Numerical Study on the Duct Noise Control of Single-Stage Axial Flow Fan with Wave Leading Edge Stator Blade Configurations

This study focuses on a single-stage axial flow fan, investigating the effect of three kinds of wave leading edge stator blades on its noise reduction. The DDES method and the duct acoustic analogy theory based on the penetrable data surface were used for noise prediction. The results showed that the three kinds of wave leading edge blades were effective in reducing the rotor-stator interaction tonal noise and also have a certain inhibitory effect on broadband noise. The A10W15 stator blade can effectively reduce broadband noise in the frequency range of 2200 - 4200 Hz. When the amplitude is increased to 20, the noise reduction effect is further enhanced. However, when the amplitude is increased to 30, the broadband noise reduction effect is no longer significant. Further research shows that the wave leading edge stator blades can significantly change the pressure fluctuation distribution on the leading edge and suction surface, which control the modal energy distribution. Finally, this paper analyzed multiple factors affecting the broadband noise reduction, such as the noise source cut-off and cut-on effect and correlation. The purpose of this paper is to explore the laws of the influence of wave leading edge blades on the duct noise of real fan, and to reveal its noise control mechanism. .

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.

High-Velocity Impact Studies on Scaled Leading Edges of Horizontal Tail with Smart Composite Layers

Bird strike studies on typical aluminium leading edges of the Horizontal Tail (HT) with and without Glass Fibre Shape Memory Polymer (GF-SMP) layers are carried out. A one-fifth scaled model of HT is designed and fabricated. The parameters like bird dimension and energy requirements are accordingly scaled to conduct the bird strike tests. Two leading-edge components have been prepared, namely one with AL 2024-T3 aluminium alloy and the other specimen of the same dimension and material, additionally having GF-SMP composite layers inside the metallic leading edge, in order to enhance its impact resistance. Bird strike experiments are performed on both the specimens, impacting at the centre of the leading edge in the nose tip region with an impact velocity of 115 m/s. The test component is instrumented with linear post-yield strain gauges on the top side and the PZT sensors on the bottom. Furthermore, the impact scenario is monitored using a high-speed camera at 7000 fps. The bird strike event is simulated by an equation of state model, in which the mass of the bird is idealized using smooth particle hydrodynamics element in PAMCRASH? explicit solver. The strain magnitude and its pattern including time duration are found to be in a good correlation between test and simulation. Key metrics are evaluated to devise an SHM scheme for the load and impact event monitoring using strain gauges and PZT sensors. GF-SMP layers have improved the impact resistance of the aluminium leading edge which is certainly encouraging towards finding a novel solution for the high-velocity impact.

Piezoelectric resonant ice protection systems–Part1/2:Prediction of power requirement for de-icing a NACA 0024 leading edge

This paper proposes a numerical method to analyze the ice protection capability and predict the power requirements of a piezoelectric resonant de-icing system.The method is based on a coupled electro-mechanical finite element analysis which enables the fast computation of the modes of resonance of interest to de-ice curved surfaces and the estimation of the input voltage and current required for a given configuration(defined by its mode,actuator location,ice deposit,etc.).Eventually,the electric power to be supplied can be also assessed.The method is applied to a NACA 0024 leading edge equipped with piezoelectric actuators.First,two extension modes are analyzed and compared with respect to their efficiency and power requirements.Then,tests are carried out in an icing tunnel to verify the effectiveness of the piezoelectric ice protection system and the predictions of the maximal required power.The system allows de-icing the leading edge in less than 2 s for a glaze ice deposit.

