Rod-airfoil interaction noise becomes a major issue in some aeronautical applications.The design of four wavy leading edges(WLEs)with varying wavelengths,bioinspired by the tubercles on humpback whales’flippers,aims ...Rod-airfoil interaction noise becomes a major issue in some aeronautical applications.The design of four wavy leading edges(WLEs)with varying wavelengths,bioinspired by the tubercles on humpback whales’flippers,aims to mitigate far-field noise.Among these cases,a reduction in the wavelength is found to be advantageous for noise suppression,with the smallest wavelength case achieving a maximum noise reduction of 1.9 dB.Furthermore,the noise radiation induced by WLEs is suppressed mainly at medium frequencies.The theory of multiprocess aeroacoustics is applied to reveal their underlying mechanisms.The dominant factor is the source cutoff effect,which significantly decreases the source strength on hills.Additionally,spanwise decoherence with phase interference serves as another crucial mechanism,particularly for reducing mid-frequency noise.展开更多
Microstrip transmission lines connecting to the millimeter wave radar chip and antenna significantly affect the radiation efficiency and bandwidth of the antenna.Here,a wideband non-uniform wavy microstrip line for co...Microstrip transmission lines connecting to the millimeter wave radar chip and antenna significantly affect the radiation efficiency and bandwidth of the antenna.Here,a wideband non-uniform wavy microstrip line for complex impedance in automotive radar frequency range is proposed.Unlike the gradient transmission line,the wavy structure is composed of periodically semi-circular segments.By adjusting the radius of the semi-circular,the surface current is varied and concentrated on the semi-circular segments,allowing a wider tunability range of the resonant frequency.The results reveal that the bandwidth of the loaded wavy transmission line antenna improves to 9.37 GHz,which is 5.81 GHz wider than that of the loaded gradient line.The gain and the half power beam width of the loaded antenna are about 14.69 dB and 9.58°,respectively.The proposed non-uniform microstrip line scheme may open up a route for realizing wideband millimeter-wave automotive radar applications.展开更多
Numerical computation models of air cooling heat transfer and flow behaviors in triangular wavy fin channels(TWFC) were established with structural parameters of fins considered.The air side properties of heat transfe...Numerical computation models of air cooling heat transfer and flow behaviors in triangular wavy fin channels(TWFC) were established with structural parameters of fins considered.The air side properties of heat transfer coefficient and pressure drop are displayed with variable structural parameters of fins and inlet velocities of cooling air.Within the range of simulation,TWFC has the best comprehensive performance when inlet velocity vin=4-10 m/s.Compared with those of straight fins,the simulation results reveal that the triangular wavy fin channels are of higher heat transfer performances especially with the fin structural parameters of fin-height Fh=9.0 mm,fin-pitch Fp=2.5-3.0 mm,fin-wavelength λ=14.0-17.5 mm and fin-wave-amplitude A=1.0-1.2 mm.The correlations of both heat transfer factor and friction factor are presented,and the deviations from the experimental measurements are within 20%.展开更多
On going trend of miniaturization in electronic rel at ed parts, which is an average of two times in every 5～7 years introduce grindin g challenges. In grinding process, the surface waviness control of thin parts is ...On going trend of miniaturization in electronic rel at ed parts, which is an average of two times in every 5～7 years introduce grindin g challenges. In grinding process, the surface waviness control of thin parts is an ardent task due to its warpage, induced by the high specific grinding energy (2～10 J/mm 3). Therefore, coolant is often used to avoid thermal damage, obtai n better surface integrity and to prolong wheel life. However coolant, the incomp ressibility media introduce high forces at the grinding zone creating dimensiona l as well as shape instability. In view of these situations chilled air was ap plied in place of conventional coolant. The chilled air is produced using a two -stage vapor compression refrigeration cycle with characteristics of: temperatu re -35 ℃, pressure 0.2～0.3 MPa and flow rate 0.4 m 3/min. Also traces of eco - oil mist that encompass the chilled air are supplied to the grinding zone. B oth chilled air and eco-oil mist are applied through two independent paths of a specially designed twin compartment nozzle for maximizing the penetration. This paper investigates the grinding characteristics of mold insert which is closer to M2 tool steel (component widely used in connector industries) when using chil led air as coolant media. Grinding experiments were conducted using a vitrified bond CBN wheel (B91N100V) and a surface grinder. Initial study was focussed on establishing the most suita ble clamping method for the thin mold insert. FEM analysis and grinding experime nt studies were performed to quantitatively analyze the clamping induced deflect ion. Waviness value (W t) of (24～62) μm was achieved for resin clampi n g whereas (4～8) μm, (4～6) μm were achieved for magnetic and wax clamping res pe ctively. Wax clamping is predominantly used in all the grinding experiments that characterize the grinding process, which use chilled air as the coolant media. Between 0.15 to 0.9 mm 3/mm.s of specific material removal rate, ground sur face temperature of mold insert was increased from 0.3 ℃ to 59.7 ℃ for chi lled air. For the similar grinding conditions with the coolant fluid an increase from 0.9 ℃ to 14.4 ℃ was recorded. With increase of specific material removal rate from 0.15 to 0.65 mm 3/mm.s, F t/F n ratio was increased from (0.2 to 0.4), (0.6 to 1.67) for wet coolant and chilled air respectively. Despite of high F t/F n ratio and ground surface temperature, chilled air method has shown a surface waviness, W t from (2 to 5.6) μm. Microstructure examination of chilled air produced ground surface was comparable to those of using coolant fluids. Surface finish, R a of (0.45～0.7) μm was achieved for mold insert . This work will enable to have clear understanding about the quantitative influe nce of chilled air as well as the clamping method against the surface waviness o f thin mold insert.展开更多
基金supported by the National Natural Science Foundation of China(12322210,12172351,92252202,and 12388101)the Fundamental Research Funds for the Central Universities.
