Shroud Ring Research Articles

Effect of Ceramic Matrix Composites on the Thermal Efficiency of a Power Generation Turbine

Abstract Ceramic matrix composites (CMCs) offer higher allowable temperatures and reduced weight, making them an attractive prospect for parts in the hot section of a gas turbine engine. As CMCs are increasingly adapted into aero and land-based engines, there is a need to quantify the performance increase based on the potential for reduced cooling and increased firing temperatures. In this work, two static hot section components—the first-stage turbine vane and the first-stage turbine tip shroud (outer casing above the blade)—of a mid-sized power generation engine were modeled. Informed approximations about part geometry and cooling architectures were made to determine the cooling requirements of each part. Thermal boundary conditions for the turbine tip shroud and turbine vane were generated as a function of coolant mass flowrate using data from literature and applied to a 2D finite element analysis of the parts to determine maximum temperatures for both metallic and ceramic materials. A gas turbine cycle model was developed to simulate the performance of a mid-sized power generation turbine and used to determine the increase in efficiency due to a reduction in the cooling requirement for the CMC part compared to a conventional metal superalloy-based part. The potential reduction in chargeable cooling seen for the tip shroud ring was between 0.09% and 0.4% of the compressor mass flowrate, which corresponds to an increase in thermal efficiency between 0.11% and 0.45%. A similar analysis of the turbine vane resulted in a cooling reduction of 10.71% at the maximum turbine entry temperature considered which corresponds to a 3.4% increase in thermal efficiency.

AN IN-DEPTH INVESTIGATION ON KERF ANGLE IN PIERCED HOLE ON INCONEL-625 SUPERALLOY USING ABRASIVE WATERJET CUTTING PROCESS

This work investigates the piercing of microholes in turbine shroud rings (Inconel-625) using the Abrasive Waterjet Cutting process. The concern with the hole piercing is the kerf angle caused by the attenuation of the jet energy and stand-off distance, which seriously impacts the processing precision of abrasive water jet piercing. The effects of piercing parameters like machining time (40, 60 and 80[Formula: see text]s), abrasive mesh size (80 mesh and 120 mesh), stand-off distance (1, 2, 3 and 4[Formula: see text]mm), abrasive jet pressure (100, 125, 150 and 175[Formula: see text]MPa) are studied to reduce the kerf angle. The kerf angle increased linearly with a stand-off distance increase at different machining times. By piercing for 60[Formula: see text]s and 80[Formula: see text]s, the lowest values of kerf angle are obtained (0.03∘ and 0.02∘). The optimum conditions for making a pierced hole with a minimum kerf angle of 0.02∘ were achieved with a machining time- of 60[Formula: see text]s, abrasive mesh size- of 20 mesh, and abrasive jet pressure- of Scanning electron microscope (SEM) images and visual measuring system (VMS) images are used to identify the surface characteristics in kerf zone. The features, including ploughing, particle embedment, lip impression and wear path due to the ductile mode of erosion caused by high energy impact, is also discussed.

Исследование вибрационных и механических свойств обандаженных направляющих лопаток с предварительным натяжением

The article considers the effect of the stator blade tension of an axial compressor on blade vibration and mechanical properties. Attention is paid to modeling the stress-strain state of a pre-tensioned blade and calculating the strength of the developed model as well as modal analysis. A method of stator blade pre-tensioning is proposed: the blade root is fixed in the groove of the body, and fitting into the shroud ring is made with a gap providing the blades with the necessary space for stretching. The tension is adjusted by changing the position of the tightening nut. Nuts are tightened evenly around the circumference. The proposed method allows increasing the rigidity of the stator blades and, consequently, reducing their thickness in order to improve aerodynamic performance while maintaining vibration-frequency characteristics. The pre-tension has the greatest influence on bending shapes. The ability to regulate the natural vibration frequencies of the stator blade in a wide range allows avoiding resonance.

