scholarly journals A Numerical Study of Aerodynamic Performance and Noise of a Bionic Airfoil Based on Owl Wing

2014 ◽  
Vol 6 ◽  
pp. 859308 ◽  
Author(s):  
Xiaomin Liu ◽  
Xiang Liu
Keyword(s):  
Reynolds Number ◽  
Unsteady Flow ◽  
Noise Reduction ◽  
Numerical Study ◽  
Aerodynamic Performance ◽  
Centrifugal Fan ◽  
Surface Geometry ◽  
Airfoil Surface ◽  
Acoustic Sources ◽  
Bionic Airfoil

Noise reduction and efficiency enhancement are the two important directions in the development of the multiblade centrifugal fan. In this study, we attempt to develop a bionic airfoil based on the owl wing and investigate its aerodynamic performance and noise-reduction mechanism at the relatively low Reynolds number. Firstly, according to the geometric characteristics of the owl wing, a bionic airfoil is constructed as the object of study at Reynolds number of 12,300. Secondly, the large eddy simulation (LES) with the Smagorinsky model is adopted to numerically simulate the unsteady flow fields around the bionic airfoil and the standard NACA0006 airfoil. And then, the acoustic sources are extracted from the unsteady flow field data, and the Ffowcs Williams-Hawkings (FW-H) equation based on Lighthill's acoustic theory is solved to predict the propagation of these acoustic sources. The numerical results show that the lift-to-drag ratio of bionic airfoil is higher than that of the traditional NACA 0006 airfoil because of its deeply concave lower surface geometry. Finally, the sound field of the bionic airfoil is analyzed in detail. The distribution of the A-weighted sound pressure levels, the scaled directivity of the sound, and the distribution of dP/dt on the airfoil surface are provided so that the characteristics of the acoustic sources could be revealed.

Numerical Study of Airfoil Tonal Noise Reduction using Segmented Elastic Panel Configuration

2021 ◽  
Vol 263 (4) ◽  
pp. 2916-2929
Author(s):  
Arif Muhammad Irsalan ◽  
Garret C. Y. Lam ◽  
Randolph C. K. Leung
Keyword(s):  
Reynolds Number ◽  
Noise Reduction ◽  
Numerical Study ◽  
Separation Bubble ◽  
Low Reynolds Number ◽  
Flow Characteristics ◽  
Tonal Noise ◽  
Airfoil Surface ◽  
Passive Method ◽  
Low Reynolds

In this paper, a novel passive method for airfoil tonal noise reduction is proposed using a configuration of two segmented elastic panels mounted on the airfoil. Numerical investigation using perturbation evolution method is carried out at a low Reynolds number based on airfoil chord of 5x10 and an angle of attack of 5. The passive method of employing a single panel has shown promising tonal noise reduction capabilities where the resonating panel located just ahead of the sharp growth of boundary layer instability within the airfoil separation bubble provided the strongest reduction of instabilities and noise reduction up to 3 dB has been achieved. The idea is extended in the present study by employing a two-panel configuration based on the localized flow characteristics over the airfoil surface. Five different panel configurations are designed and their effectiveness in terms of tonal noise reduction is evaluated and compared with baseline configuration. The azimuth and spectral analyses indicate the different extent of noise reduction for each configuration and even noise amplification in one of them. A significant noise reduction up to 8 dB is observed for the optimum configuration indicating the effectiveness of this novel method for devices operating at low Reynolds number.

Numerical study on the airfoil self-noise of three owl-based wings with the trailing-edge serrations

2021 ◽  
pp. 095441002098822
Author(s):  
Dian Li ◽  
Xiaomin Liu ◽  
Lei Wang ◽  
Fujia Hu ◽  
Guang Xi
Keyword(s):  
Flow Field ◽  
Noise Reduction ◽  
Numerical Study ◽  
Barn Owl ◽  
Aerodynamic Noise ◽  
Frequency Noise ◽  
Trailing Edge ◽  
Reduction Mechanisms ◽  
Trailing Edge Serrations ◽  
Bionic Airfoil

