Shape Of Protuberance Research Articles

Experimental study of cavitating flows of protuberance on the surface of underwater vehicle

The high-speed movement of the underwater vehicle causes cavitation in the flow field. For the underwater vehicle with protuberances on the surface, the geometric shape of the protuberance is bound to affect the local flow field of the underwater vehicle. Furthermore, it affects the generation, development and shedding of cavitation around the vehicle. In order to explore the influence of the geometric shape of the protuberance on the generation and development of the cavitation phenomenon, the experimental and high speed imaging technology are carried out to study the cavitation characteristics of the protuberance on the surface of the underwater vehicle. The results show that with the continuous decrease of vertical motion pressure, the cavitation number decreases gradually, the cavitation scale increases continuously and the phenomenon of periodic shedding occurs. Different shapes of protuberances produce different cavitation effects. The increase of protuberance height can restrain the shedding of cavitation bubbles and form larger cavitation bubbles. The shape of the arc-shaped protuberance can inhibit the occurrence of cavitation and produce fewer cavitation bubbles. The size of the cavitation bubbles produced by the bevel-shaped protuberance is larger, but the cavitation bubbles shedding frequency is also higher.

Numerical Investigation of Bionic Rudder With Leading-Edge Protuberances

The duck's webbed feet are observed by using electron microscopy, and observations indicate that the edges of the webbed feet are the shape of protuberances. Therefore, the rudder with leading-edge protuberances is numerically studied in the present investigation. The rudder has a sinusoidal leading-edge profile along the spanwise direction. The hydrodynamic performance of rudder is analyzed under the influence of leading-edge protuberances. The present investigations are carried out at Re = 3.2 × 105 and 8 × 105. In the case of Re = 3.2 × 105, the curves of lift coefficient illustrate that the protuberant leading-edge scarcely affects the lift coefficient of bionic rudder. However, the drag coefficient of the bionic rudder is markedly lower than that of the unmodified rudder. Therefore, the lift-to-drag ratio of the bionic rudder is obviously higher than the unmodified rudder. In another case of Re = 8 × 105, the advantageous behavior of the bionic rudder with leading-edge protuberances is mainly performed in the post-stall regime. The flow mechanism of the significantly increased efficiency by the protuberant leading-edge is explored. It is obvious that the pairs of counter-rotating vortices are presented over the suction surface of bionic rudder, and therefore, the flow is more likely to adhere to the suction surface of bionic rudder.

Analysis of interlocking performances on non-oriented electrical steels

In order to reduce energy loss in motor, applications of high-efficiency non-oriented electrical steel sheets and optimal laminating process are both important elements. The motor core loss deterioration is influenced by a number of factors, such as flux distribution, stress and strain, space harmonics, temperature, and short circuits between lamination. In conventional clamping method, steel sheets are laminated via interlocking or welding in general manner. The measured energy loss by welding was much larger than that by interlocking. Therefore, interlocking is well known and usually employed with benefit of easy conducting. The protuberance shapes affected the fastening strength. Generally, the intensity of rectangular type is stronger than the circular counterparts. However, the circular interlocking has better magnetic characteristics. To clarify the method effectiveness, interlocking performances regarding fastened strength and magnetic deterioration by lamination were investigated. The key parameters of protuberance shape and forming depth were designed. Precisely manufacturing operation was applied to avoid interlocking failure. Magnetic properties largely influenced by clamping method are crucial to minimizing the magnetic deterioration during laminating procedure. Several experiments for various processing conditions were undertaken, and the quantification results showed the rectangular interlocking had better fastened strength but worsened iron loss comparing with the circular arrangement. To acquire the comprehensive mechanical and electrical identities for electrical steel lamination, deliberate producing conditions regarding minimizing the magnetic deterioration should be adopted prudently.

The Influence of Slight Protuberances in a Micro-Tube Reactor on Methane/Moist Air Catalytic Combustion

The combustion characteristics of methane/moist air in micro-tube reactors with different numbers and shapes of inner wall protuberances are investigated in this paper. The micro-reactor with one rectangular protuberance (six different sizes) was studied firstly, and it is shown that reactions near the protuberance are mainly controlled by diffusion, which has little effect on the outlet temperature and methane conversion rate. The formation of cavities and recirculation zones in the vicinity of protuberances leads to a significant increase of the Arrhenius reaction rate of CH4 and gas velocity. Next, among the six different simulated conditions (0–5 rectangular protuberances), the micro-tube reactor with five rectangular protuberances shows the highest methane conversion rate. Finally, the effect of protuberance shape on methane/moist air catalytic combustion is confirmed, and it is found that the protuberance shape has a greater influence on methane conversion rate than the number of protuberances. The methane conversion rate in the micro-tube decreases progressively in the following order: five triangular slight protuberances > five rectangular protuberances > five trapezoidal protuberances > smooth tube. In all tests of methane/moist air combustion conditions, the micro-tube with five triangular protuberances has the peak efficiency and is therefore recommended for high efficiency reactors.

Structural and electric surface characteristics of heavy ion tracks in poly(ethylene terephthalate) and mica

The entry of high-energy Kr, Xe, and Bi ions into the surface of poly(ethylene terephthalate) (PET) and mica has been imaged. It has been shown that the track images have the shape of protuberances in both cases. The formation of protuberances is associated with the degradation of the material in the track region, in the formation of an amorphous structure, and the release of low-molecular radiolysis products as gaseous compounds. Holding the irradiated PET samples in water and dilute alkaline solution for several hours changes the surface topography due to hydrolysis of the material and escape of the radiolysis products to the solution. The kinetics of track etching in the dilute alkaline solution and pore formation have been studied. The electrical resistance and the permeability of the tracks in KCl, LiCl, MgCl2, and BaCl2 electrolytes have been measured.

