Pressure Side Of Blade Research Articles

Оценка параметров текстуры прецизионных поверхностей с применением квазиоптимальных корреляционных алгоритмов

The authors considered a new method of texture analysis of machined precision surfaces based on using computer optics and the autocorrelation method of processing the images of micro-relief textures under the study. This method is based on a probabilistic comparative evaluation of the unknown texture of the micro-relief under the investigation with the available textures of reference micro-patterns, in which microrelief parameters are determined. The paper proposes an approach to identify the profile surface roughness of a gas turbine engine (GTE) blade after vibro-contact polishing according to the parameters of correlation surface texture. The authors studied the surface micro-geometry of the blade back and pressure side using the optoelectronic complex based on the calculation of the average amplitude of the variable component of an autocorrelation function resulting from computer processing of a surface video image. The application of the electrooptic method for evaluating the surface texture of compressor and turbine blades allows building the surface roughness fields and more deeply analyzing the technology of final processing of the GTE blade feather profile. The relevance and novelty of the study lie in the promising technique to evaluate the surface quality parameters using the electrooptic method. A special feature of this method is the measurement of surface area roughness, while the stylus methods measure the roughness of the surface profile. An important advantage of the proposed method is its application to measure the roughness parameters of a curved surface by a non-contact method, which is advanced since there are surfaces of parts that do not imply being scratched with a diamond needle.

Film cooling simulation on an entire gas turbine blade with square pulsed coolant injection

Film cooling is an effective method to keep the gas turbine blades from high temperature gases and thermal stresses. Square pulsating film cooling on different sections of a modified NASA C3X blade is numerically investigated. Temperature distribution and film cooling performance are investigated for various blowing ratios of 0.5, 0.75, 1.0, 1.5, 2 and 2.5 in pulse frequency of 50Hz. Reynolds-Averaged Navier-Stokes equations for steady and pulsating injection considered. The shear stress transport ( ) model applied for turbulence effects. Simulations are performed using finite volume method. Obtained results show different findings of pulsating film cooling on the various blade surfaces. For large blowing ratios, averaged pulsed film covering effectiveness at leading edge and pressure side of blade is reduced compared to small and middle values of blowing ratios. This trend is reversed in the suction side. Reynolds number of mainstream has the maximum effect on film effectiveness distribution on pressure section. The averaged centerline pulsed film coolant performance on the pressure surface and leading edge at blowing ratio of 0.5 and for suction side at blowing ratio 2.5 was maximum.

Numerical investigations of flow characteristics of a pumpjet propulsor in oblique inflow

In this study, a detailed analysis of hydrodynamic performance of a pumpjet propulsor (PJP) in different oblique inflow angles (β=0⁰, 5⁰, 10⁰, 15⁰, 20⁰, 25⁰, 30⁰, 40⁰) and different rotational speeds (n=3000rpm, 3600rpm, 4200rpm) is investigated numerically. The SST k-ω turbulence model and sliding mesh technology based on the Reynolds Averaged Navier-Stokes (RANS) method are employed. The structured grids are adopted to the whole computational domain. The grid independent inspection is carried out and verified. A ducted propeller (the Ka4-70 propeller in 19A duct) is selected to validate the numerical method by comparison of its results with experimental data. Based on the numerical method, it can be found that the propulsor efficiency decreased with the increasing of different β. The propulsor efficiency changes tinily in little oblique angle and decreases significantly when the oblique angle is larger than 20⁰. The thrust coefficient and torque coefficient of PJP are obtained. The increase of β has a negative impact on the balance performance of PJP. The pressure distributions of pressure and suction side of rotor blade with different β are analyzed. Owing to the influence of β, the pressure of the upper left region of rotor blade drops significantly. The enlargement of the local load on pressure side and the appearance and expansion of the low-pressure region on suction side occour at the bottom right region of rotor blade. The radial distributions of the axial velocity (Vz) and the tangential velocity (Vt) with different Span and β along the axial direction are investigated. The increase of β resultes in a severe oscillatory behavior of the flow velocity, which easily induces the occurrence of cavitation phenomenon and mechanical vibration. The velocity contours of the axial cross section with different β are presented. Due to the change of β, the flows are blocked by the flow-guide and duct, there are obvious high-velocity and low-velocity regions of the flows.

