Leading Edge Profile Research Articles

Performance improvement of multi-blade centrifugal fan based on impeller outlet flow control

The impeller of the multi-blade centrifugal fan significantly impacts the fan's internal flow field and aerodynamic performance. To improve the axial flow distribution along the impeller and suppress the blade passage backflow at the impeller outlet of multi-blade centrifugal fans, a method of variable chord length blade design is proposed. Simultaneously, optimization models are established with static pressure and efficiency as objectives. By altering the control points of the Bezier curve, the leading-edge profile of the impeller is optimized. The results indicate that using variable chord length blades can expand the operating range of the multi-blade centrifugal fan. The maximum flow rate improvement reaches 10.6%. Significant enhancements in the aerodynamic efficiency of the multi-blade centrifugal fan are observed at low flow rates, with a maximum improvement of 4.9%. The variable chord length blade design method enables adjustment of the axial flow distribution at the impeller outlet to better match the impeller's flow requirements. This leads to increased outlet flow on both the shroud and hub sides of the impeller, consequently reducing the backflow area on both sides and improving the blade passage backflow phenomenon. Moreover, variable chord length blades facilitate a more uniform circumferential flow distribution at the impeller outlet, reducing the diversion pressure of the volute tongue, mitigating flow separation within the blade passage, weakening the interaction between the impeller and the volute tongue, and lowering energy losses in the impeller–volute tongue regions. Consequently, this enhances the aerodynamic performance of multi-blade centrifugal fans.

Performance improvement and noise reduction analysis of multi-blade centrifugal fan imitating long-eared owl wing surface

This research was inspired by the long-eared owl's ability to fly silently. For the first time in this study, a wind turbine blade is designed to mimic the wing surface and the leading edge of the long-eared owl. The commonly used two-dimensional blade profile in previous studies is replaced by a more effective three-dimensional profile. This change leads to improved aerodynamic performance of the multi-blade centrifugal fan and reduced noise levels. The airfoil and leading edge profile parameters of the long-eared owl were extracted and utilized. These parameters were used to develop a fitting formula based on their correlation. This formula facilitated the design and optimization of a bionic blade (B-Blade). The results indicate a 4.1% enhancement in the maximum flow rate compared to the original blade fan, alongside a noise reduction of 1.3 dB(A) under identical static pressure conditions. An examination of the internal flow, noise, and sound source characteristics of both fan types was conducted, elucidating the aerodynamic noise mechanism. Fan noise propagation showed pronounced dipole sound source traits. The sound source area at the B-Blade fan's inlet and the volute tongue was more compact, leading to a decrease in mid-low frequency discrete noise. The sound source intensity was also diminished. The B-Blade fan also ameliorated the flow distribution at the impeller outlet, reducing the unstable interaction between the impeller and volute tongue, thereby effectively diminishing noise.

Aerodynamic evaluation of cascade flow with actual geometric uncertainties using an adaptive sparse arbitrary polynomial chaos expansion

In this paper, an adaptive sparse arbitrary polynomial chaos expansion (PCE) is first proposed to quantify the performance impact of realistic multi-dimensional manufacturing uncertainties. The Stieltjes algorithm is employed to generate the PCE basis functions concerning geometric variations with arbitrary distributions. The basis-adaptive Bayesian compressive sensing algorithm is introduced to retain a small number of significant PCE basis functions, requiring fewer model training samples while preserving fitting accuracy. Second, several benchmark tests are used to verify the computational efficiency and accuracy of the proposed method. Eventually, the coexistence effects of six typical machining deviations on the aerodynamic performance and flow fields of a controlled diffusion compressor cascade are investigated. The probability distributions of the machining deviations are approximated by limited measurement data using kernel density estimation. By uncertainty quantification, it can be learned that the mean performance seriously deteriorates with increasing incidences, while the performance at negative incidences is more dispersed. By global sensitivity analysis, the leading-edge profile error should be given high priority when working at negative incidences, and the inlet metal angle error would be carefully inspected first when the cascade works at high positive incidences. Furthermore, controlling the manufacturing accuracy of the suction surface profile error can play a certain role in improving the robustness of aerodynamic performance in off-design conditions. Through flow field analysis, it further proves that actual leading-edge errors are the most important ones to aerodynamics and reveals how the effects of leading-edge errors propagate in the cascade passage, thus affecting the aerodynamic loss.