Identification and Estimation of Damage Severity in a Turbine Blade Packet Using Inverse Eigen-Value Analysis—A Numerical Study

Abstract Turbine blades are critical machine components in power plants and aerospace turbo engines. Failure of these blades in operation leads to catastrophic damages as well as high cost of maintenance and repair. Blades are often assembled in packets with lacing wire or shroud ring interconnections. Natural frequencies of the bladed packets are designed in a specific range to avoid possible resonant stresses. However, frequent damages during operation alter the stiffness of the blade-packet assembly and change the eigen-spectrum. A numerical study is presented in this work, where it is demonstrated that characteristic changes in eigen-spectrum can identify both severity and location of such damages. The work employs matrix perturbation theory on the eigen-value problem, formulated from the lumped-parameter modeling of the blade packet. Damage is considered as a perturbation in the stiffness matrix with damage severity acting as the perturbation parameter. First, a graphical pattern recognition method, and then, a damage proximity index evaluation method is suggested for damage identification. Further, an estimation algorithm for damage severity is presented with numerically simulated computations, which demonstrates that the methods can exactly identify the damage location and, with very little error, can estimate the damage severity.

A nets fixing device embedded in a circular floating net cage

A nets fixing device embedded in a circular floating net cage is presented in this paper, it consists of arc metal rods, wire ropes and sleeves. The arc metal rod is a circular arc metal rod with a connecting plate at both ends and a shroud ring at the inner side of the middle. Multiple arc metal rods can be fixedly connected to form a ring shape; During assembly, each arc metal rod is assembled into a circular ring. A wire rope is bound on each ring of a circular arc metal rod, and then the wire rope is pulled to sink the circular arc metal rod into the water inside the cage. Then, in the depth range of the nets, the interval and alternating sleeves of the wire ropes are inserted into the casing pipe and the circular arc metal bars, and the wire ropes are straightened and bound to the cage frame, thus forming the nets fixing device. The proposed device has simple structure, light weight, less material, high strength, and low overall price, which can effectively reduce the volume loss rate of nets, and is convenient for installation and removal.

An Experimental Study of the Leakage Flow Effect on the Film Cooling Effectiveness of a Gas Turbine Shroud

Abstract In the vicinity of gas turbine blades, a complex flow field is formed due to the flow separation, reattachment, and secondary flows, and this results in a locally non-uniform and high heat transfer on the surfaces. The present study experimentally investigates the effects of leakage flow through the slot between the gas turbine vane and blade rows on the film cooling effectiveness of the forward region of the shroud ring segment. The experiment is carried out in a linear cascade with five blades. Instead of the vane, a row of rods at the location of the vane trailing edge is installed to consider the wake effect. The leakage flow is introduced through the slot between the vane and blade rows, and additional coolant air is injected from the cooling holes installed at the vane’s outer zone. The effects of the slot geometry, cooling hole configuration, and blowing ratio on the film cooling effectiveness are experimentally investigated using the pressure-sensitive paint (PSP) technique. CO2 gas and a mixture of SF6 and N2 (25% + 75%) are used to simulate the leakage flow to the mainstream density ratios of 1.5 and 2.0, respectively. The results indicate that the area-averaged film cooling effectiveness is affected more by the slot width than by the cooling hole configuration at the same injection conditions, and the lower density ratio cases show higher film cooling effectiveness than the higher density ratio case at the same cooling configuration.

Optimizing bidirectional impulse turbines for thermoacoustic engines.

The design of a bidirectional impulse turbine to convert thermoacoustic power into electricity is experimentally optimized. The turbine efficiency is measured for rotors with and without a shroud ring and for a varying tip clearance. Furthermore, the axial spacing between the guide vanes and rotor is varied with respect to the displacement amplitude of the acoustic wave. All measurements are carried out for several turbine loads and acoustic frequencies. For a chosen implementation, a design study on the guide vane and rotor blade geometry is presented to further optimize the bidirectional impulse turbine for thermoacoustic engines.