A numerical study on mechanisms of energy dissipation in a pump as turbine (PAT) using entropy generation theory

Abstract The utilization of pumps in reverse function is one of the economically beneficial methods for off-grid power generation in micro-hydropower capacities. The traditional method of hydraulic loss calculation in turbomachinery based on pressure drop calculations is unable to determine the exact location of losses. In this paper, the irreversible energy losses within the PAT has been studied for the first time using entropy generation theory and the second law of thermodynamics point of view. In order to conduct numerical simulation, the 3-dimensional incompressible steady-state flow within the PAT is simulated by solving the Reynolds averaged Navier-Stokes (RANS) equations. The shear stress transport (SST) turbulence model is considered for turbulence modeling. The quantity of direct (viscous) and turbulent entropy generation rate is calculated in different PAT components in 9 different flow rates in the range of 0.7QBEP to 1.3QBEP. The numerical results show that the turbulent term is the main factor of entropy production within the PAT (86.89%–90.98%), and thus, turbulent entropy generation is the dominant mechanism for hydraulic losses. More than 50% of the energy dissipation occurs within the PAT runner. Most of the losses within the runner take place at the blade leading edge, blade trailing edge and flow separation regions of the blade suction and pressure sides. The volumetric entropy generation rate analysis demonstrates that the draft tube has the most potential to generate irreversible losses among all the components (47.37%). Flow field analysis reveals that the blade inlet shock, flow deviation at the blade outlet, flow separation, backflow and vortices in flow passages are categorized as the main reasons for entropy production and irreversible hydraulic losses within the PAT components. The advantages of the entropy generation method including the determination of the exact location and quantity of energy dissipation within the PAT are indicated in this investigation.

Influence of rotating speed on tip leakage vortex in a mixed flow pump as turbine at pump mode

Tip clearance results in tip leakage flow from blade pressure side to suction side, and further deteriorates the energy performance and operation stability. In the present work, the influence of rotating speed on tip leakage vortex in a mixed flow pump as turbine at pump mode is investigated. As rotating speed increases, the pump head increases according to the similarity law and the best efficiency point shifts towards large flow rate. Meanwhile, the tip leakage flow and axial momentum also increase. A prediction model for separation angle of tip leakage vortex is proposed, and its relative error is below 5%. As rotating speed increases, the oscillating frequency of primary tip leakage vortex increases from 201.92 Hz to 215.60Hz, and the high pressure fluctuation region develops from leading edge to nearly the whole blade-to-blade passage.

Numerical Analysis of High-Altitude Inlet Air on Boundary Layer Flow Loss in an Aero-Engine Compressor

A numerical analysis is performed to explore the high altitude and high Mach flight on the effect of wall boundary layer loss in the compressor. The accuracy for solution results by the application of the similarity criterion and parameter definition of the air inlet is compared with the existing experimental test result. The results indicate that the radial adverse pressure gradient in the rotor domain gradually increases along the span direction and decreases as flight Mach number increases; meanwhile, the circumferential adverse pressure gradient on the pressure side of the rotor blade is correspondingly larger and less than that on the suction side. In particular, the entropy increase along the streamwise shows a decreasing trend and an increasing trend inside the hub and shroud wall boundary layers, respectively. At 2.1 Ma, the entropy increase in the rotor domains enhances by 24.36–27.80% inside the shroud boundary layer, relative to the hub boundary layer; however, it decreases by 0.97–8.54% in the stator domain. With the increase in flight Mach number from 2.1 to 3.4, the average entropy increase reductions in the rotor domain decrease by 18.99–24.97% within the hub boundary layer and 5.71–8.1% within the shroud boundary layer. In the stator domain, it drops by 18.45–9.03% inside the hub boundary layer and 6.88–8.67% inside the shroud boundary layer. It was therefore found that, as Mach number increases from 2.1 to 3.4, the entropy increase reduction is larger inside the hub boundary layer than inside the shroud boundary layer.