On the acoustic emission characteristics of airfoils with different trailing edge configurations

The present study experimentally and numerically investigates the flow past flat plates and NACA0012 airfoils with the different trailing edge (i.e., blunt, sharp, and rounded) and both end-rounded configurations on the far-field acoustic emissions and complex flow phenomena to determine the best edge geometry for low noise. The studies are conducted for various jet speeds of 20, 30, and 40 m/s (chordwise Reynolds numbers of 1.812 × 105, 2.72 ×105, and 3.62 ×105). It is observed that all the edge-modified flat plates show the highest directivity at an emission angle of 60° for all jet velocities studied. The comparison of power directivities between realistic and flat plate airfoils reveals that the realistic airfoils radiate lower acoustic emissions as compared to flat plate airfoils, albeit they show a common feature of downstream directivity. In general, the far-field acoustic emissions of both end-rounded plates are observed to be lower as compared to blunt, sharp, and rounded trailing edge geometries. The leading edge modification is also observed to reduce airfoil self-noise. The likely reason for the lower far-field acoustic emissions provided by both end-rounded trailing edged foils is due to the modification in the boundary layer characteristics owing to the presence of smooth flow around the rounded leading edge as well as reduced vortex strength as compared to the other foil geometries. Thus, the present study demonstrates that passive modifications of leading edge profiles are essential along with trailing edge for achieving lower acoustic emissions and higher noise reductions.

Multifunctional Carbon-Basalt hybrid composites against bird strike

A bird strike is a common occurrence during an aircraft's takeoff and landing and is classified as a high-velocity impact, which can cause severe damage, a decrease in aerodynamic efficiency, and may lead to catastrophic failure. High strength composite materials are used in the wing structure to resist the bird strike. Stealth is an important factor for military aircraft, as it reduces the detectability range of the target. The current aircraft wing structure incorporates different systems to perform various functions, so a composite wing capable of performing multiple functions of providing stealth while retaining its existing properties is required. The need for sustainable green materials has shifted the focus to natural materials, and hybridization is the way to improve the properties. The current study proposes a multifunctional hybrid carbon-basalt-polyaniline composite for aircraft wing skin that can absorb electromagnetic (EM) waves while maintaining its mechanical properties. A polyaniline with 5 % weight was found to be optimal, as the prepared sample has a dielectric loss tangent of 2.1396. The hybrid composite was simulated against a bird strike and a maximum deflection of −48.54 mm was observed for a thickness of 1.2 mm. The deflection behavior of the prepared composite was compared to several works, and a thickness of 3.6 mm was found to be optimal for a deflection of −28.97 mm. For a curved leading-edge profile, the observed deflection for 1.488 mm thickness was 580 mm. An all-composite wing model was designed and proposed having two ribs, one spar, and two stringers all modelled in carbon-basalt-PANI composite showing the maximum center point deflection of 450 mm. The prepared multifunctional hybrid composite has a high potential for use in aircraft wing skins due to its reasonable mechanical properties, good EM wave absorption, and ability to withstand bird strike.

Effects of leading edge profiles on flow behavior and performance of supercritical CO2 centrifugal compressor

The supercritical carbon dioxide (sCO2) Brayton cycle is considered one of the promising power cycles. Centrifugal compressors are the core equipment of sCO2 systems. The inlet condition of compressors is near the critical point of CO2, which makes the flow in compressors become more complex and has the risk of condensation. To improve the flow behavior at the leading edge (LE) of the blade, a method of correcting the LE profiles (long-short axis ratio) of the blade was proposed. The cause of condensation at the LE of the blade is analyzed by numerical simulation and the effects of the LE profiles on the flow behavior in the impeller passage and the performance of the compressor. The results show that the suction peak on the LE suction side is changed under different working conditions. With the increase of the long-short axis ratio of the LE of blades, the suction peak at the LE is weakened. Under the design condition, the volume of the two-phase flow in the impeller passage with elliptical LE is 20% lower than that with arc LE. When the long-short axis ratio of the LE is 3∼6, the volume of the low-dryness flow decreases with the increase of the long-short axis ratio under the condition of the small flow rate. Under the design condition, the isentropic efficiency of the compressor with the largest long-short axis ratio of the LE increases by 1.411%, and the pressure ratio increases by 0.0353.

