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Hump characteristic is one of unique hydraulic instabilities of pump-turbines, which restricts the stable and safe operating range of the units. High-amplitude pressure fluctuations could be observed in the hump region, leading to hydraulic vibration of pumped storage power plants. To reduce the high-amplitude pressure fluctuation in the hump region, two optimization strategies for high-pressure edge shape of runner blades have been proposed. One is to increase the outlet angle near the shroud and the other increases the radius near the shroud. A large eddy simulation, which has been validated using performance and pressure fluctuation experiments, was performed to study the optimization effect. The valley point (0.65QBEP) in the hump region was selected for conducting time and frequency analyses under different optimization strategies. Analyses show that the pressure fluctuations were primarily caused by the rotation of three low-pressure regions at the circumference of the guide vanes. Both optimization strategies reduced the stall vortices formed in the three low-pressure regions and mitigated the rotating stall phenomenon. The influence of the runner-outlet geometries on pressure fluctuations is primarily reflected in the amplitude reduction of the dominant low frequency 0.2fn (where fn denotes the rotational speed) in the vaneless region and guide/stay vanes. Compared with strategies involving larger outlet angles near the shroud, this strategy of increasing the radius can more effectively reduce the amplitude of the dominant low frequency, and it makes the circumferential distribution of pressure fluctuations more uniform. These findings can help guide efforts in pump-turbine design optimization, which have been applied in a 700 m head pump-turbine design.

This study aims to present the comparison between 2 different nickel-based superalloy materials, rene 41 and waspaloy through their application in designing a high-pressure (HP) turbine blade for a turboshaft engine. NACA 4-digit airfoil profile has been used to create the airfoil for the HP turbine blade. MATLAB software is used to create a graphical user interface for the selection of various parameters used to define the airfoil profile including the NACA airfoil number, angle of attack, number of grid points, grid type, trailing edge type, chord length, and the plot style. For this study, NACA 9618 airfoil is used to model a single HP turbine blade. Numerical flow analysis using vortex panel method (VPM) is carried out on the airfoil to obtain the flow characteristics. Further, several types of failure methodologies occurring in the turbine blades and standard industrial methods used to reduce failure cycles are discussed. Comparisons are carried out showing precipitation-hardened rene 41 exhibiting relatively larger Von-Mises stress values in comparison with age-hardened waspaloy at elevated temperature for thermo-mechanical loading in the blade structure. Steady-state simulation at 39,000 rpm yields maximum temperature values of 1056 °C and 1220 °C for rene 41 and waspaloy respectively, also yielding relatively close values for critical displacement at the shroud section of the blade. Analysis models are proposed to determine the effect of mechanical and thermal loads on the high-pressure turbine blade design.

A tundish is a device from which liquid steel is pour into a mold. Therefore tundish hydrodynamic conditions have a significant impact on solidification during continuous steel casting (CSC) process. Modification of ladle shroud workspace, allows for the modification of liquid steel movement in the tundish. In the following work, numerical simulations were performed which allowed the impact of the modification of the ladle shroud workspace on the liquid steel flow structure in a one-strand tundish to be determined. In order to assess the impact of the modification of the ladle shroud on the behavior of the liquid steel in the tundish, simulations were performed, on the basis of which the percentage share of stagnant, ideal mixing and plug flow zones were determined. In addition, the mixing parameters were determined, allowing the estimation of casting duration during sequential casting. The flow fields of liquid steel for each modification of the ladle shroud were performed. The average velocity of liquid steel flowing through the tundish, the Reynolds number and turbulent intensity were also described. The obtained results showed, among others, that the application of three cylinders with a diameter of 0.041 m into the ladle shroud with a diameter of 0.11 m increases the share of active flow in the tundish in relation to the tundish with Conventional Ladle Shroud. At the same time, applying a ladle shroud with a diameter of 0.11 m during casting is the most favorable in relation to the hydrodynamics of the tundish.