Experimental Investigation of a 10 MW Prototype Axial Turbine Runner: Vortex Rope Formation and Mitigation

AbstractThe transient load fluctuations on the runner blades of prototype hydraulic turbines during load variations are one of the main causes of fatigue and eventual structural failure. A clear understanding of the dynamic loads on the runner blades is required to detect the source of the fluctuations. In this paper, an experimental investigation of vortex rope formation and mitigation in a prototype Kaplan turbine, namely, Porjus U9, is carried out. Synchronized unsteady pressure and strain measurements were performed on a runner blade during steady-state and load variation under off-cam condition. The normalized pressure fluctuation during load variations remained approximately within ±0.2Pref for all the pressure transducers installed on the blade pressure side and is even slightly lower during the transient cycle. Higher pressure fluctuations were found on the blade suction side, approximately four times higher than that of on the pressure side. The synchronous and asynchronous components of the vortex rope were clearly observed at the low discharge operating point and transient cycles. The spectral analysis of the pressure signals showed that the synchronous component appears before the asynchronous component during the load reduction, and it lasts longer during the load increase. These frequencies slightly change during the load variation. In addition, the results proved that the strain fluctuation component on the runner blade arises from the synchronous component of the vortex rope at low discharge while the asynchronous component influence is negligible.

Numerical investigation on the effects of leakage flow from Guide vane-clearance gaps in low specific speed Francis turbines

Clearance gap in guide vanes of Francis turbine induces the leakage vortex. This vortex flow interacts with the main flow and leads to the instability in the fluid flow pattern and eventually deteriorates the performance of the turbine. In this study, the detailed numerical examination of the unsteady flow due to leakage vortex and influence of this in the performance of turbine is carried out using time dependent numerical analysis. The numerical simulation is carried out using SST turbulence model with numerical validation. The development of leakage vortex is studied within the clearance gap region. Time dependent numerical simulation is carried out to investigate the growth and vortex propagation considering five revolutions of the runner. Results shows that the leakage vortex travelling form the guide vane clearance gaps influence the performance of the runner. On analysing the leakage vortex path, it is seen that the vortex travels from the pressure side of runner blade to the suction side of adjacent blade opposite to the runner rotation. Furthermore, this leakage vortex is carried down to the draft tube where the vortex rope seems to grow up to 50% geometric progression of draft tube cone and gradually decreases before reaching the elbow. Upon investigation of resulting torque and head during runner rotation, the periodic variation of torque and head can be seen, however with different phase. This is inferred to be the influence of leakage vortex that travels along with the main flow.

Distribution and motion characteristics of bubbles in a multiphase rotodynamic pump based on modified non-uniform bubble model

Multiphase rotodynamic pumps are important equipment that transport gas-liquid mixtures in offshore oilfields, suggesting it is necessary to investigate the flow characteristics in such pumps. In this study, the Eulerian two-fluid model is solved to obtain the bubble distribution in the pump, while the non-uniform bubble model is used to predict the break-up and coalescence of bubbles. The gas cavity equation is introduced to capture the rapid coalescence of bubbles near the suction side of the impeller blades, and the interphase forces in the cavities are modified. Compared with the experimental measurements for the gas volume fraction and bubble size, it is found that the simulations with the modification have better accuracies than without it. The effects of the inlet gas volume fraction (IGVF) on the bubble distribution are analyzed. Due to the formation of vortices, a large bubble number density is observed near the shroud of the impeller inlet, which increases with greater IGVF. The gas-liquid separation in the diffuser becomes more significant as the IGVF increases. Bubbles from the impeller inlet are observed to continuously gather near the suction side of the impeller blades. This forms a gas cavity that moves towards the impeller outlet with a low gas volume fraction. The rotor-stator interactions cause the air pockets to discontinuously move along the pressure side of the diffuser blade.

