Blade Surface Research Articles

WAKE – SEPARATION BUBBLE INTERACTION OVER AN EXPERIMENTALLY SIMULATED AXIAL COMPRESSOR BLADE UNDER LOW REYNOLDS NUMBER FLOW

Abstract For the most part, the flow over an axial compressor blade is subjected to adverse pressure gradients. Under low Reynolds number conditions, the flow could separate off the blade surface especially on the suction side, where it first accelerates to a peak velocity and then decelerates towards the blade exit. The ‘separation bubble’ thus formed could trigger laminar to turbulent flow transition on reattachment downstream of the point of separation. Since blade profile losses depend on the transition location, the modification of the separation bubble due to any upstream generated disturbances is of great interest. In this paper the interaction between periodically incoming wakes and the separation bubble that exists on the blade surface is investigated. Results are presented from wind tunnel experiments conducted over a flat plate that is imposed with a surface pressure profile similar to that over a highly loaded compressor blade. The wakes are introduced using a bar passing mechanism that produces representative unsteady parameters. The spatio-temporal development of the flow along the mid-span region is described with the help of particle-image-velocimetry based flow mapping at a relatively low Reynolds number of 210,000. Several interesting observations were made, but the most important one is the existence of a slow-moving thickened boundary layer feature that convects immediately behind the wake. While the calmed region that forms behind this feature can suppress the bubble, the thickened boundary layer itself is seen to have high unsteadiness and contributes to a large momentum deficit.

ANALYSIS OF THE INSTANTANEOUS FILM COOLING EFFECTIVENESS ON SHOWERHEAD FILM COOLING USING FAST RESPONSE PRESSURE SENSITIVE PAINT (FAST-PSP)

Abstract The instantaneous effect of unsteady wakes on film cooling effectiveness using a fast response pressure sensitive paint (PSP) was studied. Testing was performed in a five passage, low speed wind tunnel using scaled versions of typical high-pressure blades (axial chord of 17 cm). The blowing ratios studied include 0.8 and 1.2, with a density ratio of 1.0 and 1.5 at each blowing ratio. Unsteady wakes were produced by a spoked wheel wake generator. The wake generator, utilizing a varying number of rods and rotational speeds, produced Strouhal numbers of 0.1 and 0.3 while the wind tunnel inlet mainstream Reynolds number remained constant at 300,000 (mainstream velocity of 21 m/s) for every test case. For each Strouhal number, blowing ratio and density ratio studied, several positions within the period between rods were recorded. Results show that the location of the wake along a blade's surface had a significant impact on the film cooling effectiveness in the immediate location of the wake. An overall fluctuation of up to 69% in film cooling effectiveness was observed within the wake period. Conclusions also show that while mainstream flows with higher Strouhal numbers tend to decrease film cooling effectiveness, the fluctuation of film cooling effectiveness at higher Strouhal numbers was reduced when compared to results utilizing lower Strouhal numbers. A comparison of results from tests at different density ratios showed a much smaller change in the instantaneous film cooling effectiveness between test cases.

Aviation-engine blade surface anomaly detection based on the deformable neural network

Aviation-engine blade surface anomaly detection based on the deformable neural network

Effects of variable blowouts on aerodynamic loss reduction performance of compressor bionic blades

Abstract A passive flow control method, inspired by blowouts, is employed to eliminate flow separation and reduced losses associated with higher compressor loads. By implementing bionic-blowout variant dimples on the blade suction surface, the flow characteristics of the dimple-shaped cascade were investigated. The loss generation mechanism was also analysed. Firstly, the reliability of the numerical method was confirmed through experimental validation. Subsequently, biomimetic principles were applied to arrange dimples on the suction surface of the cascade blades, and the effects of various blowouts were analysed The result revealed that vortices within the dimples induce external fluid into the dimples, enhancing the turbulent kinetic energy of the external fluid and improving wall-adjacent flow adherence. The bionic-blowout variant dimples creates a "rolling bearing" effect that reduces frictional losses, which control flow separation. Within a certain blowout range, the bionic-blowout variant dimples significantly improve the flow conditions. At -6° angle of attack, the total pressure loss of the dimple-structured cascade decreased by 35.85%, and the pressure ratio increased by 2.35%. The bionic-blowout variant dimples on the blade suction surface exhibit a three-dimensional disturbance effect. The induced vortex structures regulates the boundary layer transition and suppress the formation of laminar separation bubbles, effectively improving the flow conditions near the corner region.

