Blade Suction Surface Research Articles

Enhancement of OWC Wells turbine efficiency and performance using riblets covered blades, a numerical study

Oscillating water column (OWC) is one of the first devices used for wave energy conversion. This wave absorber converts pneumatic energy to mechanical energy through a Wells turbine. In this paper, the micrometer protrusions similar to shark skin (riblet) were added to the Wells turbine blades to investigate its effect on the improvement of the device performance as well as its efficiency. The flow interaction with Wells turbine was modeled using Star CCM+ software. In this process, the structured grid was used throughout the study domain. The numerical modeling results show that for high flow coefficients, applying riblet on the blade surface results in an increase in the thrust coefficient and a decrease in the blade suction surface pressure. The proposed design significantly improves the pressure distribution around the blade and the separation point, as well as the efficiency of the turbine within the computational range. Another benefit of riblets is the delay and reduction of separation at the tip of the blade. In addition, there is an increase of 18.4% in the torque coefficient and 16.8% in the efficiency of the riblet covered blades in deep fatigue conditions. Furthermore, the results show that in computational range, the Wells turbine demonstrates 2.3% increase in efficiency.

Stall Inception in a Compressor with Subsonic, Transonic, and Supersonic Inlet Conditions

A combined experimental and computational approach has been used to investigate the stall inception mechanisms and subsequent poststall behavior of a single-stage axial compressor running at different operating conditions, determined by its rotational speed. This paper emphasizes differences in the origin of stall inception depending on the associated inlet flow regimes: 60% speed (subsonic), 80% speed (transonic), and 100% speed (supersonic). At all speeds, stall is initiated with spike-type disturbances that develop into full-span rotating stall. This paper demonstrates for the first time that for a single compressor geometry, a variety of mechanisms can be responsible for the sources of the blockage leading to stall inception depending on the rotational speed. At 60% speed, the inlet flow is subsonic and the primary driver is a corner separation forming between the casing and blade suction surface. At 80% speed, the spillage of tip leakage jet ahead of the leading-edge plane combines with a small shock-induced corner separation to cause sufficient total blockage and subsequent stall inception. Finally, at 100% speed, the mechanisms are the same as at 80% speed but with a greater blockage contribution from the corner separation due to a stronger shock creating a larger separation.

Pressure Fluctuation on the Blade of a Axial Fan Driven in a Cooling System Enclosure

W Suppressing the pressure fluctuations distributed on the blade surface of an axial fan is applied as one of the means to reduce the noise generated in the cooling system of construction machinery. For that purpose, it is effective to use computational fluid dynamics (CFD) to capture the 3D vortex structure around a fan blade. However, while there have been many reports on the flow field formed around the blades of a fan alone or an axial fan with a duct-shaped shroud, the influence of the vortex structure formed at the actual operating point of the axial fan on the pressure fluctuation on the blade surface has not been sufficiently discussed. In this study, the three-dimensional vortex structure around the fan blade installed in the cooling system is investigated, and in particular, the influence of the wing tip leakage vortex on the pressure fluctuation on the fan blade surface is clarified. Wing tip leakage vortex that flow from forward in the direction of rotation of the fan interfere with a blade while oscillating periodically in the y-axis direction. The oscillation of the forward wing tip leakage vortex causes the separation position of the newly formed wing tip leakage vortex to change, and as a result, the pressure fluctuation increases at the tip of the blade suction surface near the separation position.

CFD-Based In-Depth Investigation of the Effects of the Shape and Layout of a Vortex Generator on the Aerodynamic Performance of a Multi-MW Wind Turbine

Thick airfoils are conventionally adopted in the blade root region of a wind turbine to ensure structural safety under extreme conditions, despite the resulting power loss. To prevent this loss, a passive flow control device known as a vortex generator (VG) is installed at the starting point of the stall to control the flow field near the wall of the suction surface. In this study, we used computational fluid dynamics (CFD) to investigate the aerodynamic characteristics induced as a result of the shape and layout of the VG on a multi-MW wind turbine blade. The separated and vortical flow behavior on the suction surface of the wind turbine blade equipped with VGs was captured by the Reynolds-averaged Navier–Stokes (RANS) steady-flow simulation. The parametric sensitivity study of the VG shape parameters such as the chord-wise length, height, and interval of the fair of VGs was conducted using thick DU airfoil on the blade inboard area. Based on these results, the response surface method (RSM) was used to investigate the influence of the design parameters of the VG. Based on the CFD results, the VG design parameters were selected by considering the lift coefficient and vorticity above the trailing edge. The maximum vorticity from the trailing edge of the selected VG and the lift coefficient were 55.7% and 0.42% higher, respectively, than the average. The selected VG design and layout were adopted for a multi-MW wind turbine and reduced stall occurrence in the blade root area, as predicted by the simulation results. The VG improved the aerodynamic performance of the multi-MW wind turbine by 2.8% at the rated wind speed.