Numerical Investigation of Ice Formation on a Wing with Leading-Edge Tubercles

This work numerically investigates the influence of sinusoidal leading-edge characteristics, often described as wavy leading-edge wings or wings with tubercles, on aircraft icing. Initially, the flow prediction of clean wavy wings is compared to experimental data for model validation. A series of test cases based on the experimental geometry is subsequently established with varying wave amplitudes and lengths. The icing assessment is conducted numerically using the three-dimensional PoliMIce ice accretion toolkit. Firstly, the influence of the three-dimensional flow behavior on the collection efficiency is evaluated. The simulations demonstrate that wavy leading edges with shorter wave lengths and higher wave amplitudes increase the localized impingement of super-cooled water droplets during impact. Secondly, the influence of the wavy leading-edge profile on the ice shapes is assessed for both the rime and glaze ice regime. The results show that the maximum ice thickness is in the vicinity of the wave peaks and troughs; meanwhile, the midsections of the waves have significantly lower levels of ice accretion. The future perspective of this work is to assess the potential for improving the efficiency of anti-icing and de-icing systems using wavy leading edges.

Anti-cavitation leading-edge profile design of centrifugal pump impeller blade based on genetic algorithm and decision tree

Anti-cavitation leading-edge profile design of centrifugal pump impeller blade based on genetic algorithm and decision tree

Numerical investigation of aerodynamic performance of leading edge tubercle airfoil at low Reynolds number

Numerical investigation was made to study the aerodynamic characteristics of the Tubercle NACA2412 airfoil is used in the design of aircraft wing and wind turbine blades. In this paper, computational study aimed to observe the aerodynamic characteristics of 3D airfoil NACA 2412 with peak and trough chord length as 100 mm and 80 mm respectively. The co-efficient of pressure performance of NACA2412 airfoil with tubercle leading edge profile blade used to investigate numerically for enhance the aerodynamics performance of Wind turbine. Investigation were made to find pressure distribution over the Tubercle airfoils under various freestream velocity conditions such as 5 m/s, 10 m/s, 15 m/s and 20 m/s with different angle of attacks from −30° to 30° with the step of 5°. The Spalart–Allmaras turbulent model was used to carry out simulations in the ANSYS Fluent software. Therefore, the Coefficient of pressure distribution is calculated at peak and trough of the tubercle airfoil at different operating conditions and results are plotted in the graph. It is observed that pressure distribution varies drastically near the leading edge for all velocities. Analysis for different velocities with a wide range of angle of attacks are discussed and presented with relevant details.

Selection and Impact of an Aerofoil Leading Edge on Boundary Layer Transition

The choice of leading-edge aspect ratio (AR) plays a crucial role when planning boundary layer wind tunnel tests on a flat plate. Poor selection of the leading-edge profile hampers effectiveness of the experiment and increases testing costs associated with interchanging of leading edges to attain accurate results. Thus, the appropriate selection of the leading edge is a very crucial part of the wind tunnel experiment process. It is argued that the curvature of the leading edge and thus the AR is of paramount importance to achieve accurate results from the wind tunnel testing. In this project, seven different elliptical leading edges were tested, and their performance was compared with an ideal leading edge with zero thickness. Experiments and computation have been done for leading edges ranging from AR6 to AR20. Results were evaluated for boundary layer transition onset location, and it was found that AR20 has the least influence on the flow structure when compared to the ideal leading edge. A study of the flow structure at the stagnation point indicates an increase in adverse pressure gradient with an increase in the AR but also shows a decrease in the size of the stagnation region. The presence of a higher AR leading edge reduces the turbulent spot production rate, which is one of the primary causes of boundary layer transition. This paper presents a correlation that enables aerodynamicists to quantify the impact of the leading-edge AR on transition. A typical case is also presented to compare the relative performance of a wedge and the higher AR leading edge, which provides a choice between an elliptical or a wedge-shaped leading edge.