The effect of blade surface grooves on performance of axial fan

This paper explores the effect of blade surface grooves on the axial fan of central air-conditioner outdoor units in detail through experiments and three-dimensional unsteady simulations. The experimental results reveal that the newly designed fan with surface grooves can reduce noise by 1.2 dB(A) without sacrifice of aerodynamic performance. The simulation results demonstrate that the effect of the surface grooves is localized and does not alter the overall load distribution of the axial fan. However, it does affect the tip leakage vortex. The tip leakage vortex is a large-scale vortex that interacts with small-scale vortices shedding from the blade surface grooves, resulting in the weakening of the tip leakage vortex and the secondary tip leakage vortex. Ultimately, this leads to a reduction in the noise of the air-conditioner outdoor unit. This new strategy based on blade surface geometric design provides a novel idea for tip leakage flow control and has significant engineering application value.

On unsteady flow characteristics in a water-jet pump based on proper orthogonal decomposition method under different inflow conditions

Considering the complex flow characteristics of the water-jet pump and the anisotropy of Reynolds stresses, a hybrid Reynolds-averaged Navier–Stokes/large-eddy simulation method based on von Kármán scale and nonlinear correction has been developed, while its effectiveness has also been verified. The proper orthogonal decomposition method is employed to study the unsteady flow characteristics inside a water-jet pump due to its advantages in flow field analysis. The internal and external characteristics of the water-jet pump under two kinds of inflow conditions are comparatively analyzed, and the intrinsic influence mechanism of nonuniform inflow on the performance of the water-jet pump is investigated. The results indicate that nonuniform inflow causes the overall decrease in the pump head curve, and occurs serious reverse flow at impeller outlet near blade tip region, which in turn generates a large energy dissipation. The flow state is relatively smooth under uniform inflow condition, while the nonuniform inflow makes tip leakage flow induce many unstable flow structures, causing large turbulent kinetic energy and low pressure difference between the pressure surfaces and suction surfaces of impeller blades. There are multiscale flow structures in the water-jet pump, with large scales corresponding to low-order modes, which play a dominant role in turbulent movement and can be used as an important element for evaluating hydraulic performance. The energy content of low-modes is lower and the distribution of flow structures in each-order mode is more chaotic in the water-jet pump for nonuniform inflow compared to the ones for uniform inflow.

Effect of tip injection on performance of highly loaded helium compressor in high-temperature gas-cooled reactor

As one of the representatives of the fourth-generation advanced nuclear reactor, the continuous development and application of high-temperature gas-cooled reactor (HTGR) technology has promoted the technical progress of the whole nuclear energy field. Helium compressor is one of the core components of HTGR. The highly loaded helium compressor effectively solves the disadvantages of the low single-stage pressure ratio and numerous stages of the traditional helium compressor. But it also brings a more complex tip-leakage flow. Tip injection, which is an active control method, can effectively control the tip clearance leakage and inhibit the development of the leakage vortex. This paper analyses the effects of axial deflection angle and injection pitch angle on the rotor performance of a highly loaded helium compressor via numerical simulation and validates them via experiment. Results show that the leakage vortex can be blown to the pressure surface of the adjacent blade by proper axial deflection angle to reduce the vorticity of the leakage vortex. The injection pitch angle directly affects the intensity of the leakage vortex during its initiation and development. When the axial deflection angle is 60° and the injection pitch angle is 20°, the adiabatic compression efficiency and total pressure ratio increase by 0.554 % and 0.160 % respectively under the design condition, and by 0.822 % and 0.162 % respectively under near-stall conditions.

Effects of surface curvature on rain erosion of wind turbine blades under high-velocity impact

Rain erosion induced by raindrops impacting wind turbine blades at high velocity can change the aerodynamic characteristics of the blades and increase maintenance costs. Previous numerical studies on rain erosion have not considered the curvature of the blade leading-edge surfaces and assumed them to be flat surfaces. This study established a fluid-solid coupled numerical model combining the finite element method and smooth particle hydrodynamics. It models a water droplet with a diameter of 2.74 mm impacting the curved leading-edge surface of wind turbine blades with radii of curvature of 1.35 mm, 6.75 mm, 67.5 mm, and infinite at 110 m/s, and the effects of the radius of curvature on the impact response were analyzed. The results show that as the radius of curvature of the leading-edge surface increases, the surface obstructs the water droplet more significantly, and the lateral jetting of the water droplet is enhanced. A larger radius of curvature causes more droplet impact energy to be transferred to the curved surface, increasing the contact force between the water droplet and the surface. The increased transferred impact energy results in higher stress and plastic strain values. The decrease in the radius of curvature of a curved surface increases the error in the stress and strain results obtained by assuming it to be a flat surface.