Optimization study on the influence of little blades’ spatial position on a compressor cascade performance

To reveal the importance of little blades’ spatial position to improve the cascade performance at different condition, the pitchwise and axial direction of the little blades on the end-wall are adopted as the optimization variables to complete a double-objective optimization. Meanwhile, the three-dimensional flow field characteristics of the cascade with and without little blades are analyzed comparatively. The study found that as the optimal solutions are obtained at the three bigger incidences (3°, 5°, and 7°), the optimal position is always close to the leading edge of blade and far away from the blade suction surface, and the more intuitive design suggestions are given in this article. Moreover, at the near design conditions (−1°, 0°, and 1°), little blades increase the total pressure loss and reduce the static pressure, which are considered unsuitable for improving the cascade performance. If the stable operation range are the main performance indicators, the optimization of the little blades’ spatial position should be completed at the near stall condition (7° incidence). If the conditions with mid-range incidences (2°< i <5°) are the main performance index, the parameter optimization of little blades should be achieved at 5°. Based on the further flow field analysis of the optimization results obtained at 3°, 5°, and 7° incidences (named Opt_Act3, Opt_Act5, and Opt_Act7), the induced vortices resist the effect of axial reverse pressure gradient and pass through the blade passage, which is the main reason for the total pressure loss reduction. Appropriate spatial position of little blades not only strengthens the capability to prevent the low-energy fluids accumulating in the corner region near the end-wall, but exhibits sufficient advantage to weaken the boundary layer.

Applications of little blades in a high-load compressor cascade with leaned blade

The development of boundary layer affects the compressor cascade performance to a certain extent. Therefore, the compound lean and little blades are selected to redistribute the boundary layer, and the influences of these two flow control technologies on the axial compressor cascade performance are further studied. The calculated results showed that appropriate high pressure region on the blade suction surface near the end-wall is helpful to reduce the total pressure loss of compressor cascade, which can be achieved by positive lean technique. Meanwhile, the maximum stable operation boundary can be expanded by the application of positive leaned blade. On the other hand, the introduction of negative lean angle not only increases the total pressure loss of cascade, but reduces the stable operation range. As the little blades are introduced in the negative lean compressor cascade, the stable operation range is significantly improved by the introduction of little blades. Especially the cascade with −10° lean angle, the maximum stable operation boundary is increased from 1° to 6°. In the positive lean compressor cascade, although more low-energy fluid is accumulated on the blade suction surface near the mid-span, the little blades still show an active role in reducing the total pressure loss and expending the stable operation range, because the influence range of induced vortex reaches 30%span. The results provide a reference for improving the aerodynamic performance of compressor stator, especially when more low-energy fluid is blocked in the range near the mid-span.

Study on aerodynamic excitation of radial turbine blades with vaneless volute at low excitation order

High cycle fatigue (HCF) of radial turbine blades is one of key issues of turbochargers and it determines the reliability of the device. Most of researches about HCF of radial turbine blades focus on vaned turbines, whereas few investigations have been carried out on vaneless turbines which are widely applied in automobile turbochargers. This paper studies the blade vibration mechanism of a vaneless radial turbine at low excitation order via one-way fluid–structure interaction simulation method validated by experiments. The results surprisingly demonstrate that blade vibration response does not increase consistently with turbine load. Instead, a non-monotonic correlation is observed between vibration response and turbine load. The energy analysis is employed to understand the phenomenon and the results manifest that the variation of energy imposed on blade suction surface is the direct reason for the non-monotonic correlation. Detailed flow field analysis further suggests that the non-monotonic trend of energy on suction surface is caused by the interaction of two flow structures at different turbine loads: separation vortex at blade leading edge and tip leakage vortex caused by pressure difference between pressure surface/suction surface. The study of blade excitation in this research can enlighten the new design of vaneless turbine with both good performance and high reliability.