Previous publications have summarized that three special morphological structures of owl wing could reduce aerodynamic noise under low Reynolds number flows effectively. However, the coupling noise-reduction mechanism of bionic airfoil with trailing-edge serrations is poorly understood. Furthermore, while the bionic airfoil extracted from natural owl wing shows remarkable noise-reduction characteristics, the shape of the owl-based airfoils reconstructed by different researchers has some differences, which leads to diversity in the potential noise-reduction mechanisms. In this article, three kinds of owl-based airfoils with trailing-edge serrations are investigated to reveal the potential noise-reduction mechanisms, and a clean airfoil based on barn owl is utilized as a reference to make a comparison. The instantaneous flow field and sound field around the three-dimensional serrated airfoils are simulated by using incompressible large eddy simulation coupled with the FW-H equation. The results of unsteady flow field show that the flow field of Owl B exhibits stronger and wider-scale turbulent velocity fluctuation than that of other airfoils, which may be the potential reason for the greater noise generation of Owl B. The scale and magnitude of alternating mean convective velocity distribution dominates the noise-reduction effect of trailing-edge serrations. The noise-reduction characteristic of Owl C outperforms that of Barn owl, which suggests that the trailing-edge serrations can suppress vortex shedding noise of flow field effectively. The trailing-edge serrations mainly suppress the low-frequency noise of the airfoil. The trailing-edge serration can suppress turbulent noise by weakening pressure fluctuation.

scholarly journals Numerical study of unsteady flow and exciting force for swept turbomachinery blades

2016 ◽  
Vol 20 (suppl. 3) ◽  
pp. 669-676
Author(s):  
Di Zhang ◽  
Ma Jiao-Bin ◽  
Qi Jing
Keyword(s):  
Boundary Layer ◽  
Unsteady Flow ◽  
Pressure Fluctuation ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Aerodynamic Performance ◽  
Rotor Blades ◽  
Stable Operation ◽  
Straight Blade ◽  
Excitation Force

The aerodynamic performance of blade affects the vibration characteristics and stable operation of turbomachinery closely. The aerodynamic performance of turbine stage can be improved by using swept blade. In this paper, the RANS method and the RNG k-? turbulence mode were adopted to investigate the unsteady flow characteristics and excitation force of swept blade stage. According to the results, for the swept blade, the fluid of boundary layer shifts in radial direction due to the influence of geometric construction. It is observed that there is similar wake development for several kinds of stators, and the wake has a notable effect on the boundary layer of the rotor blades. When compared with straight blade, pressure fluctuation of forward-swept blade is decreased while the pressure fluctuation of backward-swept blade is increased. The axial and tangential fundamental frequency excitation force factors of 15?forward-swept blade are 0.139 and 0.052 respectively, which are the least, and all excitation force factors are in the normal range. The excitation factor of the forward-swept blade is decreased compared with straight blade, and the decreasing percentage is closely related to the swept angle. As for backward-swept blades, the situation is the other way around. Additionally, the change of axial excitation factor is more obvious. So the vibration reduction performance of forward-swept blade is better.

scholarly journals Experimental Study of Airfoil Leading Edge Combs for Turbulence Interaction Noise Reduction

Acoustics ◽  
2020 ◽  
Vol 2 (2) ◽  
pp. 207-223 ◽  
Author(s):  
Thomas Geyer ◽  
Sahan Wasala ◽  
Ennes Sarradj
Keyword(s):  
Experimental Study ◽  
Noise Reduction ◽  
Microphone Array ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Aerodynamic Performance ◽  
Airfoil Surface ◽  
Low Frequencies ◽  
High Frequencies ◽  
Turbulent Eddies

The interaction of a turbulent flow with the leading edge of a blade is a main noise source mechanism for fans and wind turbines. Motivated by the silent flight of owls, the present paper describes an experimental study performed to explore the noise-reducing effect of comb-like extensions, which are fixed to the leading edge of a low-speed airfoil. The measurements took place in an aeroacoustic wind tunnel using the microphone array technique, while the aerodynamic performance of the modified airfoils was captured simultaneously. It was found that the comb structures lead to a noise reduction at low frequencies, while the noise at high frequencies slightly increases. The most likely reasons for this frequency shift are that the teeth of the combs break up large incoming turbulent eddies into smaller ones or that they shift turbulent eddies away from the airfoil surface, thereby reducing pressure fluctuations acting on the airfoil. The aerodynamic performance does not change significantly.

scholarly journals Numerical Study of Effect of Sawtooth Riblets on Low-Reynolds-Number Airfoil Flow Characteristic and Aerodynamic Performance