Investigation on the integrated characteristics of n-decane/air rotating detonation combustor and supersonic turbine

In this study, the two-dimensional numerical simulations are conducted to study the flow field characteristics, turbine performance and loss mechanism of integrated system of rotating detonation combustor and supersonic turbine under two different directions of detonation wave propagation. The results indicate that the propagation direction of RDW affects the incident angle between OSW and guide vanes, resulting in different operating modes for aligned and unaligned modes. OSW in the turbine cascade undergoes the leading-edge shock, blade surface reflection and trailing edge diffraction. The backward-propagating rake-type shock envelope is formed due to leading-edge shock of the rotor. In misaligned mode, the stator has higher damping of both pressure and temperature. The stator significantly improves the circumferential uniformity of both velocity and pressure, particularly when operating in aligned mode. The total pressure loss in aligned mode is less, therefore the turbine achieves higher rim work and efficiency. The viscosity is one of the main sources of loss in the flow field. The reflected shock waves at the leading edge of the rotor and in the stator cascade are the primary factors contributing to the leading-edge vortices on the stator vanes.

Analysis of camber ratio variation on B-Series propeller performance by using combined panel-vortex method and blade-element theory

Abstract The camber ratio of a propeller significantly affects its hydrodynamic performance. The camber ratio particularly affects the lift force generated by the propeller blades, which ultimately affects the propeller thrust and torque. In this study, effects of camber ratio variations are investigated by using a combined method of panel vortex method and blade element theory. The camber ratios considered in this study are as follows: 0% (0.00, original foil), 1.6% (0.016), 2.2% (0.022), and 2.8% (0.028). A larger camber ratio results in a more convex propeller blade surface. Calculation results show that the larger the camber ratio, the higher the thrust and torque coefficients. The camber ratio of 2.2% (0.022) gives the highest propeller efficiency of 58.5% at the advance coefficient J = 0.7.

A Review on Corrosion Behavior and Surface Modification Technology of Nickel Aluminum Bronze Alloys: Current Research and Prospects

Nickel aluminum bronze alloy, a complex alloy containing multiple phases, has become the most common material for naval propellers due to its good corrosion resistance. Traditional cast nickel aluminum bronze shows serious corrosion behavior in harsh service environments. This article reviews progress on the corrosion behaviors and corrosion mechanism of nickel aluminum bronze in highly corrosive and complex marine environments and systematically discusses the research status of the surface modification technologies such as laser surface strengthening, mechanical shot peening, friction stir and thermal spraying, and so on. To improve the comprehensive performance of nickel aluminum bronze, this work focuses on analyzing the effect of process parameters on the corrosion resistance of nickel aluminum bronze alloy while researching propeller blade surface modification technology. Finally, the future research and development direction of nickel aluminum bronze in the fields of laser and arc additive manufacturing is prospected.

Research on unsteady flow characteristics of turbocharger turbine stage with coupling inlet and exhaust casings

The inlet and exhaust casings of marine turbochargers are closely coupled to the axial flow turbine. These are crucial parts that work with the axial flow turbine and have the ability to raise the power plant’s output power even higher. Their final stage of the axial flow turbine and the exhaust casing’s complex flow due to their close relationship will have a significant effect on each other’s aerodynamic performance. However, most existing studies have not paid sufficient attention to this coupled transient interaction. In this paper, the flow interaction between the axial flow turbine and the inlet and exhaust casings is studied. Particular attention is paid to the study of the coupled flow characteristics under design and variable operating conditions. This study is carried out using coupled computational fluid dynamics (CFD) simulation. The computational domain consists of an inlet casing, 28 stator blades, 43 rotor blades, and an exhaust casing. The commercial CFD software ANSYS CFX solver and the SST turbulence model are used to simulate the unsteady flow field of the turbocharger axial turbine coupled to the inlet and exhaust casings. In this paper, the turbine flow field and the inlet and exhaust casings flow fields are analyzed, and the influence of the exhaust casing on rotor surface pressure fluctuation is discussed. In addition, the flow field distribution and performance parameters of the axial flow turbine coupled with the inlet and exhaust casings under three different operating conditions have been calculated and analyzed. The results show that the inlet casing affects the circumferential distribution of the stator leading edge pressure, while the asymmetric back pressure caused by the exhaust casing flow field causes the low-frequency pressure fluctuation at the rotor blade surface. At the trailing edge of the suction surface, the complex flow separation and vortex structure in the exhaust casing are the main factors causing rotor-stator interaction. The low-frequency fluctuation amplitude caused by the exhaust casing is greater than that caused by the high-frequency fluctuation of the rotor-stator interaction. Moreover, as the flow coefficient increases, the low-frequency fluctuation amplitude is much greater than the high-frequency fluctuation amplitude.