Interrelated Dimensional Chains in Predicting Accuracy of Turbine Wheel Assembly Parameters

The working capacity of any device primarily depends on the assembly accuracy which, in its turn, is determined by the quality of each part manufactured, i.e., the degree of conformity between final geometrical parameters and the set ones. However, the assembly accuracy depends not only on a qualitative manufacturing process but also on the assembly process correctness. In this connection, there were preliminary calculations of assembly stages in terms of conformity to real geometrical parameters with their permissible values. This task is performed by means of the calculation of dimensional chains. The calculation of interrelated dimensional chains in the aircraft industry requires particular attention. The article considers the issues of dimensional chain calculation modelling by the example of the turbine wheel assembly process. The authors described the solution algorithm in terms of mathematical statistics implemented in Matlab. The paper demonstrated the results of a dimensional chain calculation for a turbine wheel in relation to the draw of turbine blades to the shroud ring diameter. Besides, the article provides the information on the influence of a geometrical parameter tolerance for the dimensional chain link elements on a closing one.

Numerical investigation of suction vortices behavior in centrifugal pump

A numerical simulation on suction vortices behavior in a centrifugal pump was carried out to investigate their influence on the internal flow through impellers including formation and shedding of cavitation by using a finite-volume method and k-ω Shear Stress Transport turbulence model. For cavitating flow, a two phase homogeneous cavitation model was used. A full three-dimensional flow in a single-section centrifugal pump consisting of a six blade impeller and shroud ring was computed with structured mesh. A constant suction vortex is imposed as a boundary condition. Vortices behavior was investigated according to the variation of flow rates of two pump systems with and without suction vortices. From the results, suction vortices induced biased flow structure and more cavitations, especially at the low flow rate condition. Complicated internal flow phenomena through impellers such as formation of cavitations, growing and shedding of the vortex, flow separation and flow unsteadiness due to the suction vortices are investigated and discussed.

양흡입 원심펌프에 있어서 유량변화의 영향에 관한 수치해석적 연구

A numerical simulation is carried out to investigate the effect of flow rate variation and performance characteristics of double-suction centrifugal pump. Two types of pump which have different impeller inlet breadth and curvature of the shroud line consist of six blades impeller and shroud ring. Finite-volume method with structured mesh and k-ω Shear Stress Transport turbulence model was used to guaranty more accurate prediction of turbulent flow in the pump impeller. Total head, power and overall efficiency were calculated to obtain performance characteristics of two types of pump according to the variation of flow rate. From the results, impeller having smooth curve along the shroud line obtained good performance. The lower flow rate, the more circulation region, flow unsteadiness and complicate flow pattern are observed. Complicated internal flow phenomena through impellers such as flow separation, pressure loss, flow unsteadiness and performance are investigated and discussed.

Experience with technical diagnostics of generator shroud rings at thermal plants

Experience with the application of the method of magnetic memory of metal while controlling the state of the generator shroud rings for in-time recognition of damage that develops in the zones of stress concentration is considered.

Thermoelastic Contact of a Shroud Ring and a Cylinder under Unsteady Friction-Induced Heat Release

Mathematical formulation is performed and a solution is found for a quasi-static thermoelastic problem of contact interaction of an elastic shroud ring and a hollow circular cylinder inserted into this ring, which are compressed by a load varied along the axis of the system, under the condition of an unloaded contact over the ring surface or over the circumference contour. The radial displacements of the contact surface of the shroud ring are approximated by displacements of the surface of a long circular hollow cylinder. Unsteady friction-induced heat release caused by the action of friction forces owing to shroud ring rotation over the cylinder with a time-dependent low angular velocity is taken into account. The problem is reduced to a system of integral equations whose structure is determined by the form of thermophysical contact conditions. A numerical algorithm of the solution is proposed, and the influence of the problem parameters on the contact pressure and temperature distributions is considered. Based on an analysis of results, a conclusion is made that the character of axial variation of the compressing load has a significant effect on the distribution of contact pressure in describing the kinematic condition of interaction of bodies in accordance with Hertz’s theory.

Rig and Engine Testing of Melt Infiltrated Ceramic Composites for Combustor and Shroud Applications

General Electric has developed SiC fiber-reinforced SiC-Si matrix composites produced by silicon melt infiltration for use in gas turbine engine applications. High temperature, high-pressure combustion rig testing, and engine testing has been performed on combustor liners and turbine shrouds made from such MI composites. Frame 5 sized combustor liners were rig tested under lean head end diffusion flame conditions for 150 hours, including 20 thermal trip cycles, with no observed damage to the ceramic liners. Similarly, 46-cm diameter, single-piece turbine shroud rings were fabricated and tested in a GE-2 gas turbine engine. The fabrication and testing of both components are described.