文摘Rod-airfoil interaction noise becomes a major issue in some aeronautical applications.The design of four wavy leading edges(WLEs)with varying wavelengths,bioinspired by the tubercles on humpback whales’flippers,aims to mitigate far-field noise.Among these cases,a reduction in the wavelength is found to be advantageous for noise suppression,with the smallest wavelength case achieving a maximum noise reduction of 1.9 dB.Furthermore,the noise radiation induced by WLEs is suppressed mainly at medium frequencies.The theory of multiprocess aeroacoustics is applied to reveal their underlying mechanisms.The dominant factor is the source cutoff effect,which significantly decreases the source strength on hills.Additionally,spanwise decoherence with phase interference serves as another crucial mechanism,particularly for reducing mid-frequency noise.
基金Supported by the National Natural Science Foundation of China( 61974104)。
文摘Microstrip transmission lines connecting to the millimeter wave radar chip and antenna significantly affect the radiation efficiency and bandwidth of the antenna.Here,a wideband non-uniform wavy microstrip line for complex impedance in automotive radar frequency range is proposed.Unlike the gradient transmission line,the wavy structure is composed of periodically semi-circular segments.By adjusting the radius of the semi-circular,the surface current is varied and concentrated on the semi-circular segments,allowing a wider tunability range of the resonant frequency.The results reveal that the bandwidth of the loaded wavy transmission line antenna improves to 9.37 GHz,which is 5.81 GHz wider than that of the loaded gradient line.The gain and the half power beam width of the loaded antenna are about 14.69 dB and 9.58°,respectively.The proposed non-uniform microstrip line scheme may open up a route for realizing wideband millimeter-wave automotive radar applications.
基金Project(50976022) supported by the National Natural Science Foundation of ChinaProject(BY2011155) supported by the Provincial Science and Technology Innovation and Transformation of Achievements of Special Fund Project of Jiangsu Province,China
文摘Numerical computation models of air cooling heat transfer and flow behaviors in triangular wavy fin channels(TWFC) were established with structural parameters of fins considered.The air side properties of heat transfer coefficient and pressure drop are displayed with variable structural parameters of fins and inlet velocities of cooling air.Within the range of simulation,TWFC has the best comprehensive performance when inlet velocity vin=4-10 m/s.Compared with those of straight fins,the simulation results reveal that the triangular wavy fin channels are of higher heat transfer performances especially with the fin structural parameters of fin-height Fh=9.0 mm,fin-pitch Fp=2.5-3.0 mm,fin-wavelength λ=14.0-17.5 mm and fin-wave-amplitude A=1.0-1.2 mm.The correlations of both heat transfer factor and friction factor are presented,and the deviations from the experimental measurements are within 20%.
文摘On going trend of miniaturization in electronic rel at ed parts, which is an average of two times in every 5～7 years introduce grindin g challenges. In grinding process, the surface waviness control of thin parts is an ardent task due to its warpage, induced by the high specific grinding energy (2～10 J/mm 3). Therefore, coolant is often used to avoid thermal damage, obtai n better surface integrity and to prolong wheel life. However coolant, the incomp ressibility media introduce high forces at the grinding zone creating dimensiona l as well as shape instability. In view of these situations chilled air was ap plied in place of conventional coolant. The chilled air is produced using a two -stage vapor compression refrigeration cycle with characteristics of: temperatu re -35 ℃, pressure 0.2～0.3 MPa and flow rate 0.4 m 3/min. Also traces of eco - oil mist that encompass the chilled air are supplied to the grinding zone. B oth chilled air and eco-oil mist are applied through two independent paths of a specially designed twin compartment nozzle for maximizing the penetration. This paper investigates the grinding characteristics of mold insert which is closer to M2 tool steel (component widely used in connector industries) when using chil led air as coolant media. Grinding experiments were conducted using a vitrified bond CBN wheel (B91N100V) and a surface grinder. Initial study was focussed on establishing the most suita ble clamping method for the thin mold insert. FEM analysis and grinding experime nt studies were performed to quantitatively analyze the clamping induced deflect ion. Waviness value (W t) of (24～62) μm was achieved for resin clampi n g whereas (4～8) μm, (4～6) μm were achieved for magnetic and wax clamping res pe ctively. Wax clamping is predominantly used in all the grinding experiments that characterize the grinding process, which use chilled air as the coolant media. Between 0.15 to 0.9 mm 3/mm.s of specific material removal rate, ground sur face temperature of mold insert was increased from 0.3 ℃ to 59.7 ℃ for chi lled air. For the similar grinding conditions with the coolant fluid an increase from 0.9 ℃ to 14.4 ℃ was recorded. With increase of specific material removal rate from 0.15 to 0.65 mm 3/mm.s, F t/F n ratio was increased from (0.2 to 0.4), (0.6 to 1.67) for wet coolant and chilled air respectively. Despite of high F t/F n ratio and ground surface temperature, chilled air method has shown a surface waviness, W t from (2 to 5.6) μm. Microstructure examination of chilled air produced ground surface was comparable to those of using coolant fluids. Surface finish, R a of (0.45～0.7) μm was achieved for mold insert . This work will enable to have clear understanding about the quantitative influe nce of chilled air as well as the clamping method against the surface waviness o f thin mold insert.