This paper presents those flow parameters at which coherent structures appear in the blade tip cavities of shrouded turbine blades. To the authors’ knowledge, this is reported for the first time in the open literature. The unsteady flow in a shroud cavity is analysed based on experimental data recorded in a labyrinth seal test rig. The unsteady static wall pressure in the shroud cavity inlet and outlet is measured using time-resolving pressure sensors. Sensors are located at staggered circumferential positions to allow cross-correlation between signals. The unsteady pressure signals are reduced using Fourier analysis and cross-correlation in combination with digital filters. Based on the data, a theory is formulated explaining the phenomena reflected in the measurements. The results suggest that pressure fluctuations with distinct numbers of nodes are rotating in the shroud cavity outlet. Moreover, modes with different node numbers appear to be superimposed, rotating at a common speed in circumferential direction. The pressure fluctuations are not found at all operating points. Further analysis indicates that the pressure fluctuations are present at operating points matching distinct parameters correlating with the cavity flow coefficient. Unsteady RANS simulations predict similar flow structures for the design operating point of the test rig.

The fan installed in the outdoor unit of air-conditioning (AC) systems is often partially shrouded to increase the inlet area and allow the installation of a larger upstream heat exchanger. However, the effect of radial inflow from the unshrouded part on the aerodynamic performance of the fan is seldom studied. The current paper studies the flow structure in a partially shrouded fan to understand the effects of radial inlet flow on the main flow and the flow in the tip region. The results showed that the flow from the unshrouded region has the same scale as the axial inflow in a partially shrouded fan. The flow field and tip leakage vortex development in the partially shrouded fan are substantially different and the loss corresponding to the TLV is intensified compared to the fully shrouded one. In a partially shrouded fan, the TLV rolls up adjacent to the tip section due to the interaction with radial inflow and follows the tip chord in the unshrouded part. The TLV then moves away from the suction surface in the shrouded part inducing a large blockage and loss at the fan outlet. A vortex street is created outside the fan by the exiting TLV which restricts the main flow from radial expansion and increases the fan backpressure. The reverse flow near the shroud is mainly driven by the TLV and can be controlled by changing the TLV trajectory.

Exhaust Gas Temperatue is an parameter where the hot gases’s temperature leave the gas turbine. Exhaust gas temperature margin is the difference between highest temperature at take off phase with redline on indicator (???????????? ???????????????????????? °????=???????????? ????????????????????????????−???????????? ???????????????? ????????????). EGTM is one of any factor to determine engine performance. A good perfomance of an engine when it has a big margin (EGTM), during operation of an engine the EGTM could decrease untill 0 (zero). So many factors could affect EGTM deteroration there are: distress hardware such as airfoil erosion, leak of an airseals, and increase of clearance between tip balde and shroud. Increase of clearance happens in high pressure compressor rotor clearance. In CFM56-7 have 9 stage(s) of high pressure compressor and each stage give the EGT Loses. The calculation of EGT Effect/Losses is actual celarance – minimum clearance x 1000 x EGT Effect °C, where actual clearance define by the substraction of outside diameter’s rotor with inside diameter’s shroud, minimum clearance define in the manual, 1000 is adjustment from mils/microinch to inch, and EGT Effect is temperature that define in the manual. The analysist had done with 6 (six) engine serial number and proceed by corelation that shown linkage between clearance and EGT Effect, the corelation is strong shown the result of corelation (r) is 0.994275999 or nearest 1.

A novel ladle shroud was employed to produce small bubbles to remove inclusions smaller than 50 μm meanwhile inhibiting the formation of slag eye. Both water modeling and industrial tests were carried out to confirm the generation of small bubbles with the ladle shroud. The numerical model was developed to investigate slag-metal interfacial behaviors, considering the effects of bubble sizes and distributions. The gas flux through the surface was employed to evaluate the impact of bubble swarm on slag layer. The results show that reducing bubble sizes can effectively disperse bubbles passing through the slag layer, so as to inhibit the formation of slag eye, under the same gas flow rate. The diameter of slag eye matches well 1.7 times diameter of the region with gas flux higher than 0.0025 m/s. The heat loss of the entire tundish was estimated, considering the convection and radiation heat transfer of slag eye.