Spectral proper orthogonal decomposition of compressor tip leakage flow

To identify the spatiotemporal coherent structure of compressor tip leakage flow, spectral proper orthogonal decomposition (SPOD) is performed on the near-tip flow field and the blade surface pressure of a low-speed compressor rotor. The data used for the SPOD analysis are obtained by delayed-detached eddy simulation, which is validated against the experimental data. The investigated rotor near-tip flow field is governed by two tip leakage vortices (TLV), and the near-tip compressor passage can be divided into four zones: the formation of main TLV (Zone I), the main TLV breakdown (Zone II), the formation of tip blockage cell (Zone III), and the formation of secondary TLV (Zone IV). Modal analysis from SPOD shows that a major part of total disturbance energy comes from the main TLV oscillating mode in Zone I and the main TLV vortex shedding mode in Zone III, both of which are low-frequency and low-rank; on the contrary, modal components in Zones II and IV are broadband and non-low-rank. Unsteady blade forces are mainly generated by the impingement of the main TLV on the blade pressure surface in Zone III, rather than the detachment of the secondary TLV from the blade suction surface in Zone IV. These identified coherent structures provide valuable knowledge for the aerodynamic/aeroelastic effects, turbulence modeling, and reduced-order modeling of compressor tip leakage flow.

Optimization of the centrifugal slurry pump through the splitter blades position

Optimal transfer of two-phase solid-liquid flow (slurry flow) has long been a major industrial challenge. Slurry pumps are among the most common types of centrifugal pumps used to deal with this transfer issue. The approach of improving slurry pumps and consequently increasing the efficiency of a flow transmission system requires overcoming the effects of slurry flow such as the reduction in head, efficiency, and wear. This study attempts to investigate the changes in the pump head by modifying the slip factor distribution in the impeller channel. For this purpose, the effect of splitter blades on slip factor distribution to improve the pump head was investigated using numerical simulation tools and validated based on experimental test data. Next, an optimization process was used to determine the characteristics of the splitter (i.e., length, number, and environmental position of the splitter) based on a combination of experimental design methods, surface response, and genetic algorithm. The optimization results indicate that the splitters were in a relative circumferential position of 67.2% to the suction surface of the main blade. Also, the optimal number and length of splitter blades were 6 and 62.8% of the length of the main blades, respectively. Because of adding splitter blades and the reduction in the flow passage, the best efficiency point (BEP) of the slurry pump moved toward lower flow rates. The result of splitter optimization was the increase in pump head from 29.7 m to 31.7 m and the upkeep of efficiency in the initial values.

Unsteady fluidic oscillators for active controlling boundary layer separation in an ultra-high-lift low-pressure turbine

This study used large eddy simulation (LES) to investigate the control mechanism of a fluidic oscillator in the suppression of non-reattachment separation of a boundary layer from an ultra-high-lift, aft-loaded, low-pressure turbine under low Reynolds number. The internal flow characteristics of the fluidic oscillator were examined, with a focus on the influence mechanism of the pulse jet from the fluidic oscillator on boundary layer separation and transition. The effects of different jet angles (θ) on the suppression of separation bubbles were also compared in detail. Finally, the mechanism of interaction between the fluidic oscillator jet and the blade suction surface boundary layer was assessed. It was found that the pulse jet of the fluidic oscillator generated a streamwise vortex pair above the surface of the blade suction, which promoted an exchange of momentum between the boundary layer for the blade suction surface and the main flow, and clearly suppressed boundary layer separation. The streamwise vortex pair at θ=30° showed the characteristics of higher strength, smaller size, slower decay, and longer penetration distance than the results at θ=90°, such that the momentum exchange between the low-energy fluid inside the boundary layer and the main flow is sustainable, which promoted the laminar boundary layer to produce bypass transition and significantly improved the aerodynamic performance of the turbine.