Corrosion-mechanical characteristics of the materials of nonmagnetic shroud rings of turbogenerators. I. 8Mn−8Ni−4Cr and 18Mn−4Cr steels

On the basis of the comprehensive analysis of the corrosion-mechanical characteristics of austenitic nonmagnetic 8Mn−8Ni−4Cr steels, we show that this type of steel is susceptible to corrosion cracking even in low-aggressive aqueous solutions, including humid working environments at a temperature of 80°C. The application of aluminum coatings and mechanical surface treatment increase the time to failure of specimens. Only deep drying of hydrogen used to cool the shrouds eliminates the causes of corrosion cracking of these types of steel. The procedure of cold tensile hardening cannot be applied to 40Kh4G18 steel because it is characterized by high susceptibility to the formation of α-martensite in the process of plastic deformation due to the insufficient stability of austenite. The optimal vanadium contents of steel guaranteeing its high strength and plastic characteristics lie within the range 1.3–1.5%. In the absence of water, 18Mn−4Cr steel does not exhibit any noticeable susceptibility to corrosion cracking. For this reason, the main condition that should be realized to prevent corrosion cracking and corrosion fatigue of shroud rings is the maintenance of the dry state of working environments in the processes of manufacturing, storage, and transportation of these rings, in service, and during downtimes. The presence of Cl− ions, hydrogen sulfide, halides, and nitrates in the working environments significantly enhances the fatigue crack growth rates in the entire investigated range. These ions also promote crack growth under the conditions of long-term static loading.

Application of ribbed-plate surfaces for intensifying heat exchange in oil coolers

We investigated the heat transfer upon motion of oil in ribbed-plate heat exchangers with perforated and discontinuous shruds and tubular heat exchangers with annular channels filled with a discontinuous shroud and perforated rings

A NOTE ON NATURAL VIBRATIONS OF TURBINE BLADE ASSEMBLIES WITH NON-CONTINUOUS SHROUD RINGS

Natural frequencies and natural mode shapes for models of turbine blade assemblies with non-continuous shroud rings are calculated numerically and investigated experimentally. A good agreement between the results of analysis and testing is observed for a theoretical model with additional degrees of freedom at shroud ring interfaces.

舶用過給機のタービン部における浸食損傷の発生状況に関する調査報告

During the latest four years, the abrasive erosion was frequently found on Stator Blades, Rotor Blades and Rotor Blade Shroud Ring of the turbo-charger of the main propulsion diesel engine and the dynamo engine.This kind of the damage was rarely found before some yaers ago and the usual damages were the corrosion on the gas casing, the cracks at the root of the stator blades and the hit by the broken pieces of piston ring, exhaust valve and others.This research was carried out on 102 ships during September, 1987 and August, 1988.The result of this research showed posibility that cause of the erosion was mainly low grade high viscosity heavy fuel oil including some hard fine particles.

Assimilation and improvement of production technology for nonmagnetic shroud rings for turbogenerators

Assimilation and improvement of production technology for nonmagnetic shroud rings for turbogenerators

A vibration analysis of a turbine blade system damped by dry friction forces

A turbine blade system with dry friction between the shroud ring elements is analysed and results obtained by a finite element method, are presented. Friction forces in the interacting surfaces are described in terms of anisotropic dry friction theory. In the examples, frequencies and mode shapes of undamped free vibrations of the system are analysed. Vibration excitation due to friction and vibration coupling caused by friction anisotropy are described when vibration is initiated by prescribed displacements or velocities.

Lift and Drag Measurements on a Hydrofoil in Dilute Polyox Solutions

THE use of hydrofoils for a wide variety of purposes such as propeller blades on boats, as sailboat keels, ship rudders, submarine and torpedo fins, lifting surfaces of hydrofoil boats, and shroud ring stabilizers for missiles, has prompted efforts to increase the lift-to-drag ratio by various means. The favourable drag reducing effect of polymers, particularly for flows in pipes1, suggests that they might be of value in increasing this ratio.