Mirko Morini

Influence of Blade Deterioration on Compressor and Turbine Performance

Gas turbine operating state determination consists of the assessment of the modification due to deterioration and fault of performance and geometric data characterizing machine components. One of the main effects of deterioration and fault is the modification of compressor and turbine performance maps. Since detailed information about actual modification of component maps is usually unavailable, many authors simulate the effects of deterioration and fault by a simple scaling of the map itself. In this paper, stage-by-stage models of the compressor and the turbine are used in order to assess the actual modification of compressor and turbine performance maps due to blade deterioration. The compressor is modeled by using generalized performance curves of each stage matched by means of a stage-stacking procedure. Each turbine stage is instead modeled as two nozzles, a fixed one (stator) and a moving one (rotor). The results obtained by simulating some of the most common causes of blade deterioration (i.e., compressor fouling, compressor mechanical damage, turbine fouling, and turbine erosion), occurring in one or more stages simultaneously, are reported in this paper. Moreover, compressor and turbine maps obtained through the stage-by-stage procedure are compared with the ones obtained by means of map scaling. The results show that the values of the scaling factors depend on the corrected rotational speed and on the load. However, since the variation in the scaling factors in the operating region close to the design corrected rotational speed is small, the use of the scaling factor as health indices can be considered acceptable for gas turbine health state determination at full load. Moreover, also the use of scaled maps in order to represent compressor and turbine behavior in deteriorated conditions close to the design corrected rotational speed can be considered acceptable.

Energy and Economic Analyses of Integrated Biogas-Fed Energy Systems

The process, which includes production, collection, carriage, and transformation of biomass into renewable fuels and then into energy (both electrical and thermal), involves a large number of decisions to select the most efficient plant layout. In order to identify the optimal solutions, models, which simulate the whole process, represent a useful and practical tool. In this paper, the energy and economic analysis of the entire process from biomass to energy production is presented. Among the different transformation processes, the thermophilic batch anaerobic digestion is considered in this paper. The analyses performed allow the comparison of the results for different scenarios characterized by different types of biomass (ensiled corn and organic fraction of municipal solid wastes), yearly mass of biomass, anaerobic digestion process parameters (number of yearly batch cycles and number of batch digesters), and type of energy systems (micro gas turbine and internal combustion engine). The results are presented in terms of classical economic indices for the investment and of producible electric and thermal energy. With respect to the economic indices, micro gas turbines allow a higher profitability than internal combustion engines, mainly because internal combustion engines require a scrubbing system to remove hydrogen sulphide from biogas. The contrary occurs with the producible electric and thermal energy. With regard to the digested substance, even if the methane yield is lower for organic fraction of municipal solid wastes than for ensiled corn, the net present values for organic fraction of municipal solid wastes are always higher than those obtained by using ensiled corn, and they are always positive, since municipal waste digestion avoids their disposal costs. The efficiency of the cogeneration process, evaluated in terms of primary energy saving index, usually shows quite high values and confirm the good capability of these systems.

Quantitative CFD Analyses of Particle Deposition on a Transonic Axial Compressor Blade: Part II — Impact Kinematics and Particle Sticking Analysis

In heavy-duty gas turbines, the micro-particles not captured by the air filtration system can cause fouling and, consequently, a performance drop of the compressor. This paper presents three-dimensional numerical simulations of the micro-particle ingestion (0–2 μm) on an axial compressor rotor carried out by means of a commercial computational fluid dynamic code. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separately from the continuous phase. The NASA Rotor 37 is considered as a case study for the numerical investigation. The compressor rotor numerical model and the discrete phase model were previously validated by the authors in the first part of this work.The kinematic characteristics (velocity and angle) of the impact of micrometric and sub-micrometric particles with the blade surface of an axial transonic compressor are shown. The blade zones affected by particle impact were extensively analyzed and reported in the first part of this work, forming the starting point for the analyses shown in this paper.The kinematic analysis showed a high tendency of particle adhesion on the suction side, especially for the particles with a diameter equal to 0.25 μm. Fluid dynamic phenomena and airfoil shape play a key role regarding particle impact velocity and angle.This work has the goal of combining, for the first time, the kinematic characteristics of particle impact on the blade with fouling phenomenon by the use of a quantity called sticking probability adopted from literature.From these analyses, some guidelines for a proper management of the power plant (in terms of filtration and washing strategies) are highlighted.Copyright