Combined flow control with full-span slot and end-wall boundary layer suction in a large-camber compressor cascade

To investigate combined flow control strategies with full-span slot and end-wall (EW) boundary layer suction, a large-camber compressor cascade was treated with a full-span slot configuration firstly. Then, two combined flow control schemes with different EW boundary layer suction slots were set up based on the full-span slot configuration. Finally, the performance of the baseline cascade and the slotted cascades was evaluated and compared numerically. The results show that the full-span slotted scheme can eliminate the trailing edge (TE) separation near the blade midspan and weakens the corner separation. However, the EW secondary flow still develops on the blade suction surface (SS) before the full-span slot outlet and separates to form the wall vortex (WV). In contrast, the two combined flow control schemes can effectively inhibit the development of the EW secondary flow on the blade SS, contributing to the smaller total pressure loss and stronger static pressure recovery capacity. Between them, the combined flow control scheme with full-chord-length EW suction slot behaves better. It can effectively eliminate the concentrated shedding vortex, WV and corner vortex in the cascade passage, and the passage vortex is also weakened to some extent. Therefore, the TE separation and the corner separation are basically eliminated. The total pressure loss, flow turning angle and static pressure coefficient can be increased by an average of −38.4%, 3.1° and 16.2% in the combined flow control cascade with full-chord-length EW suction slot respectively, which is beneficial for improving the stability margin and static pressure recovery capacity of compressor blades.

The Tip Clearance Cavitation Mechanism of a High-Speed Centrifugal Pump with a Splitter-Bladed Inducer

For a high-speed centrifugal pump, cavitation occurs easily. To equip a high-performance splitter-bladed inducer upstream of the pump is an effective method to suppress cavitation. In this paper, an external characteristics experiment of the high-speed centrifugal pump with a splitter-bladed inducer is carried out, and the corresponding numerical calculations are completed. The research shows that the results of the numerical calculation are credible. Numerical cavitation calculations under eight different tip clearance conditions are carried out. First, it is found that the tip clearance (TC) has a certain impact on the head of the centrifugal pump. When TC is in a small range, the clearance leakage is small, and the impact on the head of the pump is not so obvious, which can give the pump a higher performance. Second, it is found that TC has a certain influence on the static pressure distribution in the cascade passage of the splitter-bladed inducer. When TC is in a certain range, the increasement in TC will aggravate the cavitation at the suction surface of the long blades near the inlet. When it exceeds the certain range, it will cause cavitation at the outlet of the inducer. At last, it is found that the cavitation’s severity and position of the inducer are closely related to TC. TC affects the magnitude and position of vorticity in the inducer’s passage. In this paper the flow mechanism of TC is revealed, and its research results can provide theoretical basis and technical support for the design of the tip clearance of the inducers.

Unsteady pressure measurement and numerical simulations in an end-wall region of a linear blade cascade

This contribution describes experimental and numerical research of an unsteady behaviour of a flow in an end-wall region of a linear nozzle cascade. Effects of compressibility (M_mathrm {2,is}) and inlet flow angle (alpha _1) were investigated. Reynolds number (Re_mathrm {2,is}=8.5times 10^5) was held constant for all tested cases. Unsteady pressure measurement was performed at the blade mid-span in the identical position {mathfrak {s}} to obtain reference data. Surface flow visualizations were performed as well as the steady pressure measurement to support conclusions obtained from the unsteady measurements. Comparison of the surface Mach number distributions obtained from the experiments and from the numerical simulations are presented. Flow visualizations are then compared with calculated limiting streamlines on the blade suction surface. It was shown, that the flow structures in the end-wall region were not affected by the primary flow at the blade mid-span, even when the shock wave formed. This conclusion was made from the experimental, numerical, steady as well as unsteady points of view. Three significant frequencies in the power spectra suggested that there was a periodical interaction between the vortex structures in the end-wall region. Based on the data analyses, anisotropic turbulence was observed in the cascade.