Numerical Study of Rotor–Stator Interaction of a Centrifugal Pump at Part Load With Special Emphasis on Unsteady Blade Load

Abstract Three-dimensional (3D) unsteady Reynolds-averaged Navier–Stokes (URANS) flow simulations are conducted to investigate the highly unsteady flow field at part load operation of a centrifugal pump. By the availability of unsteady flow field measurement data in the impeller wake region, a thorough validation of the simulation method is performed. Grid independence of the results is ensured. Unsteady characteristics in terms of head and shaft power as well as transient blade loads are evaluated to assess the unsteady pump performance. Significant mis-loading of the blading is revealed when one blade passes the volute tongue and associated with the strong unsteady and 3D flow field in the impeller-volute tongue region. Negative radial velocity in the tongue region is the origin of a vortex at the blade pressure side and a subsequent pressure drop that leads to even temporally negative blade loading. The results provide a detailed insight in the complex part load flow field that might be utilized for an improved pump design. As a valuable secondary outcome, a comparison of results obtained by two widely used computational fluid dynamics (CFD) codes for pump flow simulation is provided, i.e., the commercial code ansyscfx and the branch foam-extend of the open source software openfoam. It is found that the results of both methods in terms of unsteady characteristics as well as local ensemble-averaged velocity field are consistent.

Numerical analysis of the vortical structure and its unsteady evolution of a centrifugal pump

To investigate the complex flow and vortical structure of a centrifugal pump with low specific speed, the numerical simulation approach DDES is used to capture the unsteady flow fields when the blade periodically sweeps the volute tongue. Attentions are attracted on unsteady vortical structures on the mid-span of the model pump, and quantitative data of z-vorticity(axial component of vorticity) at the impeller exit are extracted to discuss the corresponding evolution process. Besides, three dimensional vortices within the impeller are also identified at different working conditions. Results show that at the nominal and high working conditions, evident vorticity sheets are generated within the pump. High vorticity sheets are developed on the blade suction side and the trailing edge, which are also significant in the volute area caused by the vortex shedding from the impeller. The interactions between the shed wake flow and the tongue are not identical at various working conditions, and it is more evident at high working condition. With the blade moving away from the tongue, high vorticity is generated around the blade suction side. Especially at high working condition, several vorticity sheets with alternative negative and positive values are formed near the blade suction side. The vorticity sheet tends to stretch towards the blade pressure side with the impeller passing the tongue. Based on the 3D vortical structures, it is found that the hairpin vortices are generated within the blade channels, which could not be captured at low working condition. Finally, the obtained vorticity sheet and 3D vortex results will contribute to the understanding of the complex flow structures in pumps.

DDES analysis of unsteady flow evolution and pressure pulsation at off-design condition of a centrifugal pump

In the present paper, to investigate unsteady flow structures and pressure pulsations at off-design conditions, a low specific speed centrifugal pump is investigated by the DDES (Delayed Detached Eddy Simulation) method. Emphasis is laid on the unsteady evolution of flow structure and pressure pulsation at the stalled condition. Results show that the jet-wake flow pattern could be captured by the current numerical simulation method, and it shows a high calculation precision for the jet flow. Relative velocity decreases rapidly in the wake region towards the blade suction side. Significant inflection point exists between the jet and wake flow regions, and it almost keeps unchanged at the identical impeller-volute position under various flow rates. At the stalled status, the inflection point moves towards the blade pressure side with the blade passing the volute tongue, and evident non-uniform flow distributions are formed in the blade channels characterized by the multiple vortices. The blade channel is gradually blocked by the corresponding stall cell when the blade approaches the volute tongue, and it indicates that the volute tongue has a significant effect on the evolution process of the stall structure. By combination analysis of the unsteady evolution of the stall structure and pressure spectrum, the stall frequency at 0.25fn (being fn the impeller rotating frequency) is captured for the current model pump.

Gas-liquid two-phase flow in the axial clearance of liquid-ring pumps

In this study, the leakage flow in the axial clearance of a 2BEA-203 liquid-ring pump has been modeled through numerical simulation using the renormalization group k - ∈ turbulence model and the multiphase volume of fluid method. Numerical results show that the axial leakage flow reduces the inlet vacuum and efficiency of the liquid-ring pump. The gas-liquid two-phase flow within the axial clearance region is completely separated. Several droplets are scattered outside the suction region, some of which flow back into the low-pressure suction region along the wall of the suction port. Given the axial asymmetry of the flow passage, the phase distribution within the impeller region is non-uniform along the axial direction. The numerically simulated pressure distribution within the axial clearance region accords well with the vortex distribution caused by the leakage flow. The leakage flow interacts with the impeller flow, and forms a corner vortex near the pressure side and a leakage vortex near the blade suction side. As the relative coordinate of the cross planes to the blade (sc−1) decreases from tip to hub, the corner vortex near the blade pressure side gradually weakens while the leakage vortex near the suction side gradually strengthens. These vortices mostly form in the suction and compression zones of the clearance region and significantly affect the overall pump efficiency. Findings of this study reveal the flow structure in the axial clearance of the liquid-ring pump and the interaction between the leakage and main flow.