Processes ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 2102
Author(s):  
Xiaopei Yang ◽  
Jun Wang ◽  
Boyan Jiang ◽  
Zhi’ang Li ◽  
Qianhao Xiao
Keyword(s):  
Reynolds Number ◽  
Drag Reduction ◽  
Numerical Study ◽  
Low Reynolds Number ◽  
Aerodynamic Performance ◽  
Operating Conditions ◽  
Viscous Drag ◽  
Airfoil Flow ◽  
Low Reynolds ◽  
Reduction Effect

Riblets with an appropriate size can effectively restrain turbulent boundary layer thickness and reduce viscous drag, but the effects of riblets strongly depend on the appearance of the fabric that is to be applied and its operating conditions. In this study, in order to improve the aerodynamic performance of a low-pressure fan by using riblet technology, sawtooth riblets on NACA4412 airfoil are examined at the low Reynolds number of 1 × 105, and the airfoil is operated at angles of attack (AOAs) ranging from approximately 0° to 12°. The numerical simulation is carried out by employing the SST k–ω turbulence model through the Ansys Fluent, and the effects of the riblets’ length and height on aerodynamic performance and flow characteristics of the airfoil are investigated. The results indicate that the amount of drag reduction varies greatly with riblet length and height and the AOA of airfoil flow. By contrast, the riblets are detrimental to the airfoil in some cases. The most effective riblet length is found to be a length of 0.8 chord, which increases the lift and reduces the drag under whole AOA conditions, and the maximum improvements in both are 17.46% and 15.04%, respectively. The most effective height for the riblet with the length of 0.5 chord is 0.6 mm. This also improves the aerodynamic performance and achieves a change rate of 12.67% and 14.8% in the lift and drag coefficients, respectively. In addition, the riblets facilitate a greater improvement in airfoil at larger AOAs. The flow fields demonstrate that the riblets with a drag reduction effect form “the antifriction-bearing” structure near the airfoil surface and effectively restrain the trailing separation vortex. The ultimate cause of the riblet drag reduction effect is the velocity gradient at the bottom of the boundary layers being increased by the riblets, which results in a decrease in boundary thickness and energy loss.

scholarly journals Numerical Investigation on Aerodynamic Performance of Bird’s Airfoils

2020 ◽  
Author(s):  
Ashraf Omar ◽  
Rania Rahuma ◽  
Abdulhaq Emhemmed
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Angle Of Attack ◽  
Aerodynamic Performance ◽  
Airfoil Surface ◽  
Aerodynamic Efficiency ◽  
Gliding Flight ◽  
Surface Permeability ◽  
Low Reynolds ◽  
Better Than

In this work, the aerodynamic performance of four types of bird’s airfoils (eagle, stork, hawk, and albatross) at low Reynolds number and a range of angles of attack during fixed (unflapping) gliding flight was numerically investigated utilizing open-source computational fluid dynamics (CFD) code Stanford University unstructured (SU2) and K-ω Shear Stress Transport (K-ω SST) turbulence model. The flow of the simulated cases was assumed to be incompressible, viscous, and steady. For verification and comparison, a low Reynolds number man-made Eppler 193’s airfoil was simulated. The results revealed that stork has the greatest aerodynamic efficiency followed by albatross and eagle. However, at zero angle of attack, the albatross aerodynamic efficiency exceeded all the other birds by a significant amount. In terms of aerodynamics efficiency, stork’s and albatross’s airfoils performed better than Eppler 193 at angles of attack less than 8°, while at a higher angle of attack all studied birds’ airfoils performed better than Eppler 193. The effect of surface permeability was also investigated for the eagle’s airfoil where the permeable surface occupied one-third of the total airfoil surface. Permeability increased the generated lift and the aerodynamic efficiency of the eagle’s airfoil for angles of attack less than 10°. The increase reached 58% for the lift at zero angle of attack. After the specified angle, the permeability had an adverse effect on the flow which may be due to the transition to turbulent ahead of the permeable section.