Experimental investigation of tandem rotor under clean and radially distorted inflows

With increasing emphasis on renewable sources of energy, the gas turbine engine faces several challenges in evolving its design, to remain relevant. Compressor is one of the main components, which accounts for one-third of the engine length. Compressor designers have been exploring different ideas to achieve maximum pressure rise with minimum number of stages required. Tandem blading is one such novel design that has demonstrated higher diffusion capability than a single rotor blade. A single blade, with a higher diffusion factor, carries the risk of flow separation against the adverse pressure gradient of the compressor flow. In the tandem blading concept, a single blade is split into forward and aft blade. The gap that is created between the forward and aft blade, serves as a mechanism to energize the sluggish flow over the aft blade suction surface, which in turn helps in mitigating the flow separation. The present experimental work is aimed at exploring the feasibility of a tandem rotor in an axial flow compressor under the clean and radially distorted inflows. Steady and unsteady experimental results of the tandem rotor are included in this paper. The stage performance characteristics, variation of total pressure, flow coefficient, and exit flow angle along the blade span for clean and distorted flow is included in this paper. Some results of a steady Reynolds-averaged Navier-Stokes simulation are also included to give some insight into the complex flow field of the tandem rotor. Wavelet transform, fast Fourier transform analysis, and visual inspection of casing pressure traces are used to analyze the unsteady result of the tandem rotor in clean and distorted flow. The tandem rotor is able to achieve its design pressure ratio and has a stall margin of 9% under the clean flow condition. Initially, stall appears as a low-intensity spike for all the cases, which turns into a long length-scale disturbance within three rotor revolutions. A modal wave of low frequency is also observed under clean and distorted inflows.

Analysis of vortex cooling fluid-structure interaction under different vortex chamber curvature

The vortex cooling with cascade channel and blade leading edge solid region is established. The flow and heat transfer properties of vortex cooling region, and the stress and displacement properties of blade solid region are analyzed by the fluid-structure interaction method. The ellipses edges with vertical axis to horizontal axis ratio a/b of 0.48, 0.72, 1.00, 1.31 and 1.73 are utilized to form the vortex chamber with different curvature. Influences of vortex chamber curvature on the vortex cooling fluid-structure interaction characteristics are researched to reveal the vortex cooling high heat transfer mechanism deeply. Results show that, for a/b decreasing from 1.73 to 0.48, the overall average Nusselt number and comprehensive heat transfer factor will first increase and then decrease, and the drag coefficient will gradually decrease. As a/b decreases, the high Nusselt number region moves from the target wall next to the nozzle to the target wall under the nozzle and at the vortex chamber bottom. With decreasing a/b, the thermal stress and thermal displacement on the blade pressure surface gradually decrease, while on the blade suction surface the thermal stress first decreases and then increases, and the thermal displacement first increases, then decreases and finally increases. In this study, compared with a/b = 1.73, the heat transfer performance for a/b = 0.72 has been enhanced by 21.00% and can provide the best protection for the blade.

Direct numerical simulations of flutter instabilities over a vibrating turbine blade cascade

This paper presents direct numerical simulations (DNS) on unsteady turbulent flow in a vibrating low-pressure turbine blade cascade to predict the flutter instabilities and explores the effects of blade oscillations on the flow structure and flow separation point. The spectral/hp element method is employed for the three-dimensional simulations of the domain. This method enables capturing more details about the flow structure and vortex generations compared to the URANS methods. The method can aid in understanding the physics of these complex fluid–structure interaction problems while it requires much less computational time compared to the other DNS models. The blade vibration frequency is varied from 5.2 Hz to 10.3 Hz with maximum vibration amplitude of 3% of chord length at the blade tip. The results illustrate that the vortex generation becomes stronger over the blades with higher vibration frequencies compared to the stationary ones. The main reason for the additional vortex generation and recirculations over the oscillating blades is the additional flow disturbance due to blade vibration and its interactions with the shear-layer on the turbine blade cascade. It is seen that the vortex shedding is growing around the trailing edge and become stronger on the suction surface of the vibrating blade. The flow separation over the suction surface of the stationary blade occurs at Ssep∕S0=0.391, while it occurs at 0.372 over the oscillating blade with f=5.2Hz.

Совершенствование швартовных испытаний главного двигателя, работающего на винт фиксированного шага