Cooled MarkII blade surface pressure and temperature distribution by a conjugate heat transfer analysis using Reynolds stress baseline turbulence model

Cooled MarkII blade surface pressure and temperature distribution by a conjugate heat transfer analysis using Reynolds stress baseline turbulence model

Flow disturbance by intrusive instrumentation located on the surface of a compressor blade

In this paper, we present an experimental and numerical investigation into the flow disturbance by intrusive instrumentation in the form of spanwise pressure tubes mounted on the pressure and suction side of a compressor blade in a linear cascade wind tunnel at a moderate subsonic Mach number of 0.5 and a Reynolds number of 790,000. The pressure tubes were modelled as simplified bumps extending over the entire span with a width of 24% of the chord length and a height of 67% of the maximum blade thickness. The leading edge of the bumps is located at 30% of the streamwise surface length. We found that the total pressure losses generated by these pressure tubes are considerably larger when they are placed on the suction side of the blade. The suction-sided bump increases the total pressure loss coefficient by a factor of four, while the pressure-sided bump approximately doubles it. CFD simulations reveal that the suction-sided bump causes the flow to form a large, open recirculation zone, while for the pressure-sided bump, the flow reattaches near the trailing edge. In conclusion, we provide insights into the effects of pressure tubes on the losses generated by compressor blades. The mounted tubes significantly impact the flow and should be carefully considered during instrumentation design.

Assessing the Effect of Uneven Inlet Velocity on the 24 ft Diameter MinwaterCSP Fan Using a Unique Pressure Sensing System

An industrial-grade pressure sensing system was designed for installation on the surface of the 24 ft (7.315 m) diameter M-fan that is installed on the MinwaterCSP test facility. The facility has significant cross draft effects due to the proximity of a canal that runs underneath the centre of the facility. This canal causes disturbance of the inlet air flow distribution. Due to the constant rapid change in air velocity and direction with blade rotation, the pressure on the blade fluctuates. The velocity distribution was measured experimentally using the installed anemometers. The uneven inlet velocity distribution led to fluctuations in blade surface pressures, which were measured using the uniquely designed pressure sensing system. The measured results were compared to the results of a Computational Fluid Dynamics (CFD) model of the MinwaterCSP test facility. The CFD simulations consisted of two parts. Firstly a 3-dimensional representation of the facility, which was used to get the velocity distribution data and secondly a 2-dimensional airfoil simulation which was used to obtain the surface pressure distribution on the blade surface. The 3-dimensional CFD model made use of an actuator disk model to represent the effect of the fan. The experimental results showed a higher velocity and relative surface pressure distribution at locations correlating to the location of the canal. The simulation was able to replicate these distribution fluctuations. The results of the experimentally measured fan blade surface pressure at the fan suction side correlated within 9% to those of the simulation results.

Brief communication: Real-time estimation of the optimal tip-speed ratio for controlling wind turbines with degraded blades

Abstract. Rotor performance is adversely affected by the wear and tear of blade surfaces caused, for example, by rain, snow, icing, dirt, bugs and aging. Blade surface degradation changes the aerodynamic properties of the rotor, which in turn changes the optimal tip-speed ratio (TSR) and the corresponding maximum power coefficient. Below the rated wind speed, if a turbine continues to operate at the manufacturer-designed optimal TSR, the rotor power could decrease more than necessary unless the optimal TSR is corrected to compensate for blade degradation or blade surfaces are restored. Re-tuning the tip-speed ratio can lead to an improvement in energy capture without blade repairs. In this work, we describe a real-time algorithm to re-tune the tip-speed ratio to its optimal but unknown value under blade degradation. The algorithm uses power measurements only and the Log-Power Proportional-Integral Extremum Seeking Control (LP-PIESC) strategy to re-tune the TSR. The algorithm is demonstrated in simulations to command the set-point TSR required by a generator speed control loop that maximizes power at below-rated wind speeds. Comparison of this solution with a baseline controller that uses the optimal TSR for a rotor with clean blades demonstrates improvements in energy capture between 0.5 % and 3.4 %, depending on the severity of blade degradation and the wind conditions. These results are obtained using the OpenFAST simulation tool, the National Renewable Energy Laboratory (NREL) 5 MW reference turbine and the NREL-developed Reference Open-Source Controller (ROSCO).

