Porosity Driven Approaches to Model Fouling Effects on Flow Field

2019 ◽  
Author(s):  
Nicola Casari ◽  
Alessio Suman ◽  
Michele Pinelli
Keyword(s):  
Gas Turbines ◽  
Computational Grid ◽  
Comprehensive Analysis ◽  
Solid Particles ◽  
Heavy Duty ◽  
Air Contamination ◽  
Performance Reduction ◽  
Main Effects ◽  
Over Time ◽  
Large Deposits

Abstract Air contamination by solid particles represents a real hazard for compressors for both heavy-duty and aero-propulsion gas turbines. Particles impacting the inner surfaces of the machine can stick to such surfaces or erode them. The presence of deposits entails the reduction in performance of the machinery. As the severity of the problem increases, the performance reduction can become so big to demand engine shut-down and off-line washing. Numerical modeling is one of the techniques employed for tackling the fouling problem. In this work, an innovative procedure is proposed in order to evaluate the losses and the variation in the fluid flow due to the deposits. Specifically, as the deposit grows, it is assumed it forms a porous medium attached to the wall. The porosity of this zone (related to the packing of the particles and to the amount of particles that sticks in to a zone) is responsible for the deposition-induced losses. Different approaches to compute such losses are proposed and discussed. By using this methodology, the two main effects of fouling (variation in roughness and in shape of the airfoil) can be easily included in a comprehensive analysis of the variation of the performance of the compressor over time. Furthermore, this approach overcomes the difficulties that may arise by using a mesh morphing technique. The computational grid is not modified and thus its quality is retained, without remeshing requirements, even for large deposits.

Porosity-Driven Approaches to Model Fouling Effects on Flow Field

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Nicola Casari ◽  
Alessio Suman ◽  
Michele Pinelli
Keyword(s):  
Gas Turbines ◽  
Computational Grid ◽  
Comprehensive Analysis ◽  
Solid Particles ◽  
Heavy Duty ◽  
Air Contamination ◽  
Performance Reduction ◽  
Main Effects ◽  
Number Of Particles ◽  
Large Deposits

Abstract Air contamination by solid particles represents a real hazard for compressors for both heavy-duty and aeropropulsion gas turbines. Particles impacting the inner surfaces of the machine can stick to such surfaces or erode them. The presence of deposits entails a reduction in performance, in a phenomenon commonly referred to as fouling. As the severity of the problem increases, the performance reduction can become so big to demand engine shut down and offline washing. Numerical modeling is one of the techniques employed for tackling the fouling problem. In this work, an innovative procedure is proposed to evaluate the losses and the variation in the fluid flow due to the deposits. Specifically, as the deposit grows, it is assumed that it forms a porous medium attached to the wall. The porosity of this zone (related to the packing of the particles and to the number of particles that sticks to that portion of the wall) is responsible for the deposition-induced losses. Different approaches to compute such losses are proposed and discussed. By using this methodology, the two main effects of fouling (variation in roughness and in shape of the airfoil) can be easily included in a comprehensive analysis of the variation of the performance of the compressor over time. Furthermore, this approach overcomes the difficulties that may arise by using a mesh morphing technique. The computational grid is not modified, and thus, its quality is retained, without remeshing requirements, even for large deposits.

An Innovative Approach Towards Fouling Modeling: Microscale Deposition Pattern and its Effect on the Flow Field

2018 ◽  
Author(s):  
Nicola Casari ◽  
Michele Pinelli ◽  
Alessio Suman
Keyword(s):  
Gas Turbines ◽  
Comprehensive Analysis ◽  
Degradation Mechanisms ◽  
Heavy Duty ◽  
Deposition Pattern ◽  
Mesh Morphing ◽  
Extra Effort ◽  
Wall Interaction ◽  
Particle Ingestion ◽  
Large Deposits

Solid particle ingestion is one of the main compressor degradation mechanisms for both heavy-duty and aero-propulsion gas turbines. Particles impacting the inner surfaces of the machine can stick there forming deposits. The presence of such deposits reflects on the reduction in performance of the machinery. Over last years, several methods have been developed in order to study the problem from the numerical standpoint. Examples of these techniques are the mesh morphing approach and the added-roughness-and-thickness method. In this work, an innovative procedure is proposed in order to evaluate the losses and the variation in the fluid flow due to the deposits. Particularly, an algorithm capable of determining the microscale deposition pattern has been developed. By using this methodology, a comprehensive analysis of the variation of the performance of the compressor over time can be carried out. The deposition severity and the subsequent roughness variation can be kept into account in a very detailed and precise fashion. Furthermore, this approach overcomes the difficulties that may arise by using a mesh morphing technique. The computational grid is not modified and thus its quality is retained, without re-meshing requirements, even for large deposits. The local roughness variation is accounted for without extra-effort. The procedure developed, shown here in deposition problems, can be easily extended to erosion or even icing problems. The only parameter to be changed is the model that takes care of the particle-wall interaction, using an erosion rather than an icing law.

