A discussion on deformation of solids by the impact of liquids, and its relation to rain damage in aircraft and missiles, to blade erosion in steam turbines, and to cavitation erosion - Observation of events leading to the formation of water drops which cause turbine blade erosion

1966 ◽  
Vol 260 (1110) ◽  
pp. 183-192 ◽  
Keyword(s):  
Turbine Blade ◽  
High Speed ◽  
Maximum Velocity ◽  
Low Pressure ◽  
Background Information ◽  
Maximum Diameter ◽  
Steam Turbines ◽  
Subsequent Formation ◽  
Water Drops ◽  
The Impact

The large blades required in the last low pressure stages of modern turbines of 350 MW and above makes them more susceptible to erosion by wet steam owing to the increase in blade tip velocity. A specially developed periscope combined with a cine camera has been used for viewing inside an operating turbine to record the flow of water over the fixed blades and the subsequent formation and stripping of the water drops which then impact on the moving blades causing erosion. The drops had a maximum diameter of 450 /mi and the estimated total mass of the drops impacting on the blades was only a few per cent of the mass flow of water condensed from the steam. This confirms that the condensed steam forms a fog of droplets which are so small that only a very small proportion of them is captured by the turbine surfaces to produce large drops capable of causing erosion. In addition to the direct practical value of these observations, the data provide background information in support of the high speed photographic studies of the drop-forming processes on a blade cascade in the laboratory. Experiments in a steam tunnel in which the turbine low pressure steam conditions can be simulated, indicate that drops of 350 to 1600 /xm leave the trailing edge of a blade and accelerate to a maximum velocity of 70 ft./s over a distance of about 1 in. in the blade wake. They are then caught in the main steam flow, which has a velocity of up to 1200 ft./s, where they are broken up and rapidly accelerated. Analysis of the cine films of observations in a turbine and in the steam tunnel gives the velocities and sizes of the drops causing turbine blade erosion.

A discussion on deformation of solids by the impact of liquids, and its relation to rain damage in aircraft and missiles, to blade erosion in steam turbines, and to cavitation erosion - Disintegration of raindrops by shockwaves ahead of conical bodies

1966 ◽  
Vol 260 (1110) ◽  
pp. 153-160 ◽  
Keyword(s):  
High Speed ◽  
Empirical Relation ◽  
Aircraft Design ◽  
The Body ◽  
Drop Diameter ◽  
Steam Turbines ◽  
Supersonic Flight ◽  
Water Drops ◽  
Time Required ◽  
The Impact

When an aircraft flies at high speed through rain the impact of raindrops on the forward facing surfaces of the aircraft may cause severe erosion damage depending on the size and number of the drops, the speed of the aircraft and the time of flight in the rain. However, before the raindrops reach the aircraft surface they have to pass through a region where they are subjected to relative air velocities caused by the airflow round the aircraft surface. This is particularly applicable to supersonic flight when, in the region between the shockwaves and the aircraft surface, the raindrops may be exposed to air velocities large enough to disintegrate them. The raindrop disintegration is not an instantaneous event; it takes short but finite time and appears to be an erosion process whereby droplets are torn off the surface of the main drop until it is completely reduced to a fine mist. The degree of disintegration of a drop by the time it reaches the aircraft surface will depend on the magnitude of, and the exposure time to, the air velocity. For supersonic flight this time depends on the distance travelled by the drop between the shockwave and the aircraft surface. The experiments described had the object of determining the time required for high speed airstreams completely to disintegrate water drops. An empirical relation is postulated between D , the drop diameter, V , the airstream velocity and t , the time for complete disintegration. The paper considers a conical body at supersonic velocity in a raindrop environment, the body being of a shape typical of that envisaged for supersonic aircraft design. From the derived empirical relation for the time of disintegration of water drops the size of drops to be completely disintegrated when approaching the surface of cones of different vertex angles has been calculated for a range of flight Mach numbers. An experiment giving partial justification for computed results is described.