The purpose of the investigation is to obtain the mechanism of affecting the performance and stability of an axial flow compressor with two kinds of multi distortion area. In the investigation, the compressor inlet distortion is made by the distortion generator, which is a column and is placed in the compressor rotor passage upstream. The five-passages unsteady numerical results show that the compressor performances for two kinds of multi distortion area are both lower than that for the clean inlet, and the compressor peak efficiencies for inlet distortions of 6×12 degrees and 6×24 degrees are about 3.5%, and 9.2% lower than that for the clean inlet, respectively. Further, two kinds of multi distortion area both reduce the compressor stability, and the stall margin improvements of −2.93% and −6.11% are provided by inlet distortions of 6×12 degrees and 6×24 degrees, respectively. The flow field analyses show that the flow conditions of the rotor tip inlet upstream deteriorate after the application of multi distortion area. The values of axial velocity and flow angle of incoming flows in some regions, which are near the shroud, become small due to the adverse effect made by the inlet distortion. So, the circulation capacity of the regions becomes low, and inlet blockages appear in some rotor tip passages. The bigger the distorted range is, the greater inlet blockages and corresponding flow losses are. When multi distortion area changes from 6×12 degrees to 6×24 degrees, there are obvious separations of the boundary layer near the blade suction surface in some blade tip passages, and the serious separations prevent the incoming flows from entering the blade tip passage. As a result, overflows occur at the leading edge of the blade tip. Furthermore, as the number of the distortion generator increases by a factor of one, the effects of inlet distortion on the amplitudes of the air relative velocity and static pressure in the rotor inlet upstream at the distortion generator passing frequency of 1076.5 Hz increase by a factor of about one.

In developing wettable TiB2-based cathodes for Al production, the main problem encountered for decades is the difficulty to sinter or melt this refractory material. Here, suspension plasma spray (SPS) is used as this process makes it possible to use micrometric TiB2 particles to favor a high heat transfer per particle. In addition, an argon gas shield is used to protect the inflight TiB2 particles from oxidation with air during spraying. Our results confirm the efficiency of the argon shroud to limit TiB2 oxidation when compared with a TiB2 coating obtained without shroud. The SPS TiB2 coatings show a good adhesion to the graphite substrate. However, their high porosity indicates an insufficient TiB2 melting during the spraying, suggesting that the transit time spent by the TiB2 particles in the plasma is too short. The SPS TiB2 coatings present a good wettability for molten Al. However, Al infiltration through the porous coating results in the direct contact of molten Al with the graphite substrate, which may be detrimental for its mechanical integrity.

The tip leakage flow in different axial gaps is numerically investigated based on the Reynolds-Averaged Navier-Stokes equations and k-ω SST turbulent model using commercial CFD software ANSYS Fluent. The characteristics of vortexes in the flow field of tip seal and the distribution law of rotor tip leakage loss are analyzed under the change of axial gap. The results show that the flow field in the blade tip seal undergoes complex changes with the increase of axial gap. There are two opposite vortices in the seal cavity with small axial gap, namely, the large vortex in the cavity and the small vortex near the wall of the shroud. The small vortex gradually disappears with the increase of the axial gap. When the axial gap is increased to a certain value, the reverse large vortex is formed in the cavity behind the low teeth of seal, and the leakage rate increases significantly; the steam flow angle and the mixing loss also show different changes. Based on the traditional calculation formula of tip leakage rate, a more accurate calculation formula of tip leakage rate is constructed by introducing equivalent labyrinth seal teeth to consider the variation of axial gap.