Cross Validation of Multistage Compressor Map Generation by Means of Computational Fluid Dynamics and Stage-Stacking Techniques

Gas turbine operating state determination consists of the assessment of the modification, due to deterioration and fault, of performance and geometric data characterizing machine components. One of the main effects of deterioration and fault is the modification of compressor and turbine performance maps. In this paper, three-dimensional numerical simulations of a multistage axial compressor are carried out. As a case study, the axial sections (i.e. the first six stages) of the Allison 250-C18 axial-centrifugal compressor are considered for the numerical investigation. Simulations are performed by means of a commercial computational fluid dynamic code. A multistage numerical model is set up and validated against the experimental data, gathered from an in-house test rig. Computed performance maps and main flow field features show fairly good agreement with the experimental data. The model is then used to cross-validate the results of zero-dimensional stage-stacking procedures and the stage maps obtained by means of a multistage CFD calculation (i.e. to evaluate the mutual consistency of the two methods for the generation of multistage compressor maps). The stage-stacking procedure results adequately fit the behavior of the multistage compressor.Copyright

An Innovative Inlet Air Cooling System for IGCC Power Augmentation: Part III — Computational Fluid Dynamic Analysis of Syngas Combustion in Nitrogen-Enriched Air

In recent years, an innovative system for power augmentation has been presented by the authors. The system is based on gas turbine inlet air cooling by means of liquid nitrogen sprayers. This system is not characterized by the limits of water evaporative cooling (i.e. lower temperature limited by air saturation) and refrigeration cooling (i.e. effectiveness limited by pressure drop in the heat exchangers), but the injection of a large amount of liquid nitrogen at gas turbine inlet section can be disputable.In fact, the air composition changes, though not considerably, after nitrogen injection. The oxygen content always seems high enough to allow a regular combustion. In any case, local effects should be further investigated.In this paper, the effect of the increase in nitrogen molar fraction of combustion air is evaluated. A micro gas turbine combustion chamber geometry (i.e. a reverse flow tubular combustor) is taken into consideration since its model has been widely validated by the authors. The analyses are performed by considering two different fuels: methane (which is the design fuel) and syngas. The results are compared in terms of overall performance (e.g. TIT, pollutant emissions) and local distributions (e.g. flow fields, flame shape and position).Copyright

Performance Evaluation of Non-Uniformly Fouled Axial Compressor Stages by Means of Computational Fluid Dynamic Analyses

In this paper, three-dimensional numerical simulations are carried out to evaluate the effect of fouling on an axial compressor stage. A numerical model of the NASA Stage 37, validated in previous papers of the same authors against experimental data available from literature, is used as a case study.The occurrence of fouling is simulated by imposing different spanwise distributions of surface roughness, in order to analyze its effect on compressor performance. To this aim, both the stage performance maps of the fouled compressor and the spanwise distribution of work and losses are analyzed and discussed. Moreover, the definition of an averaged roughness parameter is suggested, to characterize the different roughness distributions.The results show that the drop of overall performance can actually be predicted by means of the numerical model. Moreover, detailed information about fluid-dynamic phenomena can be analyzed on the basis of the actual distribution of surface roughness on rotor blades.Copyright

Quantitative CFD Analyses of Particle Deposition on an Axial Compressor Blade: Part I — Particle Zones Impact

Solid particle ingestion is one of the principal degradation mechanisms in the turbine and compressor sections of gas turbines. In particular, in industrial applications, the micro-particles not captured by the air filtration system cause fouling and, consequently, a performance drop of the compressor. This paper presents three-dimensional numerical simulations of the micro-particle ingestion (0–2 μm) on an axial compressor rotor carried out by means of a commercial computational fluid dynamic code. Particles of this size can follow the main air flow with relatively little slip, while being impacted by flow turbulence. It is of great interest to the industry to determine which areas of the compressor airfoils are impacted by these small particles.Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separate from the continuous phase. Then, the NASA Rotor 37 is considered as a case study for the numerical investigation. The compressor rotor numerical model and the discrete phase treatment have been validated against the experimental and numerical data available in literature. The number of particles, sizes, and concentrations are specified in order to perform a quantitative analysis of the particle impact on the blade surface.The results show that micro-particles tend to follow the flow by impacting at full span with an higher impact concentration on the pressure side. The suction side is affected only by the impact of the smaller particles (up to 1 μm). Particular fluid-dynamic phenomena such as separation, stagnation point and tip leakage vortex strongly influence the impact location of the particles.Copyright