Synthesis and performance characterization of Hafnium-based multilayer coating applied over carbon/carbon composites with sharp leading edge

Carbon/carbon(C/C)composites have been acknowledged as potential candidates in aerospace vehicles,but their oxygen sensitivity still remains an enormous challenge.In this work,a novel multilayer coating consisted of HfC-2.5 mol.%Hf_(6)Ta_(2)O_(17),HfC-40 mol.%SiC,HfC-2.5 mol.%Hf_(6)Ta_(2)O_(17) and HfC-60 mol.%SiC sublayers from surface to inside was designed and fabricated on the surface of C/C composites with sharp leading edge by plasma spraying.Its ablation resistance was assessed using oxyacetylene torch with a maximum temperature over 2300℃ and compared with monolayered coatings.The multilayer coating revealed preferable ablation retardation capacity evidenced by its integrated profile and less flaw quantity.Such benefits were primarily stemmed from the effective structural design and rational material selection.The former was able to reduce the thermal stress within the ablated scale,the latter contributed to rising the high-temperature resistance and oxygen barrier ability of the coating.

Damage sensitivity of a wing-type leading edge structure impacted by a bird

On the windward side of an aircraft,the components with higher probability of impact with birds are the wing-type leading edge structures,such as the wing and tail.A study on the damage sensitivity of a wing-type leading edge structure under bird strikes was presented in this paper.First,a bird strike test was carried out on a wing.The principles of the bird strike test equipment and method were introduced in detail,including the bird strike test system,bird projectile production process and data acquisition system.The dynamic strain measurement results,the high-speed camera videos,and the final deformation and damage morphology observations of the structure were obtained.Based on the coupled Smooth Particle Hydrodynamics(SPH)-Finite Element Method(FEM),the commercial software PAM-CRASH was used to simulate the process of a bird strike with the wing.The good agreement between the finite element simulation results and the experimental results shows that the calculation method and the numerical model presented in this paper were reasonable.On this basis,wing-type leading edge structures can be designed by adding triangular support.The bird strike resistances of an original structure and improved structure were studied by numerical simulation.The calculated results show that the improved wing-type leading edge structure is less damaged than the original structure under bird strike.The improved leading edge structure satisfied the anti-bird strike airworthiness requirements,as the thickness of the triangular support was 1.2 mm,and the weight of the structure was reduced by 0.87 kg compared with the original structure.This indicated that the bird strike resistance of the improved structure is better than that of the original structure,and the improved design of the wing-type leading edge structure presented in this paper is reasonable.

Comparative study of two lay-up sequence dispositions for flexible skin design of morphing leading edge

Morphing leading edge has great potential for noise abatement and aerodynamic efficiency improvement.The drooping effect is realized by bending of the flexible skin which encloses to form the leading edge.Since the flexible skin is often made of composite laminates of Glass Fiber Reinforced Plastics(GFRP),the lay-up sequences have become the determinant,which affects not only the morphing quality but also the manufacturing complexity.Two optimizing methods of layup sequences are comparatively studied.In the first method,the laminal quantities in 0,±45and 90vary independently,while in the second one,the concept of isotropic laminate unit[0/45/45/90]s is employed and the unit quantity is the unique variable.Final evaluation demonstrates that for both methods there is insignificant impact to the overall morphing quality;however,specific concern is equally necessary for these two methods to the tip of the leading edge where the skin is at its minimum thickness and bears the most severe bending deformation.In terms of computational efficiency and post-processing labor,the second method has better performance.

Experimental Investigation on the Adiabatic Film Effectiveness for Counter-Inclined Simple and Laid-Back Film-Holes of Leading Edge

The adiabatic film effectivenessηof the counter-inclined film-holes fed by varying internal coolant intake on the turbine vane leading edge model was experimentally investigated.A semi-cylinder model was adopted to model the vane leading edge which was arranged with two-row holes,which located at±15°on both sides.The four Leading edge model with the combinations of hole-shape(simple holes and laid-back holes)and intake structure(plenum and impingement)were tested under four blowing ratios M of 0.5,1.0,1.5,and 2.0.Theηcontours were obtained by the transient measurement technique based on double thermochromic liquid-crystals.The results present that theηis sensitive to the M for the four studied leading edge cases.The addition of impingement enhances theηfor the two studied holes.The film jets make the coolant-flow closed to the target surface,resulting in higherηunder lower M.The core with higherηappears in the downstream area of hole-exit.Theηenhancement can be provided to almost the identical level by adding the impingement-holes and improving the hole-exit shaping in most areas.With increasing M,the jets with stronger exit normal momentum penetrate into the main-flow.The impingement addition may be a more effective program to upgrade theηrelatively to the exit shaping under larger M.Besides,the laid-back holes with impingement case produce the highest film cooling performance among the four cases,providing great potential in the leading edge especially under larger M.