The most important stage in vessel’s construction is acceptance tests. By testing the main power plant of the vessel the design solutions adopted to ensure stable operation of the main engine and the propeller are checked. Such a check of the main engine according to design characteristics at the quay wall can significantly reduce sea trials cost. In practice, the peculiarities of the propeller operation at zero free-flow velocity at the quay wall limit the operating modes of the main power plant and the possibilities of mooring tests. There are considered the traditional and innovative simulation methods and tools used in mooring tests. The methods allow unloading the engine in terms of torque bringing its operation mode closer to the design parameters. An urgent scientific and technical problem has been solved to reduce the mechanical stress of the main engine, which operates according to the mooring characteristic on a fixed pitch propeller. The factors influencing the value of the resistance moment of the propeller at a zero vector of the incident flow are determined. Possible directions for improving the acceptance tests of the main power plant by supplying an additional environment, i.e. air to the suction surface of the propeller blade, are substantiated. In the complex of computational fluid dynamics, a computational model of a fixed pitch propeller has been created. The amount of air required to change the propeller operating mode has been estimated. Resistance moment of the propeller for various methods of air supply to the propeller has been analyzed. Additional means of controlling the main engine operating mode at the stages of the ship's life cycle are proposed.

Performance enhancing for a highly loaded tandem cascade by endwall incoming vortex–corner separation interaction

In highly loaded tandem compressor cascades, corner separations can still exist. In order to eliminate corner separations in highly loaded tandem compressor cascades, incoming vortex–corner separation interaction mechanism was investigated. Different schemes of the vortex generators, which located at different pitchwise locations and could generate vortexes with different rotation directions, were designed and investigated numerically. Results show that, severe corner separation occurred at the front blade passage of the tandem cascade; by utilizing flow control method of incoming vortex–corner separation interaction, the corner separation could be reduced significantly. The optimal control effect of incoming vortex on corner separation was achieved with anticlockwise rotation and the vortex generator is located right ahead of the leading edge of tandem cascade, a maximum loss coefficient reduction of 21.8% being achieved. Different from single blade configuration, the boundary layer of tandem cascade was regenerated at rear blade suction surface due to the injection flow from blade gap between the two blades. Though corner separations could be reduced at both conditions, the loss of tandem cascade with clockwise incoming vortex is higher than that with anticlockwise vortex, and a smaller corner separation region at suction surface was achieved by utilizing clockwise vortex. The mechanism was that anticlockwise incoming vortex reduced the corner separation but increased secondary flow, while clockwise vortex enhanced passage vortex and decreased secondary flow. For clockwise incoming vortex near pressure surface, the vortex would be divided into two parts at the leading edge of rear blade, one would go through the blade gap and deteriorate flow fluid near rear blade suction surface, the other flowed downstream along pressure surface. The rotation direction of different incoming vortexes became the same as the passage vortex at rear blade passage of tandem cascade, which was mainly due to the effect of secondary flow.

Unsteady characteristics of pressure on wind turbine blade surface in the field

Field experiments are carried out to investigate the fluctuation characteristics of pressure on wind turbine blade surface in real operating environments. The tested wind turbine positioned pressure tapes along the blade span to obtain the dynamic pressure of seven airfoil sections over six rotation periods, and analyzed its time-domain, frequency domain, and standard deviation. The results show that the pressure on blade surface presents highly unsteady characteristics, and rotation of the wind turbine is one of the main factors that causes pressure fluctuations on the blade surface. The standard deviation of pressure near the leading edge of each airfoil section is relatively larger, indicating that the leading edge is the most sensitive to field wind conditions. Compared with the pressure surface, the blade suction surface contributes more to wind turbine power fluctuation and is more sensitive to various unsteady sources. Moreover, the standard deviation of the pressure on the blade pressure surface is largest at the tip, and the standard deviation of the pressure on the blade suction surface is clearly divided into two regions along the chord direction with different scales at different spanwise sections.

Effect of particle mass concentration on erosion characteristics of self-priming pump

The self-priming pump is widely used in conveying the solid-liquid two-phase flow medium. The particles in the medium erode the components, leading to structural damage and failure. The computational fluid dynamics (CFD) model of the 65ZW30-20 self-priming pump is built to study erosion characteristics and mechanisms. FLUENT, along with the Discrete Phase Model and Oka erosion model, is applied for the numerical simulation. The particle distribution, impact times and velocity, and trajectories are taken into consideration to investigate the erosion characteristics in each component. The results show that with the increase of the particle concentration, the head and efficiency decreases gradually. The volute wall and blade leading edge are the most vulnerable regions to erosion, because of a large number of impact times and high impact velocity. Also, the particles impact the front gap wall for fewer times and the hub with lower velocity, which leads to a slighter erosion. Besides, the particle trajectories indicate that some particles impact the blade suction surface and the paraxial area of the shroud, rendering considerable erosion.