Centrifugal pump often operates at different working flow rates to meet engineering requirement. To better reveal the transient behavior of centrifugal pump in the process of decreasing flow rate, the finite volume method (FVM), RNG k-ε turbulence model, sliding mesh technology, and user-defined functions (UDF) were employed to simulate the three-dimensional unsteady viscous incompressible flow in a low-specific-speed centrifugal pump during the abrupt valve-off period. The results show that the differences are very obvious between transient and quasi-steady calculations. The velocity is maximum on the wall of hub and shroud, while the velocity is minimum and uniform distribution at middle positions. The transient flow field lags behind the quasi-steady flow field, which may be related to the reasons; namely, kinetic energy cannot convert pressure energy in time.

Gaps in compressors are generally unfavorable because they lead to energy loss. However, gaps on diffuser blades can broaden the operation range of a compressor. To broaden the operation range of a centrifugal compressor with a tandem diffuser, gaps with different sections and widths on the diffuser blades were examined to determine their influence on the compressor performance. The results show that the compressor’s surge margin increased from 33.28% to 49.2% for a 2.5% tip gap ratio, while its stability margin increased from 44% to 60.5%. However, pressure ratio and efficiency losses of 1.16% and 1.14%, respectively, were incurred. Gap widths less than 5% of the height of the diffuser blade are adequate for broadening the operation range, whereas gap ratios greater than 5% cause more energy loss without broadening the operation range further. Gaps can also reduce the Mach number in the diffuser blade channels and can be influenced by the impeller-tip gap. Moreover, diffuser gaps on the shroud side yield better performance than those on the hub side. An experiment was conducted to investigate the reliability of the calculation and conclusions in this study, and the results proved that the conclusions are valid for different types of centrifugal compressors.

Objective: This paper presents a comparative study of computational fluid dynamics (CFD) simulations and in vitro hemolysis examinations of a bearingless centrifugal blood pump. The outcomes of the in vitro study are analyzed with the help of CFD hemolysis models. Methods: Several pump prototypes were manufactured and tested. Each model was implemented in a CFD framework and simulated with different Eulerian hemolysis models. The outcomes are compared to experimental data. The model achieving the highest correlation is used to explain the in vitro outcomes in detail. Results: It is shown that a double-stage model achieves the best correlation. The sensitivity of the simulation is considerably lower than that of in vitro tests. The CFD model reveals that most of the cell destruction is caused in the radial gap of the pump. Further critical regions are the bottom volume and the shroud clearance gap. Only 0.5% of the priming volume is subject to overcritical shear stress. Conclusion: Cell compatibility can be improved by increasing the radial gap, lowering the shroud and hub clearance gaps, and increasing the fillet radius of the inlet nozzle. CFD models can be used to examine the cell damage effects and help to further improve the pump design. Significance: This paper compares different Eulerian CFD hemolysis models, parameter sets, and equivalent shear stresses to several in vitro hemolysis tests. The sensitivity of the models is compared to that of in vitro studies. It is shown that CFD simulations have their limitations but can help with interpreting the outcomes of in vitro studies.

Variable-pitch multifinned seals (VPMS) have not hitherto found wide use in the steam turbines produced in Russia, although they are quite often used outside of Russia. In modernizing the existing and designing new steam turbines, rotor blades with an integrally machined shroud are used, which opens the possibility to manufacture multirow peripheral seals. In this connection, the question about selecting the optimal VPMS configuration becomes of important practical significance. The results obtained in this study made it possible to experimentally estimate the extent to which different combination of fin pitches on the rotor and stator influence the VPMS discharge characteristics and to elaborate practical recommendations on using them. The minimal leak flow was recorded for the VPMS models with a 2-mm-wide pitch on the rotor. Comparative experimental investigations of VPMS models with 3- and 4-mm-wide spacers on the rotor and 4- and 5-mm-wide spacers on the stator were carried out as applied to the shroud seals of large-capacity steam turbines. The model pair with the 4- and 5-mm-wide spacers on the rotor and stator, i.e., with the pitches equal to 4.8 and 5.8 mm on the rotor and stator, respectively, can be regarded as the most optimal of those investigated in this work. It has been shown experimentally that, with all other things being equal, the leak in VPMSs is by 22–25% smaller than it is in straight-flow seals. By using VPMS, it becomes possible to avoid rubbing of the rotor against the stator under the conditions of relative radial and axial rotor displacements in transient modes of operation. In addition, the aerodynamic forces in VPMS able to excite a low-frequency shaft line self-oscillation are approximately equal to 60% of the similar forces occurring in the conventional radial clearance seals. In view of this circumstance, VPMS can be recommended for use instead of the standard tip shroud seals in the high- and intermediate-pressure cylinders in new and modernized steam turbines.