Global cavitation patterns and corresponding hydrodynamics of the hydrofoil with leading edge roughness

The objective of this paper is to experimentally investigate the cavitation patterns and corresponding hydrodynamics of the hydrofoil with leading edge roughness.The aims are to(1)understand the effect of the leading edge roughness on the hydrodynamic performance,and(2)have a good knowledge of the interaction between the leading edge roughness and the cavitation patterns.Experimental results are indicated for the NACA 66 hydrofoils with and without leading edge roughness at different incidence angles for sub and cavitation conditions.The experiments are conducted in the EPFL high-speed cavitation tunnel(Avellan 2015).The results showed that the leading edge roughness has a significant effect on the hydrodynamic performance at the sub cavitation,suppressing the formation of the incipient cavitation.The lift coefficient of the hydrofoil without leading edge roughness is larger than that of the hydrofoil with leading edge roughness,while for the drag coefficients,the results are contrary for the lift coefficient,and the maximum lift-to-drag ratio angle is delayed for the hydrofoil with leading edge roughness.The leading edge roughness modified the local pressure distribution at the leading edge region,which in turn significantly increased the minimum pressure coefficient,hence the incipient cavitation number of the hydrofoil with leading edge roughness.The formation and evolution of the transient cavity for the cloud cavitation is little affected by the leading edge roughness.

Ablation behavior of(ZrC/SiC)_(3)alternate coating prepared on sharp leading edge C/C composites by CVD

A(ZrC/SiC)_(3)alternate coating was deposited on sharp leading edge(SLE)C/C composites by chemical vapor deposition(CVD).The ablation behavior was examined via oxyacetylene torch with heat flux of 2.38 MW/m^2.The results indicated that the alternate coating exhibited great ablation resistance,providing an effective protection for C/C composites.In initial rapid heating stage,the(ZrC/SiC)_(3) alternate coating can relieve thermal stress,avoiding the peeling of coating and keeping an intact coating structure.In subsequent ablation,the Si C layers in central region were consumed rapidly,leaving layered interspaces.Three stacked ZrO_(2) layers were reserved with the assistance of the release of thermal stress by interspaces,offering a great anti-scouring effect.In transition and border regions,the alternate Si C layers can delay oxygen erosion of inner coating and C/C substrate by the formation of SiO_(2).It is believed that the results would be helpful for the design and application of anti-ablation coatings on SLE C/C composites.

Measuring flow velocity on frozen and non-frozen slopes of black soil through leading edge method

Flow velocity is a major parameter related to hillslope hydrodynamics erosion.This study aims to measure flow velocity over frozen and non-frozen slopes through leading edge method before being calibrated with accurate flow velocity to determine the correct coefficient for convenience of flow velocity measurement.Laboratory experiments were conducted on frozen and non-frozen soil slopes with flumes involving four slope gradients of 5°,10°,15°,and 20°and three flow rates of 1,2,and 4 L/min with a flume of 6 m long and 0.1 m wide.The measurements were made with a stopwatch to record the time duration that the water flow ran over the rill segments of 2,4 and 6 m long.Accurate flow velocity was measured with electrolyte trace method,under pulse boundary condition.The leading edge and accurate flow velocities were used to determine the correction coefficient to convert the former to the latter.Results showed that the correction coefficient on frozen soil slope was 0.81 with a coefficient of determination(R2)of 0.99.The correction coefficient on non-frozen soil slope was 0.79 with R2 of 0.98.A coefficient of 0.8 was applicable to both soil surface conditions.The accurate velocities on the four frozen black soil slopes were approximately 30%,54%,71%,and 91%higher than those on non-frozen soil slopes.By contrast,the leading edge flow velocities on the frozen soil slopes were 23%,54%,67%,and 84%higher than those on non-frozen soil slopes.The flow velocities on frozen soil slopes increased with flow rate at all four slopes,but they increased from 5 to 15°before getting stabilized.Therefore,rill flow velocity can be effectively measured with leading edge method by multiplying the leading edge velocity with a correction coefficient of 0.80.This study provides a strategy to measure rill flow velocity for studies on soil erosion mechanisms.