On Deposit Sintering and Detachment From Gas Turbines

2018 ◽  
Author(s):  
Nicola Casari ◽  
Michele Pinelli ◽  
Alessio Suman ◽  
Luca di Mare ◽  
Francesco Montomoli
Keyword(s):  
Gas Turbines ◽  
Solid Particles ◽  
Sintering Process ◽  
Centrifugal Forces ◽  
Single Particles ◽  
Sintering Time ◽  
Applied Forces ◽  
The Stability ◽  
Mesh Technique ◽  
Over Time

Solid particles ingestion can deteriorate performance and stability of gas turbines through the build-up of deposits on the aerofoils. In some cases, the effect is sufficient to require an engine shut-down or to cause a failure. The fouling phenomenon can be characterized by two different phases: particle sticking and deposit evolution. The sticking process of an impinging particle has been deeply studied with several models available in the literature, both deterministic and stochastic. A less investigated phase is the the evolution of the deposit over time. A deposit is subjected to several forces that either tend to make it sticking to the surface or to detach from it. In the hot section of the gas turbine, the forces that act on the build-up tending to make it to adhere to the surface can be traced back to the van der Waals forces and, possibly capillary force if a certain amount of liquid phase is present. On the other hand, the detaching mechanism is related to the component investigated: if the particle is deposited on a vane, the drag and the shearing force are the only forces that tend to detach the particle, if a rotor blade is investigated, the centrifugal forces must be considered as well. On top of that, the deposit evolves over time in what is called sintering. During this process, the single particles deposited can melt together forming necks. If the temperature is sufficiently high, these necks increase in size until the former pores among particles are completely filled. This process is of paramount importance if the effect of the applied forces on the deposit needs to be investigated. The amount of material detached is indeed strongly dependent on the tension exchanged within various layers that constitute the build-up. This article focuses on the prediction of the build-up evolution on an HPT nozzle. The sintering process is modeled and related to the resisting strength of the deposit: an increasing sintering time reduces the deposit porosity and thus increase its strength. In order to monitor the stability of the deposit, the balance among detaching and attaching forces is carried out. The evolution of the vane shape is taken into account by using a moving mesh technique.

scholarly journals Investigation of Failure in Gas Turbines: Part 2 — Engineering and Metallographic Aspects of Failure Investigation

1993 ◽  
Author(s):  
Robert E. Dundas
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Heavy Duty ◽  
Metallographic Examination ◽  
Fracture Surfaces ◽  
Failure Investigation ◽  
Materials Used ◽  
Component Failures

This paper opens with a discussion of the various mechanisms of cracking and fracture encountered in gas turbine failures, and discusses the use of metallographic examination of crack and fracture surfaces. The various types of materials used in the major components of heavy-duty industrial and aeroderivative gas turbines are tabulated. A collection of macroscopic and microscopic fractographs of the various mechanisms of failure in gas turbine components is then presented for reference in failure investigation. A discussion of compressor damage due to surge, as well as some overall observations on component failures, follows. Finally, a listing of the most likely types of failure of the various major components is given.

Development and Validation of a Three-Dimensional Multiphase Flow CFD Analysis for Journal Bearings in Steam and Heavy Duty Gas Turbines

2012 ◽  
Author(s):  
Stephan Uhkoetter ◽  
Stefan aus der Wiesche ◽  
Michael Kursch ◽  
Christian Beck
Keyword(s):  
Experimental Data ◽  
Multiphase Flow ◽  
Gas Turbines ◽  
High Speed ◽  
Three Dimensional ◽  
Air Entrainment ◽  
Journal Bearings ◽  
Heavy Duty ◽  
Present Contribution ◽  
Two Phase

The traditional method for hydrodynamic journal bearing analysis usually applies the lubrication theory based on the Reynolds equation and suitable empirical modifications to cover turbulence, heat transfer, and cavitation. In cases of complex bearing geometries for steam and heavy-duty gas turbines this approach has its obvious restrictions in regard to detail flow recirculation, mixing, mass balance, and filling level phenomena. These limitations could be circumvented by applying a computational fluid dynamics (CFD) approach resting closer to the fundamental physical laws. The present contribution reports about the state of the art of such a fully three-dimensional multiphase-flow CFD approach including cavitation and air entrainment for high-speed turbo-machinery journal bearings. It has been developed and validated using experimental data. Due to the high ambient shear rates in bearings, the multiphase-flow model for journal bearings requires substantial modifications in comparison to common two-phase flow simulations. Based on experimental data, it is found, that particular cavitation phenomena are essential for the understanding of steam and heavy-duty type gas turbine journal bearings.