Multi-Parameter Optimization and Analysis on Performance of a Mixed Flow Pump

A mixed flow pump with guide vanes was chosen as research model in this study, and eight parameters of the impeller were selected as optimization variables, including blade outlet inclination angle, blade wrap angle at hub, blade inlet angle and outlet angle at middle stream line, blade outlet width, front shroud inclination angle, hub inclination angle and vane number. Firstly, orthogonal experimental method and CFD numerical simulation method were used to produce samples, then the RBF neural network was adopted to establish the performance prediction model as the objective function, multi-island genetic algorithm was used for solving the objective function at last. Based on all the above, a method of multi-parameter optimization method on energy performance of mixed flow pump without changing the nominal diameter of impeller outlet was proposed and then verified by experiments. By this method, the pump head and efficiency at the design point of the model pump were increased by 11.5% and 4.32%, respectively. Meanwhile, the peak value of pressure pulsation coefficient at pump inlet, impeller outlet, guide vane outlet and pump outlet all decreased obviously, by a maximum decrease of 62.9%. Compared to the original model, the static pressure in the optimization model increased by 30kPa and the gradient of static pressure distribution after optimization becomes larger and more uniform. The turbulent energy intensity at the impeller outlet was reduced by 0.2m2/s2. The pressures at the 60% blade position and 80% blade position both increased by nearly 65kPa and the pressure decreased by 50kPa at the blade pressure side.

Investigation of Uniformity of Allowance along Airfoil of GTE Turbine Blade

This paper shows the results of a study of the uniformity of the allowance along the airfoil in the turbine blades workpieces. It is found that in the existing industry, there is a defect associated with a lack of allowance along the airfoil (from the blade back and pressure side) for the polishing operation in order to give the required cleanliness and roughness of the surface layer. By measuring the wall thickness of the blade airfoils, it is concluded that by mechanically modifying the technological bases on the blade, it is possible to select the optimal position of the workpiece in the template instrument, at which the allowance along the airfoil is relatively uniform, and the dimensions of the blade wall thickness will be within the specified tolerance.

Formation of film cooling on the turbine blade back and pressure side in the case of using V-shaped dimples

Alongside the development of methods of intensifying convective heat transfer inside the blade, development of methods of local improvement of the efficiency of film cooling of the blades surface is still of immediate interest. The film is formed on the blade surface in conditions of high-camber shape and low initial velocity of the gas flow in the vicinity of the leading edge with its subsequent abrupt acceleration. The paper presents some data on the peculiarities of film formation on the back and pressure side of the blade in the vicinity of the leading edge. Experimental temperature distribution over the adiabatic wall was obtained with the use of a FLIR-E 64501 thermal imager. It was found that the conditions for the film formation on the blade back are more favorable than those on the pressure side. It manifests itself in the fact that optimal blowing parameters on the blade back are considerably lower than those on the pressure side. The use of V-shaped dimples located on the wall immediately behind the holes for blowing was suggested as a measure for local improvement of film cooling efficiency. The efficiencies of film cooling in the formation of a curtain, without the use and with the use of V-shaped dimples behind the holes for blowing were compared. Local improvement of efficiency and uniformity of film cooling distribution with the use of V-shaped dimples behind the holes for blowing was observed.

