DESIGN OF LOW-DRAG AUTONOMOUS UNDERWATER VEHICLES AND FLOW CONTROL

2021 ◽  
Vol 158 (A1) ◽  
Author(s):  
E Amromin
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Autonomous Underwater Vehicles ◽  
Reynolds Numbers ◽  
Underwater Vehicles ◽  
Pressure Gradients ◽  
Boundary Layer Suction ◽  
Turbulent Transition ◽  
Blunt Bodies ◽  
Body Shapes

Design of autonomous underwater vehicles (AUV) met the opposite challenges. Their achievable route can be enhanced with drag reduction due to an increase of AUV slenderness. However, blunt short AUV have others operational advantages. The possibility to design low-drag bodies for Reynolds numbers employed by contemporary AUV (2×106<Re<107) is based on a combination of known facts. First, blunt bodies experience a drag crisis associated with laminar-turbulent transition in their boundary layers and some boundary layer suction additionally reduces their drag. Second, the transition can be delayed till much higher Re for bodies without adverse pressure gradients over their forward and medium parts. Suction on sterns of such bodies allows for the very substantial drag reduction. Several body shapes with distributed suction with extremely low slenderness (L/B<1.5) are presented. Their drag coefficients are between 0.007 and 0.02, whereas for ellipsoid of the same slenderness it exceeds 0.08.

scholarly journals The influence of moderate angle-of-attack variation on disturbances evolution and transition to turbulence in supersonic boundary layer on swept wing

2019 ◽  
Vol 234 (1) ◽  
pp. 96-101
Author(s):  
Alexander Kosinov ◽  
Nikolai Semionov ◽  
Yury Yermolaev ◽  
Boris Smorodsky ◽  
Gleb Kolosov ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Theoretical Study ◽  
Angle Of Attack ◽  
Reynolds Numbers ◽  
Supersonic Boundary Layer ◽  
Linear Stability Theory ◽  
Transition To Turbulence ◽  
Computational Results ◽  
Swept Wing ◽  
Turbulent Transition

The paper is devoted to an experimental and theoretical study of effect of moderate angle-of-attack variation on disturbances evolution and laminar-turbulent transition in a supersonic boundary layer on swept wing at Mach 2. Monotonous growth of the transition Reynolds numbers with angle of attack increasing from −2° to 2.7° is confirmed. For the same conditions, calculations based on linear stability theory are performed. The experimental and computational results show a favourable comparison.

Boundary-Layer Control as a Means of Reducing Drag on Fully Submerged Bodies of Revolution

1985 ◽  
Vol 107 (3) ◽  
pp. 342-347 ◽  
Author(s):  
B. Bar-Haim ◽  
D. Weihs
Keyword(s):  
Boundary Layer ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Boundary Layer Control ◽  
Layer Transition ◽  
Bodies Of Revolution ◽  
Boundary Layer Suction ◽  
Technique Optimization ◽  
Axisymmetric Bodies ◽  
Layer Control

The drag of axisymmetric bodies can be reduced by boundary-layer suction, which delays transition and can control separation. In this study, boundary-layer transition is delayed by applying a distributed suction technique. Optimization calculations were performed to define the minimal drag bodies at Reynolds numbers of 107 and 108. The saving in drag relative to optimal bodies with non-controlled boundary layers is shown to be 18 and 78 percent, at Reynolds numbers of 107 and 108, respectively.

Measurements of the Effects of Freestream Turbulence on Separation-Bubble Transition

2002 ◽  
Author(s):  
M. I. Yaras
Keyword(s):  
Pressure Distribution ◽  
Separation Bubble ◽  
Reynolds Numbers ◽  
Pressure Gradients ◽  
Freestream Turbulence ◽  
Test Plate ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition ◽  
Boundary Layer Development ◽  
Layer Development

In this paper, measurements are presented on the effects of freestream turbulence on laminar-to-turbulent transition in separation bubbles, and correlations are proposed for the locations of transition and reattachment on the basis of this data. The boundary layer development is measured on a smooth, flat plate upon which streamwise pressure gradients are imposed by a flexible, contoured wall opposite to the test plate. Two variations in the streamwise pressure distribution are investigated, and two Reynolds numbers are considered for each pressure-gradient setting. For each combination of pressure distribution and Reynolds number, the freestream turbulence intensity and length scale are adjusted systematically by varying the open-area-ratio and cell size of the grid installed at the test-section inlet. Measured quantities consist of velocity obtained with a single-hot wire probe and surface pressures measured through pressure taps.

Mechanism of drag reduction by a surface trip wire on a sphere

2011 ◽  
Vol 672 ◽  
pp. 411-427 ◽  
Author(s):  
KWANGMIN SON ◽  
JIN CHOI ◽  
WOO-PYUNG JEON ◽  
HAECHEON CHOI
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Separation Bubble ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Transition To Turbulence ◽  
Stream Velocity ◽  
Sphere Diameter ◽  
Sphere Surface ◽  
Streamwise Location

The effect of a surface trip wire on the flow around a sphere is experimentally investigated at subcritical Reynolds numbers of Re = 0.5 × 105 – 2.8 × 105 based on the free-stream velocity U∞ and sphere diameter d. By varying the streamwise location (20° – 70° from the stagnation point) and diameter (0.33 × 10−2 < k/d < 1.33 × 10−2) of a trip wire, we measure the drag, surface pressure distribution and boundary layer velocity profiles above the sphere surface, and conduct flow visualization. Depending on the size and streamwise location of the trip wire, three different flow characteristics are observed above the sphere surface. For low Reynolds numbers, the disturbance induced by the trip wire decays downstream and main separation occurs at a streamwise location similar to that of a smooth sphere. As the Reynolds number is increased, laminar separation is delayed farther downstream by the disturbance from the trip wire and the transition to turbulence occurs along the separated shear layer, resulting in the flow reattachment to the sphere surface and thus forming a secondary separation bubble on the sphere surface. Then, the main separation is delayed due to high momentum near the surface and the drag is significantly reduced. When the trip wire produces even larger disturbances through the separation and reattachment right at the trip-wire location for higher Reynolds numbers, the boundary layer flow becomes turbulent soon after the trip-wire location and the main separation is delayed, resulting in drag reduction.