Dynamic Simulation of Full Start-Up Procedure of Heavy Duty Gas Turbines

2001 ◽  
Author(s):  
J. H. Kim ◽  
T. W. Song ◽  
T. S. Kim ◽  
S. T. Ro
Keyword(s):  
Gas Turbines ◽  
Guide Vane ◽  
Inlet Guide Vane ◽  
Stable Operation ◽  
Heavy Duty ◽  
Operating Characteristics ◽  
Fully Implicit ◽  
Start Up ◽  
Full Speed ◽  
Stage Characteristic

A simulation program for transient analysis of the start-up procedure of heavy duty gas turbines for power generation has been constructed. Unsteady one-dimensional conservation equations are used and equation sets are solved numerically using a fully implicit method. A modified stage-stacking method has been adopted to estimate the operation of the compressor. Compressor stages are grouped into three categories (front, middle, rear), to which three different stage characteristic curves are applied in order to consider the different low-speed operating characteristics. Representative start-up sequences were adopted. The dynamic behavior of a representative heavy duty gas turbine was simulated for a full start-up procedure from zero to full speed. Simulated results matched the field data and confirmed unique characteristics such as the self-sustaining and the possibility of rear-stage choking at low speeds. Effects of the estimated schedules on the start-up characteristics were also investigated. Special attention was paid to the effects of modulating the variable inlet guide vane on start-up characteristics, which play a key role in the stable operation of gas turbines.

The Use of Electrostatic Charge Measurements as an Early Warning of Distress in Heavy-Duty Gas Turbines

2001 ◽  
Author(s):  
G. L. Lapini ◽  
M. Zippo ◽  
G. Tirone
Keyword(s):  
Monitoring System ◽  
Early Warning ◽  
Gas Turbines ◽  
Electrostatic Charge ◽  
Electric Utility ◽  
Operating Conditions ◽  
System Response ◽  
Jet Engines ◽  
Heavy Duty ◽  
Demonstration Program

The idea of measuring the electrostatic charge associated with the debris contained in the exhaust gases of a gas turbine (sometimes named EDMS, Engine Debris Monitoring System, or EEMS, Electrostatic Engine Monitoring System) has been demonstrated by several authors as an interesting diagnostic tool for the early warning of possible internal distresses (rubs, coating wear, hot spots in combustors, improper combustion, etc.) especially for jet engines or aeroderivative gas turbines. While potentially applicable to machines of larger size, the possibility of transferring this monitoring technology to heavy-duty gas turbines, which have exhaust ducts much bigger in size and different operating conditions, should be demonstrated. The authors present a synthesis of their experience and of the most significant data collected during a demonstration program performed on behalf of ENEL, the main Italian electric utility. The purpose of this program was to test this concept in real operating conditions on large turbines, and hence to evaluate the influence of the operating conditions on the system response and to assess its sensitivity to possible distresses. A good amount of testing has been performed, during this program, both on a full scale combustion rig, and on two machines rated at about 120 MW, during their normal and purposely perturbed operating conditions in a power plant. The authors, on the basis of the encouraging results obtained to date, comment on the work still required to bring this technology to full maturity.

Application of Forecasting Methodologies to Predict Gas Turbine Behavior Over Time

2011 ◽  
Author(s):  
A. Cavarzere ◽  
M. Venturini
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Current Trend ◽  
Performance Limit ◽  
Industrial Systems ◽  
Forecasting Method ◽  
Double Exponential ◽  
The Future ◽  
Double Exponential Smoothing ◽  
Over Time

The growing need to increase the competitiveness of industrial systems continuously requires a reduction of maintenance costs, without compromising safe plant operation. Therefore, forecasting the future behavior of a system allows planning maintenance actions and saving costs, because unexpected stops can be avoided. In this paper, four different methodologies are applied to predict gas turbine behavior over time: Linear and Non Linear Regression, One Parameter Double Exponential Smoothing, Baesyan Forecasting Method and Kalman Filter. The four methodologies are used to provide a prediction of the time when a performance limit will be exceeded in the future, as a function of the current trend of the considered parameter. The application considers different scenarios which may be representative of the trend over time of some significant parameters for gas turbines. Moreover, the Baesyan Forecasting Method, which allows the detection of discontinuities in time series, is also tested for predicting system behavior after two consecutive trends. The results presented in this paper aim to select the most suitable methodology that allows both trending and forecasting as a function of data trend over time, in order to predict time evolution of gas turbine characteristic parameters and to provide an estimate of the occurrence of a failure.

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