Numerical Investigation of Contrasting Flow Physics in Different Zones of a High-Lift Low-Pressure Turbine Blade

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Jiahuan Cui ◽  
V. Nagabhushana Rao ◽  
Paul Tucker
Keyword(s):  
Boundary Layer ◽  
Turbine Blade ◽  
Low Pressure ◽  
The State ◽  
Suction Surface ◽  
Flow Physics ◽  
Pressure Surface ◽  
Low Pressure Turbine ◽  
Flow Features ◽  
The Impact

Using a range of high-fidelity large eddy simulations (LES), the contrasting flow physics on the suction surface, pressure surface, and endwalls of a low-pressure turbine (LPT) blade (T106A) was studied. The current paper attempts to provide an improved understanding of the flow physics over these three zones under the influence of different inflow boundary conditions. These include: (a) the effect of wakes at low and high turbulence intensity on the flow at midspan and (b) the impact of the state of the incoming boundary layer on endwall flow features. On the suction surface, the pressure fluctuations on the aft portion significantly reduced at high freestream turbulence (FST). The instantaneous flow features revealed that this reduction at high FST (HF) is due to the dominance of “streak-based” transition over the “Kelvin–Helmholtz” (KH) based transition. Also, the transition mechanisms observed over the turbine blade were largely similar to those on a flat plate subjected to pressure gradients. On pressure surface, elongated vortices were observed at low FST (LF). The possibility of the coexistence of both the Görtler instability and the severe straining of the wakes in the formation of these elongated vortices was suggested. While this was true for the cases under low turbulence levels, the elongated vortices vanished at higher levels of background turbulence. At endwalls, the effect of the state of the incoming boundary layer on flow features has been demonstrated. The loss cores corresponding to the passage vortex and trailing shed vortex were moved farther from the endwall with a turbulent boundary layer (TBL) when compared to an incoming laminar boundary layer (LBL). Multiple horse-shoe vortices, which constantly moved toward the leading edge due to a low-frequency unstable mechanism, were captured.

Observation of splash generated immediately after the impact of a high-speed droplet in a low-pressure

2018 ◽  
Vol 2018 (0) ◽  
pp. OS2-9
Author(s):  
Taku ASHIDA ◽  
Masao WATANABE ◽  
Kazumichi KOBAYASHI ◽  
Hiroyuki FUJII ◽  
Toshiyuki SANADA
Keyword(s):  
High Speed ◽  
Low Pressure ◽  
The Impact

A Methodology for a Detailed Loss Prediction in Low Pressure Steam Turbines

2017 ◽  
Author(s):  
Marius Grübel ◽  
Robin M. Dovik ◽  
Markus Schatz ◽  
Damian M. Vogt
Keyword(s):  
Boundary Layer ◽  
Evaluation Method ◽  
Three Dimensional ◽  
Low Pressure ◽  
Steam Turbines ◽  
Cfd Simulations ◽  
Depth Analysis ◽  
Pressure Steam ◽  
The Impact ◽  
Loss Mechanisms

An evaluation method for CFD simulations is presented, which allows an in-depth analysis of different loss mechanisms applying the approach of entropy creation proposed by Denton. The entropy creation within each single mesh element is determined based on the entropy flux through the cell faces and therefore the locations, where losses occur, can be identified clearly. By using unique features of the different loss mechanisms present in low pressure steam turbines, the losses are categorized into boundary layer, wake mixing and shock losses as well as thermodynamic wetness losses. The suitability of the evaluation method is demonstrated by means of steady state CFD simulations of the flow through a generic last stage of a low pressure steam turbine. The simulations have been performed on streamtubes extracted from three-dimensional simulations representing the flow at 10 % span. The impact of non-equilibrium steam effects on the overall loss composition of the stator passage is investigated by comparing the results to an equilibrium steam simulation. It is shown, that the boundary layer losses for the investigated case are of similar magnitude, but the shock and wake losses exhibit significant differences.

A discussion on deformation of solids by the impact of liquids, and its relation to rain damage in aircraft and missiles, to blade erosion in steam turbines, and to cavitation erosion - Conclusion

1966 ◽  
Vol 260 (1110) ◽  
pp. 311-315
Keyword(s):  
High Speed ◽  
Rear Surface ◽  
Peak Load ◽  
Brittle Materials ◽  
Front Surface ◽  
Drop Impact ◽  
Surface Flow ◽  
Steam Turbines ◽  
Brittle Solids ◽  
The Impact

Basic studies show that the measured impact pressure can be accounted for by assuming compressible deformation of the liquid drop in the first stages of impact. The distribution of pressure under a drop produces a shallow indentation in the surface of ductile solids and a ring fracture in brittle materials. The flow of liquid across the surface from under the drop leads to erosive shearing along the edges of the deformed area. Although in theory erosion due to surface flow would not occur on perfectly smooth surfaces, ideal conditions of this kind are impracticable. The smallest discontinuities (step heights down to about 1000 A) have been shown to act as nuclei for erosion pits. The short duration of the peak load during drop impact gives the impact an explosive character. In brittle materials the reflexion and interference of stress waves can cause extensive fracture in regions remote from the initial impact area. Spalling of the rear surface of a thin plate due to drop impact on the front surface could be an important mechanism in the failure of ceramic radomes in high speed aircraft and missiles. To some extent the strength of brittle solids can be improved by treatments which alter the size or number of surface flaws.

