Massimiliano Maritano

Influence of Purge Flow Injection Angle on the Aerothermal Performance of a Rotor Blade Cascade

This paper is focused on the influence of stator-rotor purge flow injection angle on the aerodynamic and thermal performance of a rotor blade cascade. Tests were performed in a seven-blade cascade of a high-pressure gas turbine rotor at low Mach number (Ma2is = 0.3) under different blowing conditions. A number of fins were installed inside the upstream slot to simulate the effect of rotation on the seal flow exiting the gap in a linear cascade environment. The resulting coolant flow is ejected with the correct angle in the tangential direction. Purge flow injection angle and blowing conditions were changed in order to identify the best configuration in terms of end wall thermal protection and secondary flows reduction. The 3D flow field was surveyed by traversing a five-hole miniaturized pressure probe in a downstream plane. Secondary flow velocities, loss coefficient, and vorticity distributions are presented for the most significant test conditions. Film cooling effectiveness distributions on the platform were obtained by thermochromic liquid crystals (TLC) technique. Results show that purge flow injection angle has an impact on secondary flows development and, thus, on the end wall thermal protection, especially at high injection rates. Passage vortex is enhanced by a negative injection angle, which simulates the real counter rotating purge flow direction.

The Impact of Gas Modeling in the Numerical Analysis of a Multistage Gas Turbine

In this work a numerical investigation of a four stage heavy-duty gas turbine is presented. Fully three-dimensional, multistage, Navier-Stokes analyses are carried out to predict the overall turbine performance. Coolant injections, cavity purge flows, and leakage flows are included in the turbine modeling by means of suitable wall boundary conditions. The main objective is the evaluation of the impact of gas modeling on the prediction of the stage and turbine performance parameters. To this end, four different gas models were used: three models are based on the perfect gas assumption with different values of constant c p , and the fourth is a real gas model which accounts for thermodynamic gas properties variations with temperature and mean fuel/air ratio distribution in the through-flow direction. For the real gas computations, a numerical model is used which is based on the use of gas property tables, and exploits a local fitting of gas data to compute thermodynamic properties. Experimental measurements are available for comparison purposes in terms of static pressure values at the inlet/outlet of each row and total temperature at the turbine exit.

Aero-Thermal Performance of a Rotor Blade Cascade With Stator-Rotor Seal Purge Flow

The present paper investigates the effects of purge flow from a stator-rotor seal gap on the aerodynamic and thermal performance of a rotor blade cascade. Particular attention is paid to thermal results in the leading edge area that is typically difficult to protect. Experimental tests have been performed on a seven-blade cascade of a high-pressure rotor stage of a real gas turbine at low Mach number (Ma2is = 0.3). To simulate the rotational effect in a linear cascade environment, a number of inclined fins have been installed inside the stator-rotor gap, making the coolant flow to exit with the right tangential velocity component. Tests have been carried out at different blowing conditions, with mass flow rate ratios up to 2.0%. Aerodynamic effects of purge flow on secondary flow structures were surveyed by traversing a 5-hole miniaturized pressure probe in a plane 0.08cax downstream of the trailing edge. Film cooling effectiveness distributions on the end wall platform were obtained by using Thermochromic Liquid Crystals technique. Results allowed to investigate the effect of purge flow injection from the upstream gap on the secondary flows development and on the thermal protection capability. Purge flow injection of 1.0% reduced secondary flow losses and was found to effectively protect the front end wall region, up to about 0.5cax downstream of the leading edge. Increasing the purge flow up to 1.5%–2.0% provided a better thermal protection not only stream wise, but also in the region close to the leading edge because of the weakened washing activity of the horseshoe vortex.Copyright

Computational Predictions of Aero-Thermal Performance of a Turbine Filleted Blade Cascade With Endwall Film Cooling

In this study computational fluid dynamic simulations of a turbine blade with endwall film cooling were compared to measurements of both aerodynamic and thermal performance. The experimental data were collected at low Mach number (Ma2is = 0.3) in a linear cascade arrangement with 7 blades which geometry is typical of first stage high pressure turbine. A junction between the blade hub and the platform is provided by a 3D fillet. Coolant is injected through ten cylindrical holes distributed along the blade pressure side. Coolant to mainstream mass flow ratio was set to assure an inlet blowing ratio of M1 = 2.4 and M1 = 3.2. The simulations were carried out using the Shear Stress Transport (SST) k-turbulence model. Numerical predictions were compared against experimentally measured secondary flows and endwall film cooling effectiveness, at different injection conditions. Simulation results agreed with the experiments for what concerns the general shape and the location of secondary flows. However, some limitations in the modeling were highlighted when going into the details of loss computation and vortex structure. Predictions overestimated both secondary and midspan blade wake losses. Moreover, the effect of the fillet on the aerodynamic flow features was not fully captured. Predicted film cooling results showed the sweeping of coolant across the passage in agreement with experiments even though jets persistency was higher than that measured. Levels of adiabatic effectiveness were generally well simulated.

