture model for the cavity/liquid two-phase flow allowed studying the influence of cavitation on the hydrodynamic performance and revealed cavitation pockets near the trailing edge of the runner and a cavitation vortex rope in the draft tube. By maintaining a constant dimensionless head and a distributor vane opening while gradually increasing the cavitation number, the output power and efficiency reached a critical point and then had begun to stabilize. The cavitation number corresponding to the safety margin of cavitation is also predicted for this hydraulic turbine