Numerical investigation on heat transfer in an advanced new leading edge impingement cooling configuration

It is known that the leading edge has the most critical heat transfer area of a gas turbine blade.The highest heat transfer rates on the airfoil can always be found on the stagnation region of the leading edge.In order to further improve the gas turbine thermal efficiency the development of more advanced internal cooling configurations at leading edge is very necessary.As the state of the art leading edge cooling configuration a concave channel with multi inline jets has been widely used in most of the blades.However,this kind of configuration also generates strong spent flow,which shifts the impingement off the stagnation point and weakens the impingement heat transfer.In order to solve this problem a new internal cooling configuration using double swirl chambers in gas turbine leading edge has been developed and introduced in this paper.The double swirl chambers cooling(DSC)technology is introduced by the authors and contributes a significant enhancement of heat transfer due to the generation of two anti-rotated swirls.In DSC-cooling,the reattachment of the swirl flows always occurs in the middle of the chamber,which results in a linear impingement effect.Compared with the reference standard impingement cooling configuration this new cooling system provides a much more uniform heat transfer distribution in the chamber axial direction and also provides a much higher heat transfer rate.In this study,the influences of different geometrical parameters e.g.merging ratio of two cylinder channels,the jet inlet hole configurations and radius of blunt protuberances in DSC have been investigated numerically.The results show that in the DSC cooling system the jet inlet hole configurations have large influences on the thermal performance.The rectangular inlet holes,especially those with higher aspect ratios,show much better heat transfer enhancement than the round inlet holes.However,as the price for it the total pressure drop is increased.Using blunt protuberances instead of sharp edges in the DSC cooling can improve the heat transfer enhancement and reduce the total pressure drop.

Method for utilizing PIV to investigate high curvature and acceleration boundary layer flows around the compressor blade leading edge

Particle Image Velocimetry(PIV)is a well-developed and contactless technique in experimental fluid mechanics,but the strong velocity gradient and streamline curvature near the wall substantially limits its accuracy improvement.This paper presents a data processing procedure combining conventional PIV and newly developed Mirror Interchange(MI)based Interface-PIV for the measurement of the boundary layer parameter development in the blade leading edge region.The synthetic particle images are used to analyze the measurement errors in the entire procedure.Overall,three types of errors,namely the errors caused by the Window Deformation Iterative Multigrid(WIDIM)algorithm,the discrete data interpolation and integration,and the wall offset uncertainty,comprise the main measurement error.Specifically,the errors due to the discrete data interpolation and integration and the WIDIM algorithm comprise the mean bias,which can be corrected through the error analysis method proposed in the present work.Meanwhile,the errors due to the WIDIM algorithm and the wall offset uncertainty contribute to the measurement uncertainty.Computational fluid dynamics-based synthetic particle flows were generated to verify the newly developed PIV data processing procedure and the corresponding error analysis method.Results showed that the data processing method could improve the accuracy of PIV measurements for boundary layer flows with high curvature and acceleration and even with significant flow separation bubbles.Finally,the data processing method is also applied in a PIV experiment to investigate the boundary layer flows around a compressor blade leading edge,and several credible boundary flow parameters were obtained.