A discussion on deformation of solids by the impact of liquids, and its relation to rain damage in aircraft and missiles, to blade erosion in steam turbines, and to cavitation erosion - The resistance of materials to impact erosion damage

1966 ◽  
Vol 260 (1110) ◽  
pp. 193-203 ◽  
Keyword(s):  
Mechanical Properties ◽  
Mass Loss ◽  
Incubation Period ◽  
Turbine Blade ◽  
Cavitation Erosion ◽  
Steam Turbines ◽  
Microstructural Characteristics ◽  
Erosion Damage ◽  
The Impact ◽  
Impact Erosion

The behaviour of established and potential turbine blade and erosion shield materials subject to impact erosion by water droplets of controlled size has been investigated over a range of impact velocities up to 1040 ft./s. Both the topographical form and the microstructural characteristics of damage have been studied, and correlated with the conditions of the test and the mechanical properties and phase constitution of the materials. It has been found that the rate of erosion, as measured by mass loss, changes during the course of a test. An initial incubation period is generally followed, successively, by periods of increasing, constant, and then decreasing rates of erosion, possibly culminating in a second steady, but lower, rate of erosion.

Scaling 3D Low-Pressure Turbine Blades for Low-Speed Testing

2015 ◽  
Author(s):  
Matteo Giovannini ◽  
Michele Marconcini ◽  
Filippo Rubechini ◽  
Andrea Arnone ◽  
Francesco Bertini
Keyword(s):  
Turbine Blade ◽  
High Speed ◽  
Large Scale ◽  
Mechanical Design ◽  
General Procedure ◽  
Turbine Blades ◽  
Low Pressure ◽  
Low Speed ◽  
Open Rotor ◽  
Inlet Conditions

The present activity was carried out in the framework of the Clean Sky European research project ITURB (“Optimal High-Lift Turbine Blade Aero-Mechanical Design”), aimed at designing and validating a turbine blade for a geared open rotor engine. A cold-flow, large-scale, low-speed (LS) rig was built in order to investigate and validate new design criteria, providing reliable and detailed results while containing costs. This paper presents the design of a LS stage, and describes a general procedure that allows to scale 3D blades for low-speed testing. The design of the stator row was aimed at matching the test-rig inlet conditions and at providing the proper inlet flow field to the blade row. The rotor row was redesigned in order to match the performance of the high-speed one, compensating for both the compressibility effects and different turbine flow paths. The proposed scaling procedure is based on the matching of the 3D blade loading distribution between the real engine environment and the LS facility one, which leads to a comparable behavior of the boundary layer and hence to comparable profile losses. To this end, the datum blade is parameterized, and a neural-network-based methodology is exploited to guide an optimization process based on 3D RANS computations. The LS stage performance were investigated over a range of Reynolds numbers characteristic of modern low-pressure turbines by using a multi-equation, transition-sensitive, turbulence model.

scholarly journals Design Space Exploration of Turbine Blade Shroud Interlock for Flutter Stability

2020 ◽  
Author(s):  
Olatz Larrieta ◽  
Roberto Alonso ◽  
Óscar Pérez Escobar ◽  
Ibrahim Eryilmaz ◽  
Vassilios Pachidis
Keyword(s):  
Modal Analysis ◽  
Turbine Blade ◽  
High Speed ◽  
Design Space Exploration ◽  
Twist Angle ◽  
Low Pressure ◽  
Axial Position ◽  
Design Parameters ◽  
Low Pressure Turbine ◽  
Contact Position