Numerical Investigation on the Influence of the Fillet on Film Cooling Rotor Blades in Heavy Duty Gas Turbines With an Object-Oriented CFD Code

The present paper examines the numerical simulation of the effects of film wall cooling on rotor blades in a high-pressure-ratio axial turbine. Special attention is given to the differently shaped geometries of the fillet at the blade endwall and their influence on secondary flows, since the fillet is often neglected in CFD calculations in order to minimize the effort in grid generation.Simulations were conducted using both sharp and radius edge fillet configurations to investigate the effects on film cooling and secondary flows. For this purpose all simulations were performed using a modified in-house 3D RANS solver based on an object-oriented open-source library. The results were compared against experimental measurements in terms of local quantities such as aerodynamic losses and adiabatic effectiveness.Copyright

Development and Validation of an Object-Oriented Code Implementing an Enhanced Radiative Joined MBL-Zonal Method Technique

Gas turbines are the most widely employed high power prime movers for energy production and propulsion; their success is based on high power density, high reliability and low pollutant emissions. Due to the increasing performance request of modern gas turbines, combustion chambers and, more in general, turbine components are subjected to increasingly high thermal loads, due to both convection and radiation between solid walls and internal fluid. Computational Fluid Dynamics (CFD) tools are typically employed to reproduce these phenomena: commercial codes provide tools for both the heat transfer methods, but the radiation analysis sometimes could represent a great increase in the computational load; for this reason, it is a widespread industrial practice to avoid direct simulation of radiative phenomena during simulations, confining it during the post-processing activity. A typical industrial approach relies on the so-called Zonal Method, which guarantees a good compromise between accuracy of results and computational load. In a previous work, an innovative method for radiative thermal load evaluation has been presented by the authors, which is based on a joined Zonal Method-Mean Beam Length (MBL) approach: it enables a great reduction in time consumption by means of an appropriate Artificial Neural Network, but its usage is limited to hexahedral structured grids, which reduces its application to relatively simple geometries. In this paper, the method previously mentioned has been extended to unstructured tetrahedral grids. The procedure developed has been implemented in an object-oriented code by means of an open-source library: great advantages have been obtained both in the implementation, which results to be simpler, making any future modifications faster and intuitive, and in the application field, being extended to almost any kind of geometry. The code has been validated on literature test cases providing a good agreement between numerical and experimental results. Moreover, an industrial application has been described: it concerns the evaluation of the radiative heat transfer on the shells of an industrial gas turbine combustion chamber. Results are presented and discussed.Copyright

Influence of Coolant Flow Rate on Aero-Thermal Performance of a Rotor Blade Cascade With Endwall Film Cooling

This paper investigates the influence of coolant injection on the aerodynamic and thermal performance of a rotor blade cascade with endwall film cooling. A 7 blade cascade of a high-pressure-rotor stage of a real gas turbine has been tested in a low speed wind tunnel for linear cascades. Coolant is injected through ten cylindrical holes distributed along the blade pressure side. Tests have been preliminarily carried out at low Mach number (Ma2is=0.3). Coolant-to-mainstream mass flow ratio has been varied in a range of values corresponding to inlet blowing ratios M1 = 0 – 4.0. Secondary flows have been surveyed by traversing a 5-hole miniaturized aerodynamic probe in two downstream planes. Local and overall mixed-out secondary loss coefficient and vorticity distributions have been calculated from measured data. The thermal behaviour has been also analysed by using Thermochromic Liquid Crystals technique, so to obtain film cooling effectiveness distributions. All this information, including overall loss production for variable injection conditions, allow to draw a comprehensive picture of the aero-thermal flow field in the endwall region of a high pressure rotor blade cascade.

A Joined MBL-Zonal Method Technique for Evaluating Radiative Thermal Loads Into Combustion Chambers of Industrial Gas Turbines

Thermal radiation is typically one of the most important phenomenon to be taken into account in the evaluation of combustor walls thermal loads due to the high temperatures reached into them. A classical approach is based on the so called Zonal Method, originally developed by Hottel and Sarofim (1967), and actually widely employed in the industrial environment. Even if its accuracy has been largely demonstrated, its efficiency is affected by computational costly solution of 4 th – 6 th fold integrals constituting the DEAs. A direct integration is usually employed, subsequently smoothing the results in order to obey the conservation constraints. The last decades have seen a growing interest on developing new techniques able to simplify these time consuming direct numerical integrations. Among them one of the most promising approaches has been recently introduced by Yuen (2008) which is based on the classic Mean Beam Length concept. The emittance (absorptance) coefficients of the radiating (receiving) gas volume zones of cubic shape are treated as those of a grey gas filled hemisphere. According to Yuen (2008), a correlative expression has been employed for evaluating the MBL corresponding to each single volume zone. In the present work its application has been extended to more complex zone shapes by means of an Artificial Neural Network trained on a properly selected geometry database. In this way the DEA integral folds can be all reduced to the 4 th order, and, employing well known geometrical techniques (Walton, 2002), can be further decreased to lower order integrals. The proposed model has been compared with 3D benchmark test cases available in literature: the accuracy has been tested against the results of DTM, FVM and classical Zonal Method. Moreover an industrial application is shown. The geometry of the AE94.2 gas turbine combustion chamber has been considered; the gas mixture has been treated as a non-grey gas using the well known Weighted Sum of Gray Gases (WSGG) model. In comparison with the classical zonal method approach, the efficiency of the proposed one demonstrates the possibility of a zone refinement enabling a more accurate evaluation of radiative thermal loads at the same computational cost. Results are presented and discussed.© 2011 ASME