In this study, nanostructured WC-12Co powder was produced by ball milling and then agglomerating by spray drying. The produced nanostructured WC-12Co powder was used for laser cladding of AISI 321 stainless steel substrate. In order to evaluate the effect of argon shroud protection, the cladding process was performed with and without argon shroud protection. Microstructural and phase characterization showed that argon shroud protection can reduce the WC decarburization and the relative fraction of WC phase in clads reached up to 74%. In addition, microhardness and porosity percentage of the clads with argon shroud protection showed a significant improvement in comparison with the clads without argon shroud protection. The microhardness (to 2200 HV) and wear resistance increased and the porosity percentage decreased to less than 1%.

Despite its long title, White as the Shroud is all about snow and ice, and a little-known war concerning the Siachen Glacier. Then factor in crevasses, avalanches, altitude sickness, snow blindness...

In steam turbine, turbine blades are prone to vibrate during operation, resulting in steam turbine accidents. The most common method for reducing the vibration of steam turbine blades is to design an integral shroud for blade which is termed as integral shroud blade. Most previous studies simplified straight integral blades into cantilever beam and used harmonic response analysis method to simulate the vibration response of blades. This method is suitable for simulating straight blade vibration under harmonic force conditions. For twisted blades, accurate results are hard to acquire and the specific collision process cannot be simulated. In order to observe the collision process on a microscopic scale and explore its collision damping mechanism, this study evaluated the collision process of twisted blades with different integral shroud clearance distance based on LS-DYNA software. The collision process for a two-blade system and a three-blade system with integral shroud clearance distance from 0.1 mm to 0.5 mm has been simulated. The results indicated that integral shroud clearance distance have opposite vibration damping effect when the blade under the condition of forced vibration and free vibration. For the two-blade system, the optimal integral shroud clearance distance is 0.4 mm for forced vibration condition and 0.1 mm for free vibration condition. For the three-blade system, the optimal integral shroud clearance distance is 0.1 mm for forced vibration condition and 0.5 mm for free vibration condition.

In this study, for the first time, ZrC coating was deposited on SiC coated graphite by optimized atmospheric plasma spray (i.e. solid shielding shrouded plasma spray (SSPS)) method. Then SSPS-ZrC c...

In this paper, the effects of shroud movement on transonic flow and heat transfer in the vicinity of turbine tip was studied by using 3-D simulation of GE-E3 first-stage high pressure turbine. Aerothermal performance and flow structure were analyzed with and without turbine shroud moving, respectively. Based on the distribution of limiting streamlines and the vortex structures, the influential characteristics between the leakage flow and the secondary flow generated by shroud movement were studied. Moreover, the coefficient of heat transfer at the wall was investigated. Results show that the flow structure is changing with the movement of turbine shroud, and the location of the separation-line changes significantly by the influence of the secondary flow. The leakage vortex initial location delayed in axial direction and its breakdown point located at 65% cross-section. This accelerates the mixing loss and increase the perturbation. In addition, it is observed that the coefficient of average heat transfer is increased obviously by 54.8% in the region of shroud surface. However, this coefficient in the region of suction surface decreased by 11.9%.

A steam prime mover with rotary motion of the driving element, or rotor, and continuous operation. It converts the thermal energy of steam into mechanical work. The steam flow proceeds through directing devices and impinges on curved blades mounted along the periphery of the rotor. By exerting a force on the blades, the steam flow causes the rotor to rotate. Unlike the reciprocating steam engine, the steam turbine makes use of the kinetic rather than the potential energy of steam. The performance of the turbine depends on the efficient conversion of steam enthalpy into mechanical power with minimum flow losses. In order to reduce the leakage loss hub/shroud sealing between the stages is considered. The hub/shroud sealing improves the performance of the turbine and higher power is generated from the stages. To simulate the hub/shroud sealing, blades & seals are modelled and meshed separately. The bladed region and hub/shroud seal region are attached by General Grid Interface. The flow domain and mesh generation for seal area needs to be accurate to get the correct interface with blades.

