W. Tabakoff

Erosion study of different materials affected by coal ash particles

Abstract Alloys in contact with coal particles or coal ash are exposed to erosion. The problem of predicting erosion is very complex. The present paper describes he test facility which is designed in such a way that the aerodynamic effects are an integral part of the erosion test parameters. Some results from the alloys studied (aluminum, stainless steel and titanium) in this investigation are reported.

Turbine Blade Surface Deterioration by Erosion

This paper presents the results of a combined experimental and computational research program to investigate turbine vane and blade material surface deterioration caused by solid particle impacts. Tests are conducted in the erosion wind tunnel for coated and uncoated blade materials at various impact conditions. Surface roughness measurements obtained prior and subsequent to the erosion tests are used to characterize the change in roughness caused by erosion. Numerical simulations for the three-dimensional flow field and particle trajectories through a low-pressure gas turbine are employed to determine the particle impact conditions with stator vanes and rotor blades using experimentally based particle restitution models. Experimental results are presented for the measured blade material/coating erosion and surface roughness. The measurements indicate that both erosion and surface roughness increase with impact angle and particle size. Computational results are presented for the particle trajectories through the first stage of a low-pressure turbine of a high bypass turbofan engine. The trajectories indicate that the particles impact the vane pressure surface and the aft part of the suction surface. The impacts reduce the particle momentum through the stator but increase it through the rotor. Vane and blade surface erosion patterns are predicted based on the computed trajectories and the experimentally measured blade coating erosion characteristics.

Investigation of coatings at high temperature for use in turbomachinery

Abstract Aircraft gas turbines, steam turbines and coal utilization turbines operating under particulate flows are exposed to erosion and performance deterioration. Almost all advanced aircraft turbines today are manufactured with a protective coating on the blades. The particulates in the steam turbines are produced in the boiler from exfoliated oxide scales and carried in the steam to the turbine. In coal utilization turbines, the particulates are by-products of the combustion process. There are many problem areas which need future research to be able to produce better and more durable high-temperature coatings. However, this paper will present only some of the work done at the University of Cincinnati on erosion testing at high temperatures and velocities for different materials and coatings. The testings have been performed with a special high-temperature erosion wind tunnel which simulates the aerodynamic conditions on the blades.

Some effects of temperature on the erosion of metals

Abstract The effect of temperature on the erosion of several metals was experimentally investigated. Theoretical considerations based on the temperature dependence of basic metallurgical processes were applied to analyze the results obtained. In general it was found that erosion damage may increase or decrease as the temperature increases, depending upon the angle at which the particles strike the material surface and upon the test temperature with respect to the thermal properties of the material.

Protection of coated superalloys from erosion in turbomachinery and other systems exposed to particulate flows

Abstract The design and development of high performance turbomachinery operating in an ambient with solid particles require a thorough knowledge of the fundamental phenomenon associated with particulate flows. This paper describes the overview of jet engines performance deterioration and retention. The ingestion of solid particles over period of time, will reduce the efficiency of the propulsion system, causing increased fuel consumption and thrust decrease. High pressure compressor and turbine design improvements are now developing and verifying experimentally different new ceramic coatings on superalloys such as INCO 718, Waspaloy and on SS410, subjected to gas particulate flows at high temperatures. The investigated coatings are produced by plasma spray, detonation guns, chemical vapor deposition (CVD), physical vapor deposition (PVD), and other methods. Experimental studies were conducted at the University of Cincinnati high temperature erosion wind tunnel to investigate the erosion behavior of coatings exposed to different types of solid particles. Some of the following coatings were evaluated: rhodium platinum aluminized, SDG-2207 (super D-gun product), CVD coatings, including TiC, TiN, Al2O3, and PVD coatings. The erosive wear of the samples was studied experimentally by exposing them to particle laden flow at velocities from 180 to 305 m s−1, temperatures from ambient to 815°C and impingement angles from 15° to 90°.