Numerical study on an optimum Q-switching profile for complete multipeak suppression in an actively Q-switched Ytterbium fibre laser

We propose an optimum Q-switching profile for complete suppression of the multi-peak phenomenon (MPP) without loss of pulse energy in an actively Q-switched ytterbium (Yb)-doped fibre laser. Most of the previously demonstrated approaches to suppress MPP have been based on adjusting of the rise time, and these rely on the assumption that the switching profile of the Q-switch has a trapezoidal temporal shape with a linear leading edge. These approaches leave one fundamental question as to whether or not there exists an optimum leading edge profile other than a simple linear one for complete suppression of MPP without loss of pulse energy. Through comparison among four different leading edge profiles. i.e. linear shape, sinusoidal function shape (increasing slope), sinusoidal function shape (decreasing slope), and composite function shape profiles, the proposed leading edge shape of a sinusoidal function (increasing slope) is shown to be capable of achieving complete suppression of MPP without loss of pulse energy under particular rise time conditions. It is shown that the use of a sinusoidal function (increasing slope) with a rise time of approximately 11 times the cavity round-trip time allows for the complete suppression of MPP without pulse energy loss in an exemplary, Q-switched, Yb-doped fibre Fabry–Perot laser.

Material parametric optimisation of wing leading edge profile against soft body impact

The present study aims to optimise the material parameters of the 2xxx series aluminium alloy used in aircraft wing leading edges to improve its mechanical properties against bird impact. For this study, a bird model is established and validated with an experiment test from literature and with a bird strike test on the wing leading edge. The significant material parameters which affect the energy absorption characteristics of the wing leading edge is selected from the comparison of parametric study results. Then the selected parameters are optimised and validated with bird impact analysis studies based on Taguchi’s L16 factorial design of experiments combined with grey relational analysis. The significant improvement in the mechanical properties, i.e. yield strength, ultimate tensile strength, and tensile toughness of the new optimised aluminium alloy has been proved with a series of uniaxial tension tests. The new alloy shows average property improvement up to 24.44% in tensile toughness and 19.4% in tensile strength than baseline alloy AA 2024-T3.

Design methodology of an osculating cone waverider with adjustable sweep and dihedral angles

When considering the practical engineering application of a waverider, the on-design and off-design aerodynamic characteristics of the design conditions, especially the lift-to-drag ratio and the stability, deserve attention. According to recently studies, the planform and rear sight shape of a waverider are closely related to the above aerodynamic performance. Thus, the planform leading-edge profile curve used to design the planform shape of a vehicle is applied to designing an osculating cone waverider. Two key parameters concerned in planform and rear sight shape, namely the plan view sweep angle of the leading edge and the dihedral angle of the underside are introduced to the waverider design process. Each parameter is inserted in the control curve equation. Especially, a parameterization scheme is put forward for the free adjustment of the sweep angle along the leading edge. Finally, three examples are generated for verification and investigation. After the verification process based on the inviscid flow field of one case, the influences of the sweep and dihedral angles on the lift-to-drag ratio and the lateral static stability are evaluated, and meaningful results are obtained. Based on these results, we can conclude that, considering the maximum lift-to-drag ratio, the sweep angle plays a role on the lift-to-drag ratio only at subsonic and trans/supersonic speed as a negligible effect is observed at hypersonic speeds, whereas the dihedral angle is seem to produce a relevant difference at hypersonic speeds. Considering the lateral static stability, the dihedral angles have more influence on the waverider than the sweep angles.

Aerodynamic Optimization of Unmanned Aerial Vehicle through Propeller Improvements

This paper aimed at presenting a number of suggested improvements that can enhance the performance of a multi-rotor Unmanned Aerial Vehicle. Evaluating each suggestion in terms of the added benefits and feasibility concluded a final choice, which is incorporating a sinusoidal leading-edge profile to the propeller. This choice was numerically investigated with ANSYS Fluent 16.1 through the SST K-Omega turbulence model. The performance of the modified propeller was assessed by comparing the lift and drag results to the same propeller with a straight leading-edge under the same conditions. Both models were studied at pre-stall and post-stall conditions to see the performance effect with respect to the angle of attack. The findings of this research showed 7% increase in the lift force and coefficient that were associated with the addition of the sinusoidal leading-edge including improved recovery from stall spanning from angle of attack that extends between 10° to 25°. This research also provides more insights into how the delayed stall and improved lift help the multirotor to extend flight time and carry heavier payloads. It allows for the exploration of the inner working of the sinusoidal leading-edge and its relationship with the flow field over the propeller.