Parametric design analysis for Eccentric Rotated Ellipsoid (ERE) shroud profile is conducted whereas the design model is validated experimentally. A relation between shroud inlet, length and exit diameter is established, different ratios related to the wind turbine diameter are introduced, and solution for different ERE family curves that passes on the inlet, throat, and exit points is studied. The performance of the ERE shroud is studied under different wind velocities ranging from 5–10 m/s. The method used in creating the shroud profile is by solving the ERE curve equations to generate large family of solutions. The system is modeled as axisymmetric system utilizing commercial software package. The effect of the parameters; shroud length, exit diameter, inlet diameter, turbine position with respect to the shroud throat, and wind velocity are studied. An optimum case for each shroud length, exit diameter and location of the shroud with respect to the wind turbine throat axis are achieved. The simulation results show an increase in the average wind velocity by 1.63 times of the inlet velocity. This leads to a great improvement in the wind turbine output power by 4.3 times of bare turbine. One of the achieved optimum solutions for the shroud curves has been prototyped for experimental validation. The prototype has been manufactured using 3D printing technology which provides high accuracy in building the exact shape of shroud design curve. The results show very good agreement with the experimental results.

Purpose This study aims to complete the optimization design of a centrifugal impeller with both high aerodynamic efficiency and good structural machinability. Design/methodology/approach First, the design parameters were derived from the blade loading distribution and the meridional geometry in the impeller three-dimensional (3D) inverse design. The blade wrap angle at the middle span surface and the spanwise averaged blade angle at the blade leading edge obtained from inverse design were chosen as the machinability objectives. The aerodynamic efficiency obtained by computational fluid dynamics was selected as the aerodynamic performance objective. Then, using multi-objective optimization with the optimal Latin hypercube method, quadratic response surface methodology and the non-dominated sorting genetic algorithm, the trade-off optimum impellers with small blade wrap angles, large blade angles and high aerodynamic efficiency were obtained. Finally, computational fluid dynamics and computer-aided manufacturing were performed to verify the aerodynamic performance and structural machinability of the optimum impellers. Findings Providing the fore maximum blade loading distribution at both the hub and shroud for the 3D inverse design helped to promote the structural machinability of the designed impeller. A straighter hub coupled with a more curved shroud also facilitated improvement of the impeller’s structural machinability. The preferred impeller was designed by providing both the fore maximum blade loading distribution at a relatively straight hub and a curved shroud for 3D inverse design. Originality/value The machining difficulties of the designed high-efficiency impeller can be reduced by reducing blade wrap angle and enlarging blade angle at the beginning of impeller design. It is of practical value in engineering by avoiding the follow-up failure for the machining of the designed impeller.

Wind-lens turbines (WLTs) exhibit the prospect of a higher output power and more suitability for urban areas in comparison to bare wind turbines. The wind-lens typically comprises a diffuser shroud coupled with a flange appended to the exit periphery of the shroud. Wind-lenses can boost the velocity of the incoming wind through the turbine rotor owing to the creation of a low-pressure zone downstream the flanged diffuser. In this paper, the aerodynamic performance of the wind-lens is computationally assessed using high-fidelity transient CFD simulations for shrouds with different profiles, aiming to assess the effect of change of some design parameters such as length, area ratio and flange height of the diffuser shroud on the power augmentation. The power coefficient (Cp)is calculated by solving the URANS equations with the aid of the SST k–ω model. Furthermore, comparisons with experimental data for validation are accomplished to prove that the proposed methodology could be able to precisely predict the aerodynamic behavior of the wind-lens turbine. The results affirm that wind-lens with cycloidal profile yield an augmentation of about 58% increase in power coefficient compared to bare wind turbine of the same rotor swept-area. It is also emphasized that diffusers (cycloid type) of small length could achieve a twice increase in power coefficient while maintaining large flange heights.