A Review of the Attachment Line Instability for Hybrid Laminar Flow Control

This paper focuses on the investigation of the attachment line instability for Hybrid Laminar Flow Control(HLFC),one of the most promising drag reduction technologies for modern transport aircraft respect to high Reynolds numbers and large sweep angles.The attachment line instability also plays an important role during laminar-turbulent transition control and HLFC design on a swept wing.The overview of historical research is presented and knowledge gaps are pointed out as the conclusion.

Cooling Performance of the Endwall Vertical Hole Considering the Interaction between Cooling Jet and Leading-Edge Horseshoe Vortex

Interaction between the coolant and the secondary flow plays an important role in endwall cooling performance.For the leading-edge region,oncoming main flow inside the boundary layer impinges onto the vane leading edge and turns into the horseshoe vortex.Horseshoe vortex entrains coolant off the surface,thus posing severe challenges to the cooling design there.Based on analyses on the leading-edge vortex formation mechanism,a new kind of endwall film cooling design,vertical hole upstream of the saddle point,is proposed to obtain more uniform film coverage over the vane/endwall junction region.Coolant injected from the vertical hole can pass over the horseshoe vortex and impinge around the stagnation line on the vane leading edge.Uniform film coverage can be obtained around the vane leading edge where coolant clings to the endwall surface due to the span-wise pressure gradient of the stagnation region.Numerical simulations are conducted about the cooling performance of two main kinds of both isotropic and anisotropic hole geometries for the endwall and vane surface.Results come that the anisotropic hole shows significant advantages over the isotropic one because it suppresses the symmetrical kidney vortices thus weakening the mixture with high-temperature gas.Blowing ratio(M)effect is analyzed and conclusions are drawn that the cooling performance of the endwall around the leading edge is sensitive to M and adiabatic film cooling effectiveness peaks at about M=2.0.Better cooling performance over the vane corner region can be obtained when M gets even higher while the effective film coverage area shrinks.Apart from that,the phenomenon of phantom cooling on the upper triangular region of the suction surface can be observed when coolant on the endwall is entrained by the vortex formed at the corner of the leading edge.

Retrieval of Sea Surface Height from CYGNSS Data with Tropospheric Delay

An analysis of the delay Doppler maps(DDMs) data from the CYGNSS satellites is implemented to derive the sea surface height(SSH). An SSH estimation algorithm, the leading edge derivation(LED) method which is applied to the delay waveforms, is applied to the DDMs, while the tropospheric delay methods, the Saastamoinen method(SM)and the numerical method(NM) are used. The results show that when the SSH from Jason-2 is referred to as the truth, if the tropospheric delay is corrected, the SSH bias can decrease. The resulted SSH bias from the Jason-2 SSH by the LED retrieval method is of order meter. The resulted SSH deviation from the truth by the NM scheme is half as small as that by the SM scheme. Since the SM scheme is not applicable to the nonhydrostatical condition, the resulted bias is larger.The work can be applied to the Beidou system in the future.

Features of Operation of Bifilar Cooper and Tesla Coils in Pulse Regime

The characteristic features of operation in a pulsed regime of bifilar Cooper and Tesla coils during magnetic pulse processing and heating of the environment are considered using the dependence of the maximum amplitude at the leading edge of the magnetic pulse on its time duration τ. The spatial distribution of the magnetic induction lines B inside and around the Cooper coil is given, where, unlike the Tesla coil, the maximum values of B arise in the extreme planes of the coil, and its central plane is zero. The defining advantages of new methods of magnetic pulse processing and heating of the environment are considered: the dependence at τ → 0;the exchange of energy between the magnetic pulse and the environment;periodic sequence of series of unipolar magnetic pulses at various processing modes. It is shown that 1) for electric fields Eout = 1010 – 1012V/m, arising at the leading edge of a magnetic pulse with duration 10-5 – 10-7 s, in the deformation fractal space the electrodynamics of these fields is nonlinear;2) inside the Tesla coil, in the package of conducting tapes and tubes, the pumping energy from the pulsed field Eout is mainly dissipated in the skin layer in the form of refractory coatings and heats the environment at all stages of plastic deformation of workpieces and heating elements up to the collapse of unstable microcracks. The coefficient of conversion of the pump energy in the pulsed regime with respect to the constant current regime is found.