Microscopic analysis of Valeriana stolonifera and Valeriana collina leaves

Plants of the Valeriana species are distributed in various parts of the world, especially in Europe and Asia. A high content of polyphenolic compounds, including flavonoids and hydroxycinnamic acids with expressed biological activity, was previously identified within the herb of the studied Valeriana species. Morphological and anatomical data can be used in phylogenetics of species and genera to find out diagnostic and age-related characteristics of plants. This led us to microscopic studies of aerial organs of the above-mentioned Valeriana species. The aim of the work is to conduct a comparative study of the diagnostic features within the morphological and anatomical structure of Valeriana stolonifera and Valeriana collina leaves. Materials and methods. Both raw and dried plant material of V. stolonifera and V. collina was used for microscopic studies. Temporary micropreparations were made using generally accepted methods. The anatomical features of the raw material were examined using Carl ZEISS “AxioStar Plus” and “Primo Star”. Results. The study identified key morphological and anatomical features of the species, which should be considered for the identification and standardization of promising medicinal plant materials and within the development of methods of analytical and regulatory documentation. Conclusions. The key microscopic differences in the leaves of the studied species lie in the structure of the adaxial and abaxial surfaces of the leaf blade. The upper epidermis consists of large elongate cells with wavy walls. The cells of the lower epidermis are smaller and have more sinuous walls compared to the upper epidermis cells. The degree of wall sinuosity varies between species – V. collina is characterized by more sinuous cells in both the upper and lower epidermis compared to V. stolonifera. The absence of stomata on the upper epidermis is a common feature for both species.

Adaptive Sampling Technique for Free-Form Surface of Aero-Engine Blades Based on Discrete Curvature

Adaptive Sampling Technique for Free-Form Surface of Aero-Engine Blades Based on Discrete Curvature

Infrared Thermography of Turbulence Patterns of Operational Wind Turbine Rotor Blades Supported With High‐Resolution Photography: KI‐VISIR Dataset

ABSTRACTWith increasing wind energy capacity and installation of wind turbines, new inspection techniques are being explored to examine wind turbine rotor blades, especially during operation. A common result of surface damage phenomena (such as leading edge erosion) is the premature transition of laminar to turbulent flow on the surface of rotor blades. In the KI‐VISIR (Künstliche Intelligenz Visuell und Infrarot Thermografie—Artificial Intelligence‐Visual and Infrared Thermography) project, infrared thermography is used as an inspection tool to capture so‐called thermal turbulence patterns (TTPs) that result from such surface contamination or damage. To complement the thermographic inspections, high‐resolution photography is performed to visualise, in detail, the sites where these turbulence patterns initiate. A convolutional neural network (CNN) was developed and used to detect and localise turbulence patterns. A unique dataset combining the thermograms and visual images of operational wind turbine rotor blades has been provided, along with the simplified annotations for the turbulence patterns. Additional tools are available to allow users to use the data requiring only basic Python programming skills.

Numerical research on hydrodynamic performance of toroidal propeller under the influence of geometric parameters

Recent advancements in high-efficiency, low-noise toroidal propellers have garnered significant interest due to their potential to revolutionize maritime propulsion. This study addresses this gap by leveraging established geometrical modeling methods for toroidal propellers to design a novel variant, and assesses its hydrodynamic performance using the Reynolds-averaged Navier-Stokes (RANS) method coupled with the Shear Stress Transport (SST) k-ω turbulence model. First, the paper introduces the toroidal propeller concept and modeling method before analyzing the impact of grid size on numerical simulations. The correspondence between numerical results and experimental data is then established to validate the computational model's accuracy. Following this, the study explores the hydrodynamic performance of the toroidal propeller, including pressure distribution on the blade surface and the flow field dynamics in the propeller's wake across varying advance coefficients. Subsequently, it examines the influence of geometric parameters such as axis span ratios, lateral angles, roll angles, and vertical angles, on the hydrodynamic performance, elucidating their effects on the pressure distribution profiles at radial sections, thrust coefficient, and open water efficiency. The findings provide substantial guidance for the geometric parameter selection in the optimal design of future toroidal propellers.