Effects of flow pattern on hydraulic performance and energy conversion characterisation in a centrifugal pump

An experimental investigation based on particle image velocimetry (PIV) technology was used to measure the internal flow in a low-specific-speed centrifugal pump impeller. The main purpose of this paper is to quantitatively study the influence of the internal flow patterns on the hydraulic performance and energy conversion characteristics through this visualization experiment. The PIV measuring region covers full impeller channels. Phase-averaged relative velocity distributions were calculated to investigate the evolution of internal flow pattern with the decrease in flow rate. The effect of flow pattern on pump head has also been investigated qualitatively. Results show that a clockwise vortex on the blade suction side and a counterclockwise vortex on the blade pressure side will appear in different impeller passages with the decrease in flow rate. The counterclockwise vortex moves towards the impeller outlet, but the clockwise vortex moves to the opposite side. Detailed studies show that the motion of the vortices considerably impacts pump hydraulic performance. The counterclockwise vortex will increase energy losses, whereas the clockwise vortex positively affects the pump head. Moreover, the blade loading distribution and its variation with flow rate are proposed to analyse the energy conversion mechanism in the centrifugal pump impeller.

Theoretical Prediction Model of Tip Leakage Vortex in a Mixed Flow Pump With Tip Clearance

Abstract Tip clearance results in the leakage flow from blade pressure side to suction side, which will further cause the tip leakage vortex (TLV). Moreover, the flow pattern in an impeller is seriously deteriorated due to the TLV and its interaction with the main stream. In this work, the TLV in a mixed flow pump is investigated by numerical simulation validated by experiment measurement. The primary tip leakage vortex (PTLV) trajectory is specially studied with consideration of the tip clearance size δ, the impeller blade number Zi, and the impeller rotational speed n. The results show that δ slightly shifts the separation point (SP) of the PTLV but rarely affects the separation angle α. The increase in Zi and the decrease in n both lead to the shift of the SP toward the blade trailing edge and the decrease in α. Furthermore, a theoretical prediction model is proposed to predict the PTLV trajectory, by which the axial position and radial position of PTLV trajectory versus the rotation angle can be predicted. The proposed model is verified to be accurate to predict the PTLV trajectory, especially for the PTLV trajectory in the main flow passage. The dynamic evolution of TLV under different tip clearance sizes can all be classified into the same three stages: splitting stage, developing stage, and merging stage. Meanwhile, the dynamic evolution frequency fe is the same as the impeller rotational frequency fi.

Structural collapse characteristics of a 48.8 m wind turbine blade under ultimate bending loading

To further study the structural failure mechanism and response characteristics of large wind turbine blades under extreme conditions, a full-scale 48.8 m blade collapse test was carried out. The strong coupling action of different damage modes are descripted by the gradual collapse process recorded by cameras. The damage behavior of suction side and pressure side, and interior and skin behavior of test blade are analysed. The test shows that the buckling of the suction side spar cap at about 21 m and cracks of the root shear web are the essential factor leading to the catastrophic failure of the entire blade, the test result is consistent with the finite element analysis. The load-deformation curve of the suction side spar cap, the deflection curves at 24 m, 36 m and tip, and the strains curves along the blade span are plotted to perform the data analysis. The critical load of 78% and deflection behavior in collapse process are determined by data analysis. The research results have great significance for improving the ultimate strength of entire blade, and provide a theoretical basis for the structural improvement of the weak points of blade.

Effect of cavity depth on thermal performance of a cooled blade tip under rotation

In this paper, the effect of cavity geometry of a squealer blade tip on its thermal performance is investigated. Numerical analyses were performed for three depth-to-width ratios for a cooled squealer tip. Also investigated is the effect of cooling introduction into the flow tip and the effect of rotation via the comparison of stationary and rotational domains where the latter was simulated by rotating the blade. The rotational speed and boundary conditions used in the numerical study are chosen to represent the turbine operating environment. The blade tip used had a cooling configuration consisting of seven holes of the same size located on the tip near the blade pressure side. The study presents a discussion on the flow physics within the tip gap and heat transfer on the blade tip. Film-cooling performance of the considered blade tip geometries is demonstrated using distributions of film-cooling effectiveness. It is observed that both the rotation and the addition of cooling at the tip significantly alter the tip gap flow, which is found to have a strong effect on the blade tip heat transfer. The addition of cooling increased the heat transfer coefficient on the blade tip, while an increase in the rim height resulted in higher film effectiveness since the amount of leakage flow entering the cavity floor was reduced.