Numerical Simulation of a Dilute Particulate Flow (Laminar) Over Tube Banks

This paper presents an investigation of numerical simulation for a dilute particle laden flow (laminar) over in-line tube banks. Particles behavior of two different sizes and density (100 μm sand and 40 μm fly ash) is demonstrated through the present study for a fixed geometry and flow condition, that is, a square in-line tube bank of two rows deep with pitch-to-diameter ratio of two at Reynolds number 400. Dilute particulate flow assumption is used and the drag force is considered as the only external force term that affects the particles behavior in the flow. Experimental rebounding data and semiempirical equation for the erosion estimation are used. It was found through the present simulation that the particles behavior of the different sizes and density in tube bank system is quite different in their trajectories, impact and the erosion pattern. The protective role of the first row of cylinders could be supported with respect to the particles collision on the cylinder but not necessarily to the erosion point of view. Also the information at impact such as the impact velocity and the impact angle which affect the erosion (Tabakoff et al., 1988) can be estimated by using the numerical simulation shown in the present study.

High-temperature erosion resistance of coatings for use in turbomachinery

Industrial gas turbines, aircraft gas turbines, steam turbines and coal-utilization turbines, when operating under particulate flows, are exposed to erosion and performance deterioration. This paper describes an experimental method used to find the erosion behavior of superalloys and coatings subjected to gas-particle flows at high temperatures. The erosion behaviors are investigated experimentally at high temperatures using a specially designed erosion wind tunnel. The erosion results show the effects of velocity, temperature and impact angle on the erosion rate.

Laser Measurements of Fly Ash Rebound Parameters for Use in Trajectory Calculations

This paper describes an experimental method used to find particle restitution coefficients. The equations that govern the motion of solid particles suspended by a compressible gas flow through a turbomachine depend on the restitution coefficients. Analysis of the data obtained by a laser-Doppler velocimeter (LDV) system of the collision phenomenon gives the restitution ratios as a function of the incidence angle. From these ratios, the particle velocity components after collision are computed and used as the initial conditions to the solution of the governing equations of motion for particle trajectories. The erosion of metals impacted by small dust particles can be calculated by knowing the restitution coefficients. The alloy used in this investigation was 410 stainless steel.

Erosion rate testing at high temperature for turbomachinery use

Abstract A high temperature erosion test facility was designed by Tabakoff and Wakeman (Test facility for material erosion at high temperature, ASTM Special Publication , 664 (1979) 123–135) to provide erosion data in the range of operating temperatures experienced in compressors and turbines. In addition to the high temperatures, the facility properly simulates all the erosion parameters which were determined to be important from the aerodynamics point of view. These parameters include particle velocity, angle of impact, particle size, particle concentration and sample size. For a better understanding of the use of this tunnel and to obtain good results, definitions of the parameters used in the wind tunnel testings and test procedures are presented: for example, an experimental study which was conducted to investigate the erosion behavior of titanium carbide coating exposed to fly ash and chromite particles. The chemical vapor deposition technique (CVD) was used to apply a ceramic coating on nickel and cobalt based superalloys (M246 and X40). The test specimens were exposed to particle laden flow at velocities of 305 and 366 m s −1 and temperatures of 550°C and 815°C.

CVD diamond coating for erosion protection at elevated temperatures

Small solid particles entrained in a gas-fluid turbomachinery flow can cause degradation of the component surfaces containing the flow by erosion and corrosion processes. As diamond is the hardest known material, much work has been done to use polycrystalline diamond (PCD) as a protective coating on parts operating in a hostile and abrasive environment. Little attention is given in the literature to the high-temperature erosion behavior of chemical vapor deposition (CVD) diamond on different substrates. The objectives of this research were to develop CVD diamond erosion barriers for surface protection of cemented tungsten carbide at high temperatures and to study the erosion behavior of the coatings. Microwave plasma chemical vapor deposition (MPCVD) was used to apply diamond films on WC-6%Co. The erosion behavior of the coated specimens was investigated experimentally by exposing them to abrasive particle-laden flow in a high-temperature wind tunnel. The obtained results show the effects of impingement angle, temperature, and particle dose on the erosion rate. The data demonstrate that uncoated substrates suffer 6–7 times higher wear compared to diamond-coated samples at elevated temperatures up to 538 °C when exposed to alumina particle flow. This study indicates that polycrystalline diamond is emerging as a promising erosion protective coating for high-temperature applications.