An experimental study of edge effects on rotating-disk transition

2013 ◽  
Vol 716 ◽  
pp. 638-657 ◽  
Author(s):  
Shintaro Imayama ◽  
P. Henrik Alfredsson ◽  
R. J. Lingwood
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Boundary Layer Flow ◽  
Rotating Disk ◽  
Reynolds Numbers ◽  
Absolute Instability ◽  
Global Instability ◽  
Global Mode ◽  
Turbulent Transition ◽  
Layer Flow

AbstractThe onset of transition for the rotating-disk flow was identified by Lingwood (J. Fluid. Mech., vol. 299, 1995, pp. 17–33) as being highly reproducible, which motivated her to look for absolute instability of the boundary-layer flow; the flow was found to be locally absolutely unstable above a Reynolds number of 507. Global instability, if associated with laminar–turbulent transition, implies that the onset of transition should be highly repeatable across different experimental facilities. While it has previously been shown that local absolute instability does not necessarily lead to linear global instability: Healey (J. Fluid. Mech., vol. 663, 2010, pp. 148–159) has shown, using the linearized complex Ginzburg–Landau equation, that if the finite nature of the flow domain is accounted for, then local absolute instability can give rise to linear global instability and lead directly to a nonlinear global mode. Healey (J. Fluid. Mech., vol. 663, 2010, pp. 148–159) also showed that there is a weak stabilizing effect as the steep front to the nonlinear global mode approaches the edge of the disk, and suggested that this might explain some reports of slightly higher transition Reynolds numbers, when located close to the edge. Here we look closely at the effects the edge of the disk have on laminar–turbulent transition of the rotating-disk boundary-layer flow. We present data for three different edge configurations and various edge Reynolds numbers, which show no obvious variation in the transition Reynolds number due to proximity to the edge of the disk. These data, together with the application (as far as possible) of a consistent definition for the onset of transition to others’ results, reduce the already relatively small scatter in reported transition Reynolds numbers, suggesting even greater reproducibility than previously thought for ‘clean’ disk experiments. The present results suggest that the finite nature of the disk, present in all real experiments, may indeed, as Healey (J. Fluid. Mech., vol. 663, 2010, pp. 148–159) suggests, lead to linear global instability as a first step in the onset of transition but we have not been able to verify a correlation between the transition Reynolds number and edge Reynolds number.

scholarly journals Метод учета масштабного эффекта для гидродинамических профилей

2020 ◽  
Author(s):  
A.Yu. Yakovlev ◽  
T. Zin
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Scale Effect ◽  
Reynolds Numbers ◽  
Laminar Separation ◽  
Ship Hulls ◽  
Turbulent Transition ◽  
Calculation Results ◽  
Scaling Parameters ◽  
Profile Characteristics

Учет масштабного эффекта имеет важное значение для задач проектирования судов и их движителей. Сложные формы корпусов судов и современных движителей могут быть представлены в виде комбинации простых базовых элементов, одним из которых является гидродинамический профиль. В работе представлен метод учета масштабного эффекта для плоского гидродинамического профиля. Метод учета основан на численной оценке характеристик профиля с помощью методов идеальной жидкости и расчета пограничного слоя. В методе моделируются эффекты ламинарно-турбулентного перехода и отрыва пограничного слоя, учитывается возможность турбулизации и присоединения пограничного слоя в случае его ламинарного отрыва. Моделирование масштабного эффекта осуществляется путем выбора значений ряда параметров масштабирования из условия согласования расчета с модельными экспериментальными данными, специальной аппроксимации невязки между ними по методу наименьших квадратов и последующего расчета на большие натурные числа Рейнольдса. Показаны особенности влияния параметров масштабирования на характеристики профиля. Эффективность разработанного метода подтверждена сопоставлением с экспериментальными данными.aking into account the scale effect is important for the design of ships and its propulsors. Complex shapes of ship hulls and modern propulsors may be represented as a combination of simple basic elements. The hydrodynamic profile is one of its. This paper presents a method of accounting for the scale effect for the special case of a plane aerodynamic profile. The method of accounting is based on the numerical evaluation of the profile characteristics using the methods of ideal fluid and boundary layer calculation. The method simulates the effects of laminar-turbulent transition and separation of the boundary layer. The possibility of turbulization and joining of the boundary layer in the case of its laminar separation is taken into account. Modeling of the scale effect is carried out by selecting the values of a few scaling parameters. The values are determined from the achievement of convergence the calculation results and the model experimental data. The features of the influence of scaling parameters on the profile characteristics are shown. The next steps of scaling are special least squares approximation of the residuals between calculation results and experimental data and calculation of the hydrofoil characteristics at large full-scale Reynolds numbers. The effectiveness of the developed method is confirmed by comparison with experimental data

Experimental study of laminar-turbulent transition on a swept wing with local boundary-layer suction at subsonic velocities

1998 ◽  
Vol 33 (4) ◽  
pp. 519-525
Author(s):  
V. F. Babuev ◽  
V. I. Biryukov ◽  
V. D. Bokser ◽  
A. F. Kiselev ◽  
V. G. Mikeladze ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Experimental Study ◽  
Swept Wing ◽  
Local Boundary ◽  
Boundary Layer Suction ◽  
Turbulent Transition ◽  
Laminar Turbulent Transition
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