The tip leakage cavitation phenomenon observed in axial-flow type turbines is one of the major causes of blade tip erosion. This study is focused on the Kaplan turbine cavitation occurring at the tip clearance gap between the blade tip and the stationary shroud casing. An unsteady multi-phase cavitation numerical model is studied on a three-dimensional real scale turbine model for five on-cam conditions. The tip leakage cavitation appeared for the optimum cam condition and at high flow rates. The installation of an Anti-Cavity Fin (ACF) on the suction side along the runner blade tip is investigated for its cavitation mitigation functionality. The hydraulic performance, blade loading distribution, vapor volume fraction and tip leakage flow are compared between the blades with and without an ACF. Detailed flow physics on the formation of Tip Leakage Vortex (TLV) and cavitation zones for three on-cam conditions oriented in high flow rates are also presented. The ACF is shown to be effective in decreasing the cavitation intensity at the leading edge without altering the turbine hydraulic performance. A modification of ACF shape at the trailing edge is suggested to avoid damage to the turbine blade and the ACF.

A pressure regulator in a system of the base shroud failed during service. The pressure regulator is intended to regulate the inlet pressure of 275 to 50 kg/cm2 outlet pressure. The working medium is stated to be nitrogen gas. On disassembly of the system, a brown layer was observed on the seating surface of poppet of the main regulator. A brown layer was also observed on the spring pocket and on the spring end surface which was in contact with the poppet. Metallographic tests and hardness measurement were carried out on the components to reach to the cause of failure. The poppet of the pressure regulator failed to function in service due to rusting of its seating surface by crevice corrosion and partial closure of the holes. The crevices at contact surface between the poppet and the spring seems to have formed by settlement of a stagnant condensed moisture along the surface. Partial closure of the holes was due to the presence of condensed moisture as well as rust. Spring made of AISI 302 austenitic stainless steel did not corrode at all, while poppet made of AISI 420 martensitic stainless steel corroded heavily.

For the inverse designs of centrifugal and mixed-flow pump impellers, clarifying the generation process of secondary flows and putting forward corresponding suppression measures is an important approach to improve the impeller performance. In this paper, to provide a better qualitative insight into the generation mechanism of secondary flows in the impeller, a simple kinematic equation is derived based on the ideal assumptions, which indicates that the potential rothalpy gradient (PRG) is the most important dynamic source that actively induces secondary vortical flows. Induced by the natural adverse PRG on the S1 and S2 stream surfaces, two typical secondary flows, H - S and P-S secondary flows, are clearly presented. To specially suppress these typical secondary flows, a general alternate loading technique (GALT) is proposed, aiming to adjust the real blade loading δp to control the PRG features. At the blade fore part, the δp on the hub streamline should be slowly increased to avoid breakneck growth of the potential rothalpy to reduce adverse streamwise PRG on the S2 streamsurface. At the blade middle part, the δp should be moderately decreased to reduce adverse streamwise PRG on the S1 streamsurface. At the blade aft part, the difference in the δp between the shroud and hub streamlines should be decreased faster to control the exit uniformity. By applying the GALT to the impeller designs of three typical pump types in hydraulic engineering, the organizational effect of the PRG on fundamental flow structures is proven. The GALT can effectively control the PRG distributions and suppress the secondary flows, thereby widening the pump’s high-efficiency zone, improving flow uniformity and suppressing pressure fluctuations. Compared with the current Z-G method and the ALT, the GALT can meet the requirements of “de-experience” better, thereby enabling the designers to obtain good products explicitly and quickly.