Improvement of Hemodynamics in a Left Ventricular Assist Device Using Heuristic Aerodynamic Strategies to Redesign the Bladed Flow Domain

High levels of shear stress in the bladed flow domain of Left Ventricular Assist Devices (LVADs) lead to hemolysis, degradation of the von Willebrand factor and gastrointestinal bleeding. Optimal hemodynamics of the LVAD are crucial to minimizing the probability of these adverse events. In this study, a typical axial flow LVAD was redesigned using aerodynamics-based strategies to improve its hemodynamics and hence clinical outcomes for recipients. A reference LVAD was parametrically modeled using Computer Aided Design software. The baseline hemodynamic performance was then mapped using Computational Fluid Dynamics simulation of the blood flow. Subsequently, various heuristic, aerodynamic tactics were applied to iteratively redesign the flow domain. After each design change, a simulation was run to evaluate the hemodynamics of the LVAD. The ultimate modifications included streamlining the hub and shroud profiles, tuning the blade leading edge incidence angles, and sweeping back the leading edge profile of the blades. The optimized LVAD achieved significant hemodynamic improvements. The peak and area-averaged values of shear stress in the reference LVAD, 2300.43 Pa and 97.44 Pa, were reduced by 65.2% and 44.8%, respectively. At the rated flow of 0.1 kg/s and speed of 7000 rpm, the optimized design developed a slightly higher pressure rise, but within 4.5% of the reference design, in the same geometric envelope. Thus, the reduction in shear stress levels was achieved without compromise on the primary form and function of the LVAD. This study demonstrates that the application of heuristic, intensive aerodynamic design methods can significantly improve the hemodynamics of LVADs. Research suggests that patients implanted with such an optimized device would experience lower rates of hemolysis and gastrointestinal bleeding, as well as reduced degradation of the von Willebrand factor, improving outcomes post-implantation.

Cavitation erosion performance of CVD W/WC coatings

In the aviation industry, water droplet erosion (WDE) takes place when an aircraft takes off on as wet runway or flies through rain or clouds. The leading edge of turbofan blades suffers from high-speed (300–400 m/s) impingements of water droplets, resulting in material removal that subsequently changes the leading edge profile and surface roughness. This affects the aerodynamic performance of turbofan blades, which eventually leads to efficiency drop of the aircraft engine and the need to replace and/or recondition the blades. A coating solution is targeted, such that, not only that it resists the high impact pressure but also inhibits stress wave reinforcements at the coating-substrate or interlayers interfaces. Past studies indicate similar damage mechanisms to WDE are generated by cavitation erosion (CE) during the early stages (incubation). Hence, CE is introduced in this study to predict the WDE performance. The coatings studied were nanostructured CVD tungsten/tungsten carbide coatings, either hierarchical or monotonic in design, on Ti6Al4V alloy grade 5 substrates. In-depth understanding on the coating damage mechanisms are established by correlating the coating performance with microstructure, crystallographic texture, interface design, coating deposition conditions and mechanical properties for the first time. A particular crystalline texture was found that gives optimum performance. The effect of the initial coating topography on the CE performance is effectively characterised by the surface parameters Ssk and Sku. The damage was found to initiate at the grain boundaries of the exposed surfaces. The hierarchical coating microstructure demonstrated enhancement in CE performance compared to a monotonic columnar grain structure. Additionally, it is found that the coating performance under dynamic compressive loadings could not be predicted by a simple H/E approaches. However, combining the H/E ratios with the factors of microstructure and crystal orientations might further facilitate the understanding of coating performances along with better understanding of the role of compressive residual stresses and stress waves propagation or reinforcement through coating depth and at the top surface of the coating.

Physical mechanisms and performance of slitted leading-edge profiles for the reduction of broadband aerofoil interaction noise

Aerofoil Turbulence Interaction (ATI) noise is an inviscid phenomenon generated by the impingement of turbulent flows onto the leading-edge of an aerofoil. This paper deals with a novel leading-edge serration geometry, composed of narrow slits, to reduce ATI noise. These profiles have been recently found to provide significantly better noise reductions than conventional leading edge geometries. A numerical and analytic investigation is performed into the mechanism and performance of its noise reduction. The far-field radiation is shown to be influenced by a system of induced vortices affecting the distribution of sources on the flat-plate and by destructive interference between the two sources generated at both ends of the slit. A simple two-source model is developed to predict the far-field noise reduction obtained and compared to straight leading-edge aerofoils.