Simple colloidal lithography method to fabricate large-area moth-eye antireflective structures on Si, Ge, and GaAs for IR applications

A two-step colloidal lithography process (Langmuir–Blodgett dip coating + reactive ion etching) was developed to fabricate single and double-sided moth-eye structures in Si, Ge, and GaAs for antireflection applications in the IR. Large increases in transmittance were obtained in all three material platforms (up to 97% single-side and 91% absolute transmittance) over the λ = 4−20+ μm region. Effective medium theory and the transfer matrix method were used to predict IR optical response of moth-eye substrates as well as investigate the effect of protuberance shape on antireflectance behavior. Overall, it is demonstrated that colloidal lithography and etching provide an easy and generic way to synthesize moth-eyes in different IR material platforms.

Sealing components of sowing device of overpressure

Design and operational principles of pneumatic sowing device of overpressure with sealing of seed chamber are described. Process of seed placement into transport channel is researched theoretically. Conditions of secured pushing out of superfluous seeds without jamming and damages are determined. Shape of protuberances of seeding plate is specified.

Aerodynamics Characteristic of Axisymmetric Surface Protuberance in Supersonic Regime

The present work deals with the problem of an axi-symmetric surface protuberance mounted on a spherical nosed body of revolution. The numerical computations are carried out for laminar supersonic viscous flow for trapezoidal shape axi-symmetric protuberances. A free stream Mach number ranging from 3 to 8 in steps of 1 at a fixed free stream Reynolds number of 1.8×104 has been used in the present study. The steady solutions are obtained using a time marching approach. A newly developed Particle Velocity Upwinding (PVU) scheme has been used for the computation. The spatial flow pattern exhibits a strong bow shock in front of the hemispherical nose, which engulfs the entire base body. Near the protuberance, the fluid particle decelerates due to the adverse pressure created by the protuberance and thus the flow separates in front of the protuberance. This point of separation is found to be a function of Mach number and the protuberance shape. A low-pressure expansion region dominates the base region of the obstacle. The reattachment point for the base separation is also a function of Mach number. As the Mach number is increased the reattachment point shifts toward the protuberances base. A weak recompression shock is also seen in the base, which affects the separated zone behind the protuberance. The important design parameters such as skin friction, heat transfer, drag, and surface pressure coefficients are reported extensively.

Molecular identification based on ITS sequences for Kappaphycus and Eucheuma cultivated in China

The systematic classification of the Eucheumatoideae is difficult because of their variable morphology and interpretation of reproductive structures. Kappaphycus and Eucheuma specimens cultivated on the Hainan and Fujian coast of China were introduced from Vietnam, the Philippines and Indonesia. Combined with morphological characteristics, all Kappaphycus and Eucheuma cultivated strains were identified by internal transcribed spacer (ITS) sequences. The phylogenetic tree was constructed using neighbor-joining and maximum likelihood methods. The results indicate that different ITS sequence lengths occurred in the different genera and species. An obvious difference in morphology could be found in the protuberance shape between Kappaphycus and Eucheuma. The protuberance in Eucheuma was thorn-like and in Kappaphycus was wartlike or papillate. Their ITS sequence lengths differed significantly in nucleotide variation rates up to 58.55%–63.90%. All nucleotide variations occurred in the ITS1 and ITS2 regions except for five nucleotide transversions in the 5.8S rDNA region. In addition, the difference was at the branches among congeneric species. Kappaphycus sp. had branches with small buds, while K. alvarezii did not have such a feature. The nucleotide variation rates varied from 7.02% to 7.48% among species; within the same species of the clades it was <1.20%. Eucheumatoideae algae cultivated in China consisted of three clades, K. alvarezii, Kappaphycus sp., and E. denticulatum. The results indicate that ITS sequence analysis was an effective way for identification of interspecies and intraspecies phylogenetic relationships and might provide a clue for molecular identification of algal Eucheumatoideae.

An experimental study of reflected shock wave structure over a wedge with surface roughness.

The detailed wave structure of a reflected shock wave over a wedge with surface roughness is examined. The rough wedge has regular, two-dimensional geometric protuberances. The shape of protuberances was square in cross section and the spacing was the same as its height. The protuberances varied in size from 0.5 to 8 mm. The incident shock Mach number M was 1.4 and wedge angle varied from 20°to 45°. It is found that the geometric wave structure varies as time proceeds and a pseudostationary (self-similar) state is not attained in our experimental conditions. However the wave configurations are similar as long as the numbers of protuberances over which the incident wave traverses are the same. It is also found that there are four types of shock reflection corresponding to transition. They are MR→MR, MR→RR→MR, RR→MR, and RR→RR.

Augmentation of Turbulent Heat Transfer on a Flat Plate with a Three-dimensional Protuberance : 2nd Report, Shape Effect and Row of the Protuberance

In the 1st report, concerning a single finite circular cylinder placed on a flat plate, it was made clear that the three-dimensional reattachment of a blow down flow from upper end of the cylinder and the formation of a pair of longitudinal vorices play an important role in the augmentation of heat transfer. Following this, this report describes the experimental results on the flow structure and local heat transfer characteristics influenced by (I) the change in the shape of protuberance (cube, square cylinder and circular cone) and (II) the mutual interaction of longitudinal vortices produced in a row by row of protuberances.