The research is concerning two unusual evidences of the late Medieval art, which could be seen in the Museum of the cathedral St. Stephan in Vienna. Both of them are related to Herzog Rudolf IV of Austria (1358 - 1365). One artefact in the museum is his silk gold woven shroud elaborated with especial mastership from Chinese silk in Tabriz, a city in present Iran. Especially important for this fabric is that thanks to the interwoven name of the ruler it could be dated precisely. The road of this Near East fabric to Europe and to the tomb of the Herzog in Vienna could be reconstructed. Rudolf IV died suddenly during the visit to his relative Bernabo Visconti in Milano who was one of the richest men in Europe by that time. Probably the fabric was brought across the Silk Road to Constantinople and further across the sea to Genova and to the city of silk Lucca and then to Milano. Such gold woven fabrics from the Islamic world could be found not rarely in the European ruler’s tombs. The second unusual object in the cathedral museum is a portrait of the Herzog. So far this portrait was attributed to a Prague artist. But it could be proved that it originated from Upper Italy and probably was painted by an artist from Verona who was associated to the society around the great humanist Francesco Petrarca. This portrait rises the question about the emergence of early ruler's portraits in Eu-rope and in this aspect is also related to achievements of the „Palaeologus Renaissance“ art in South – East Europe. The two objects are considered as expression forms of the ruler’s funeral culture of the late Medieval age. In the context formed by the comparative approach new possibilities for analysis are created which cross over the traditional methodology of History of Art.

The results of the development of a new ceramic-metal composite material for seals of the steam path of steam turbines are presented. The concept of the new material and a model of its performance when rubbing against blade fins are developed. Data on its structure, physical and mechanical properties, and pilot operation as part of shroud seals of an experimental steam turbine, as well as commercial turbines of different capacity, are presented.

For the compressor with shrouded stator blades, the stator well is a rotor-stator space between the rotating drum and the stationary shroud. Due to the pressure difference, a reverse leakage flow would travel through the stator well and inject into the main flow path. Although, the labyrinth seal is commonly placed under the shroud, the rotation effect and seal clearance variation in actual operation process have great impact on the characteristics of this inter-stage leakage, as well as the compressor performance. In this paper, experiments were conducted at a compressor inter-stage seal test rig. The leakage flow rates, total temperatures and swirl ratios were obtained at different speeds and working clearances. The proportions of rotation effect and the clearance reduction effect were analyzed by data processing. Comparisons indicate that the working clearance and leakage flow reduce about 43% and 50% respectively, when the rotational speed ω=8100 r/min. The proportion of reduction caused by the rotation effect is around 15%, while the influence of working clearance variation is much greater, accounting for about 35%. The windage heating coefficient and swirl ratio in the outlet cavity are almost in exponential relationship with the rotor speed. The increases in total temperature and swirl ratio generated by the rotation effect are found to be about 80%. In addition, the swirl and radial velocity profiles in the cavities were discussed by validated numerical simulations to reveal the typical flow characteristics. The data presented can provide guidance for better leakage conditions prediction as well as the inter-stage seal design enhancement.

Reverse flow has a detrimental effect on the stable and safe operation of centrifugal pumps. To study the formation mechanism and suppression of the reverse flow, a semi-open centrifugal pump with circumferential groove in the shroud was simulated. Then, the flow field and pressure fluctuation were analysed. The absolute flow angle at the blade inlet nearing the shroud was close to 180° because of the joint action of the leakage flow and blade inlet impact under low flow rate. This phenomenon resulted in the formation of a low-speed region and the reverse flow and low-frequency pressure fluctuation. The circumferential groove provided a channel for the leakage flow, which could quickly pass through the groove, and reduced the absolute flow angle at the blade inlet nearing the shroud and weakened the trend of the tip leakage flow to upstream. The low-frequency pressure pulsation was eliminated, and the amplitude of the blade passing frequency was reduced under 0.7 Qd (Qd is the design flow rate). The reverse flow thickness coefficient became zero with the circumferential groove. The proportion of the reverse flow volume to the volume of inlet pipe decreased from 14.7 % to 2.2 % under 0.4 Qd. This research indicated that the circumferential groove arranged in the shroud could effectively suppress or eliminate reverse flow.