Design and validation of a variable camber wing structure

Variable camber wing technology is one of the important development trends of green aviation at present.Through smooth,seamless,continuous and adaptive change of wing camber,the aerodynamic performance is improved in achieving increase in lift and reduction in resistance and noise.Based on the aerodynamic validation model CAE-AVM,Chinese Aeronautical Establishment(CAE)has carried out the design and validation of a variable camber wing,proposed an aerodynamic deformation matrix for the leading and trailing edges of aircraft wings in takeoff,landing and cruise conditions.Various structures and driving schemes are compared,and several key technology problems of leading and trailing edge deformation are solved.A full-size leading edge wind tunnel test piece with a span of 2.7 m and a trailing edge ground function test piece are developed.The deformation and shape maintenance capabilities of the leading edge is verified under real wind load conditions,and the load bearing and deformation capabilities of the trailing edge is verified under simulated follow-on load.The results indicate that the leading and trailing edges of the variable camber wing can achieve the required deformation angle and have a certain load-bearing capacity.Our study can provide some insights into the application of variable camber wing technology for civil aircraft.

Development of a deviation package method for low-cost robust optimization in compressor blade design

Manufacture variations can greatly increase the performance variability of compressor blades. Current robust design optimization methods have a critical role in reducing the adverse impact of the variations, but can be affected by errors if the assumptions of the deviation models and distribution parameters are inaccurate. A new approach for robust design optimization without the employment of the deviation models is proposed. The deviation package method and the interval estimation method are exploited in this new approach. Simultaneously, a stratified strategy is used to reduce the computational cost and assure the optimization accuracy. The test case employed for this study is a typical transonic compressor blade profile, which resembles most of the manufacture features of modern compressor blades. A set of 96 newly manufactured blades was measured using a coordinate measurement machine to obtain the manufacture variations and produce a deviation package. The optimization results show that the scatter of the aerodynamic performance for the optimal robust design is 20% less than the baseline value. By comparing the optimization results obtained from the deviation package method with those obtained from widely-used methods employing the deviation model, the efficiency and accuracy of the deviation package method are demonstrated. Finally, the physical mechanisms that control the robustness of different designs were further investigated, and some statistical laws of robust design were extracted.

Study on segmented distribution for reliability evaluation

In practice, the failure rate of most equipment exhibits different tendencies at different stages and even its failure rate curve behaves a multimodal trace during its life cycle. As a result,traditionally evaluating the reliability of equipment with a single model may lead to severer errors.However, if lifetime is divided into several different intervals according to the characteristics of its failure rate, piecewise fitting can more accurately approximate the failure rate of equipment. Therefore, in this paper, failure rate is regarded as a piecewise function, and two kinds of segmented distribution are put forward to evaluate reliability. In order to estimate parameters in the segmented reliability function, Bayesian estimation and maximum likelihood estimation(MLE) of the segmented distribution are discussed in this paper. Since traditional information criterion is not suitable for the segmented distribution, an improved information criterion is proposed to test and evaluate the segmented reliability model in this paper. After a great deal of testing and verification,the segmented reliability model and its estimation methods presented in this paper are proven more efficient and accurate than the traditional non-segmented single model, especially when the change of the failure rate is time-phased or multimodal. The significant performance of the segmented reliability model in evaluating reliability of proximity sensors of leading-edge flap in civil aircraft indicates that the segmented distribution and its estimation method in this paper could be useful and accurate.