Sensitivity investigation of a subsonic cascade performance to geometric deviations based on statistical method

This paper has established an evaluation system for the sensitivity analysis of cascade/compressor aerodynamic performance to geometric deviations. The system includes blade profile parameterization with non-uniform rational B-spline (NURBS), uniform Latin hypercube sampling in association with Monte Carlo algorithm and statistical investigation methods. The sensitivity of a subsonic cascade performance to its geometric deviations is investigated under different typical inflow conditions. Results show that there is an approximately linear relationship between the geometric deviations and the aerodynamic parameters. The total pressure loss coefficient is the most sensitive to the leading edge profile deviation at i=2°. However the suction profile deviation and the leading edge profile deviation dominate the total pressure loss when the incidences are i = −4° and i = −8°. The blocking effect of the increased leading edge profile moves forward the separation point of the boundary layer. Therefore the scale of the separation vortex is enlarged, the total pressure loss is increased at i = 2° condition. Regarding i = −8°, the enlarged suction profile deviation reduces the circumferential static pressure gradient, resulting in an increase of the scale of separation vortex on the pressure side. The work is helpful to robust design of compressor blade profile and manufacturing & maintenance techniques of compressor blades.

Leading-Edge Profiles for the Reduction of Airfoil Interaction Noise

Airfoils operating in a turbulent flow are an efficient source of noise radiation by scattering vorticity into sound at the leading edge. Much work has been undertaken demonstrating the effectiveness by which serrations, or undulations, introduced onto the leading edge can substantially reduce broadband leading-edge interaction noise. However, most of this work is focused on sinusoidal leading-edge serration profiles. In this paper, a family of serration profiles is proposed that is capable of providing significantly greater noise reductions than single-wavelength serrations at optimal conditions. This new family of profiles will be shown to reduce interaction noise through a fundamentally different noise reduction mechanism than conventional single-wavelength profiles. Unlike single-wavelength profiles, which produce a single compact dominant source region per serration wavelength, these new profiles are designed to produce two or more dominant compact sources per serration wavelength of roughly the same source strength that are separated in the streamwise direction. Because these sources are arranged to be closer together than the turbulence length scale, they are highly coherent and, at certain frequencies, radiate exactly 180 deg out of phase, leading to very high levels of noise reduction in the far field. The experimental noise reduction spectra are first compared against an analytic model obtained as a solution of the acoustic wave equation using the Wiener–Hopf technique. This approach focuses solely on solving for an acoustic field, and not for any secondary vorticity induced by the edge. As such, this comparison, which shows disagreement, proves that secondary vorticity is a dominant mechanism for these new profiles. A simple supplementary analytical model has therefore been developed to explain this noise reduction mechanism for these new profiles, based on interference between sources distributed along the leading edge. Good qualitative agreement is obtained with the experimental results.

Improvement of leading-edge accuracy by optimizing the cathode design plane in electrochemical machining of a twisted blade

Cathode design plays an important role in the electrochemical machining of aero engine blades and is a core issue influencing machining accuracy. Precision electrochemical machining of the leading edge of a twisted blade is particularly difficult. To improve the electrochemical machining accuracy of the leading edge, this article deals with cathode design by optimizing the design plane based on the three-dimensional potential distribution in the inter-electrode gap. A mathematical model is established according to the electrochemical machining shaping law, and the formation of the blade leading edge is simulated using ANSYS. The simulation results show that the blade leading-edge profile obtained with the optimized planar cathode is more consistent with the blade model profile. The optimized planar cathode and a non-optimized planar cathode are designed and a series of corresponding electrochemical machining experiments is carried out. The experiments show that the electrochemical machining process is stable and that the surface quality near the leading edge of the samples is slightly better than that of the body surface. Compared with the non-optimized planar cathode, the allowance difference at the leading-edge vertex is decreased by 0.062 mm. Using the optimized planar cathode allows fabrication of a workpiece whose shape is similar to that of the designed twisted blade.