Wyniki wyszukiwania - BazTech

1

Lengthwise finning surface as the method of influence on the flow separation in diffusers

Zaryankin A., Rogalev A., Lisin E., Khudyakova V.

Journal of Applied Mathematics and Computational Mechanics

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2017

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Vol. 16, nr 1

127--138

EN

The paper deals with the analysis of power factors acting within the boundary layer for different types of flow: convergent, gradientless and diffuser. Based on the considered formation mechanism of boundary layer separation, a hypothesis about the possible influence on structure and character of a separated flow by changing the gradient of the tangential stresses in the boundary layer was proposed. This impact is proposed to realize by means of the longitudinal finning of diffuser. Verification of the concept is performed on the basis of numerical flow investigation and available experimental data.

2

CFD analysis of aerofoil using dimples and prevent radar signals using stealth technology

Maheswaran R., Manikandan R.

Archives of Materials Science and Engineering

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2016

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Vol. 77, nr 2

72--77

EN

Purpose: The main objective of aircraft aerodynamics is to enhance the aerodynamic characteristics and maneuverability of the aircraft. This enhancement includes the reduction in drag and stall phenomenon. The airfoil which contains dimples will have comparatively less drag than the plain airfoil. Introducing dimples on the aircraft wing will create turbulence by creating vortices which delays the boundary layer separation resulting in decrease of pressure drag and also increase in the angle of stall. In addition, wake reduction leads to reduction in acoustic emission. The overall objective of this paper is to improve the aircraft maneuverability by delaying the flow separation point at stall and thereby reducing the drag by applying the dimple effect over the aircraft wing. Design/methodology/approach: This project includes computational analysis of dimple effect on aircraft wing, using NACA 0018 airfoil. Dimple shapes are circular which locates the inward, outward are selected for the analysis; airfoil is tested under the inlet velocity of 30m/s at different angle of attack (-5°, 0°, 5°, 10°, and 15°). Findings: This analysis favors the dimple effect by increasing L/D ratio and thereby providing the maximum aerodynamic efficiency, which provides the enhanced performance for the aircraft. Practical implications: Stealth technology is based on the principle of reflection and absorption that makes the objects’ observability lower and stealthy. A 'stealth' vehicle will generally have been designed from the motive to reduce RCS (Radar Cross Section) of aircrafts i.e. radar signature of aircrafts.

3

Protodiastole and vessel damage in atherosclerosis

Beraia M., Todua F., Khomeriki I.

Biocybernetics and Biomedical Engineering

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2006

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Vol. 26, no. 3

65-75

EN

Hemodynamic forces are now known to be the localizing factors in atherogenesis, but conclusions as to the causes of the vessel wall damage are inconsistent. The purpose of the study was examination of the blood flow features in the aortic arch and establishment of the initial factors of atherogenesis. 15 men (age from 27 to 35 years) have been examined by magnetic resonance angiography on Siemens-Sonata-Cardio unit. Blood flow peak systolic velocity changes at the opposite walls of the aortic arch have been revealed. During protodiastole, the flow was found to form opposite directed streams, and a flow arrest with a flat flow profile was noted in discrete sites of the aorta. At these specified places, the peak systolic velocity was found to be low. Blood protodiastolic acceleration was 6 times higher than in the systole, and the shear stress was found to exceed the verge of the endothelial endurance. The circular blood flow at the aortic arch in protodiastole is characterized by a high acceleration, and the gradient pressure in the flat profile can damage the internal layers of the vessel.

4

Streamwise vortices induced by semi-circular rods submerged in turbulent boundary layer.

Szumowski A., Wojciechowski J.

Archive of Mechanical Engineering

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2005

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Vol. LII, nr 4

353-360

EN

Two semi-circular rods set up in V-shape form were used to generate streamwise vortices in a turbulent boundary layer. The vortices, due to induced helical flow, supplement the streamwise momentum of retarded air particles at the body surface with the momentum of the external flow. In this experimental study it was found that vortices are at their most intensity if the Reynolds number of the flow over generator, based on the diameter of rods is within the range 10 to the 4 - 1.5 x 10 to the 4. Several semi-circular rods set up in a tooth line were examined in delaying the separation of the turbulent boundary layer at a convex cylindrical surface. It has been noted that delay of separation is at its most efficient when the height of the generator is equal to at least half of the boundary layer thickness.

PL

Wiry, których oś wirowania pokrywa się z głównym kierunkiem przepływu (wiry wzdłużne) powodują ruch śrubowy elementów płynu. Tym samym, jeżeli wiry te generowane są w warstwie przyściennej, powodują intensyfikację transportu pędu w kierunku ścianki, a przez to uzupełnianie strat pędu warstwy przyściennej i opóźnianie jej oderwania. W pracy badano na drodze eksperymentalnej wiry wzdłużne generowane przez pręty półwalcowe zestawione w kształcie litery V, umieszczone na płaskiej ściance. Stwierdzono, że intensywność wirów jest największa dla liczb Reynoldsa w zakresie 10 do potęgi czwartej - 1.5 x 10 do potęgi czwartej i kąta rozwarcia między prętami ok. 60 stopni. Efekt działania wytworzonych w ten sposób wirów na opóźnienie oderwania warstwy przyściennej badano przy opływie wypukłej powierzchni walcowej. Uzykane wyniki świadczą, że skuteczność generatora wirów rośnie ze zwiększeniem promienia półwalca aż do wartości tego promienia równego w przybliżeniu połowie grubości warstwy. Dalsze zwiększenie promienia nie powoduje istotnego wzrostu opóźnienia oderwania.