Abstract The geared turbofan engines bring the potential to rotate the fan at lower speed and allow an increase in diameter, which in turn leads to an increase in propulsive efficiency through high by-pass ratio. The low-pressure turbine stages driving the fan can also rotate at high speed resulting in fewer stages when compared to traditional turbofans. However, when operating at high speed, pressure fluctuations due to self-excited vibrations increase and may provoke flutter instabilities. In a geared architecture, to deliver the high power required by the fan and the intermediate-pressure compressor, the low-pressure turbine system operates at higher temperatures compared to its predecessors. This phenomenon requires structural materials with higher heat resistance, which carries the inconvenience of poor welding suitability. That is the reason why alternative non-welded blade shroud joint techniques are so important, techniques as the blade interlock mechanism studied in this work. This manuscript examines the effects of different design parameters of a low-pressure turbine blade shroud interlock on flutter stability, to make future recommendations for geared engines. The shrouded turbine rotor blades feature blade interlocks, which enhances the dynamic stability by providing stiffness to the rotor blade row. To assess the stability of the system, a parametric design of a turbine blade-disk assembly was prepared. In the parametric model the design variables that define the blade interlock are the interlock angle, interlock axial position, interlock contact length and height, knife seal position and pre-twist angle. After parametrization, a finite element model of the turbine blade and disk assembly was prepared with cyclic symmetry boundary condition. The stresses caused by rotation were calculated in a static structural analysis and these were used as pre-stress boundary conditions in modal analysis. The modal results were afterwards exchanged with an aerodynamic model to obtain the aerodynamic damping for different blade interlock design configurations. In the present work, the dynamic response of the first three excitation modes was analyzed. It was found that the third mode was stable for all the design points, whereas first and second modes were unstable at least for the reference design point. Among the considered six different parameters that define the blade interlock geometry, the interlock contact position turned to be the most influential parameter for modal response and for flutter stability. Moving the interlock contact position towards the trailing edge gave the most beneficial results. On the other hand, the interlock angle showed the least influence on both, the modal analysis and flutter behavior. The accomplished Design of Experiments and subsequent optimization process also conclude that there exists an interdependency between the studied parameters.

A discussion on deformation of solids by the impact of liquids, and its relation to rain damage in aircraft and missiles, to blade erosion in steam turbines, and to cavitation erosion - Some aspects of rock cutting by high speed water jets

1966 ◽  
Vol 260 (1110) ◽  
pp. 295-310 ◽  
Keyword(s):  
Pressure Distribution ◽  
High Speed ◽  
Frictional Heating ◽  
Water Jet ◽  
Short Exposure ◽  
Maximum Pressure ◽  
Steam Turbines ◽  
Target Plate ◽  
Water Jets ◽  
The Impact

When rocks are cut in coal mines by steel picks, frictional heating sometimes causes ignition of methane; high speed water jets may provide a method of cutting which is free from this hazard. A high speed water jet emerging from a nozzle slows down with increasing distance from the nozzle and breaks up into water drops. Studies were made of the behaviour of water jets: in most of the experiments the jets were produced by pressures of 600 atm., but some results are given of experiments at pressures up to 5000 atm. The jets were examined by short exposure optical photography with several different methods of illumination (parallel transmitted, diffuse, and schlieren) and by X-ray photography. In order to find out how the jet velocity decays with distance from a nozzle, and to compare nozzle designs, a target plate containing a hole smaller than the jet diameter was placed so that the jet impinged at right angles on to it, and the target plate was moved until the maximum pressure at the hole was found: this was measured for different distances from the nozzle. Nozzle shapes suggested in literature for minimizing jet dispersion were studied and an empirical investigation of a variety of nozzle shapes was carried out. Several nozzle shapes were found which gave good results, i.e. the maximum pressure on the target plate was half the pump pressure at a distance of about 350 nozzle diameters. In many cutting applications the first stage in the process would be the impingement of a water jet on a surface at right angles. The initial cutting would depend upon the stress distribution within the target, which in turn would depend upon the pressure distribution produced by the water jet on the surface. A theory is given of the pressure distribution on the target plate, which predicts that the pressure will fall to zero at about 2.6 jet radii: this was found to be in good agreement with experiments. Preliminary studies were made of the penetration of several types of rock by water jets of velocities up to about 1000 m/s (pressures about 5000 atm). It was found that a 1 mm diameter jet drills a cylindrical hole about 5 mm in diameter. The pressure that the water jet produces at the bottom of such holes was measured and shown to fall off to about one-tenth of the nozzle pressure at a hole depth of about 4 cm.

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