Effect of Surface Roughness on Aerodynamic Performance of Turbine Rear Structure

2019 ◽  
Author(s):  
Srikanth Deshpande ◽  
Isak Jonsson ◽  
Valery Chernoray
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Reynolds Number ◽  
Numerical Analysis ◽  
Numerical Simulations ◽  
Numerical Study ◽  
Aerodynamic Performance ◽  
Axial Thrust ◽  
Low Pressure Turbine ◽  
Effect Of Surface

Abstract A turbine rear structure (TRS) is typically used to deswirl the flow from the low pressure turbine (LPT) and hence maximize the axial thrust. It is important to study the effect of surface roughness on aerodynamic performance of TRS. Numerical simulations with surface roughness are performed and results are compared with the data from experiments. Comparisons show that the trends between the numerical analysis and the experiments are in line with one another. Further understanding of numerical analysis shows that, at higher Reynolds number, the effect of surface roughness is more significant when compared to the effects at low-Reynolds number. An attempt has been made to study the transition behavior in the presence of surface roughness. Since boundary layer measurements are planned for the rig, this numerical study provides good inputs in order to plan instrumentation.

Fluid Structure Interaction Simulation on the Bionic Airfoil of the Small Unmanned Plane

2013 ◽  
Vol 387 ◽  
pp. 241-245
Author(s):  
Zeng Qiang Qiao ◽  
Yong Bo Yang
Keyword(s):  
Reynolds Number ◽  
Computational Result ◽  
Fluid Structure Interaction ◽  
Aerodynamic Performance ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Interaction Simulation ◽  
Low Reynolds ◽  
Bionic Airfoil

The quality and dependability of the small unmanned plane is more and more important currently. For the small unmanned plane under the conditions of Low-Reynolds, the air viscosity has relatively greater influence on its aerodynamic performance. This is one of the greatest difficulties to design a small unmanned plane. The aerodynamic performance of bionic aerofoil and NACA 4412 is contrastively analyzed while the Reynolds-Number is and by the Fluent. The computational result and the analysis show that the fluid-structure interaction is an important issue to consider while designing the small unmanned plane.

scholarly journals Numerical Study of Flow Field and Aerodynamic Performance of Straight Bladed VAWT at Variable Tip Speed Ratios

2015 ◽  
Vol 9 (1) ◽  
pp. 1017-1024 ◽  
Author(s):  
Mei Yi ◽  
Qu Jianjun
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Vortex Shedding ◽  
Numerical Study ◽  
Aerodynamic Performance ◽  
Wake Flow ◽  
Speed Ratio ◽  
Power Performance ◽  
Tip Speed Ratio ◽  
And Diffusion

This paper studies the relationship between unsteady flow features and instantaneous torque and power performance of straight bladed vertical axis wind turbine at variable tip speed ratios. The rotor unsteady flow field simulation was carried out by using computational fluid dynamics method. The flow physics and the principle of changing flow field acting on torque performance and power performance have been analyzed where the rotating rotor was the major concern. The results show that the flow feature alters from periodical blade dynamic stall vortexes generation, development and shedding at low tip speed ratio to cyclical formation, evolution and diffusion of blade wake flow with the rising tip speed ratio. Both vortex shedding around the blade and interaction of blade wakes degrade the rotor aerodynamic performance. It is suggested that, to absorb maximum wind energy, delay the blade vortex shedding and reduce the range of blade wake, evolution and diffusion should be included in the rotor aerodynamic design.

A Numerical Study on the Aeroacoustic of a Vaned Centrifugal Fan

2005 ◽  
Author(s):  
S. Khelladi ◽  
S. Kouidri ◽  
F. Bakir ◽  
R. Rey
Keyword(s):  
Unsteady Flow ◽  
High Speed ◽  
Numerical Study ◽  
Noise Generation ◽  
Centrifugal Fan ◽  
Home Appliances ◽  
Centrifugal Fans ◽  
Radial Forces ◽  
Return Channel ◽  
Dipole Sources

High speed vaned centrifugal fans are widely used in several manufacturing and home appliances. For the designers the noise generated by these machines is one of the most important parameters to be reduced. The centrifugal fan used for this study is made up of an impeller, a diffuser and a return channel. The impeller turns at a relatively high speed about 35000 rpm. The objective of this study is to understand the mechanism of the noise generation within this type of machines. The contribution of the tangential and radial forces is highlighted. These fluctuating forces are due to the unsteady flow at the impeller-diffuser interface. The obtained result shows the effect of monopole and dipole sources on the overall noise.

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