Investigation on the effect of leading edge tubercles of sweptback wing at low reynolds number

2020 ◽  
Vol 21 (6) ◽  
pp. 621
Author(s):  
Veerapathiran Thangaraj Gopinathan ◽  
John Bruce Ralphin Rose ◽  
Mohanram Surya
Keyword(s):  
Leading Edge ◽  
Reynolds Numbers ◽  
Sweep Angle ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Flow Energy ◽  
Airplane Wing ◽  
Low Reynolds ◽  
Naca 0015 ◽  
Wing Performance

Aerodynamic efficiency of an airplane wing can be improved either by increasing its lift generation tendency or by reducing the drag. Recently, Bio-inspired designs have been received greater attention for the geometric modifications of airplane wings. One of the bio-inspired designs contains sinusoidal Humpback Whale (HW) tubercles, i.e., protuberances exist at the wing leading edge (LE). The tubercles have excellent flow control characteristics at low Reynolds numbers. The present work describes about the effect of tubercles on swept back wing performance at various Angle of Attack (AoA). NACA 0015 and NACA 4415 airfoils are used for swept back wing design with sweep angle about 30°. The modified wings (HUMP 0015 A, HUMP 0015 B, HUMP 4415 A, HUMP 4415 B) are designed with two amplitude to wavelength ratios (η) of 0.1 & 0.24 for the performance analysis. It is a novel effort to analyze the tubercle vortices along the span that induce additional flow energy especially, behind the tubercles peak and trough region. Subsequently, Co-efficient of Lift (CL), Co-efficient of Drag (CD) and boundary layer pressure gradients also predicted for modified and baseline (smooth LE) models in the pre & post-stall regimes. It was observed that the tubercles increase the performance of swept back wings by the enhanced CL/CD ratio in the pre-stall AoA region. Interestingly, the flow separation region behind the centerline of tubercles and formation of Laminar Separation Bubbles (LSB) were asymmetric because of the sweep.

Occurrence of Bubbles in a Thin Wire at Low Reynolds Number

1992 ◽  
Vol 114 (2) ◽  
pp. 255-260 ◽  
Author(s):  
K. Sato
Keyword(s):  
Separation Zone ◽  
Reynolds Numbers ◽  
Cavitation Number ◽  
The Other ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Thin Wires ◽  
Different Types ◽  
Low Reynolds ◽  
Air Diffusion

Thin wires of various diameters from 0.07 to 0.7 mm are examined about appearances and characteristics of bubble occurrence behind them in the range of low Reynolds numbers. The appearance of bubbles is very dependent on diameters of wires. Two different types of bubbles can be observed in the present experiment. One is a streamer-type bubble for smaller wires and the other is a small unspherical bubble for larger wires. The incipient and the desinent values of cavitation number also change greatly with the bubble types. The streamer-type bubble is related to the presence of laminar separation zone and the growth due to air diffusion. The small unspherical bubble can be mainly attributed to the motion of rolled-up vortices and the growth due to vaporization.

scholarly journals Force and flowfield measurements to understand unsteady aerodynamics of cycloidal rotors in hover at ultra-low Reynolds numbers

2019 ◽  
Vol 11 ◽  
pp. 175682931983367
Author(s):  
Carolyn M Reed ◽  
David A Coleman ◽  
Moble Benedict
Keyword(s):  
Separation Bubble ◽  
Fluid Dynamic ◽  
Unsteady Aerodynamics ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Dynamic Stall ◽  
Static Case ◽  
Low Reynolds Numbers ◽  
Curvature Effects ◽  
Low Reynolds

This paper provides a fundamental understanding of the unsteady fluid-dynamic phenomena on a cycloidal rotor blade operating at ultra-low Reynolds numbers (Re ∼ 18,000) by utilizing a combination of instantaneous blade force and flowfield measurements. The dynamic blade force coefficients were almost double the static ones, indicating the role of dynamic stall. For the dynamic case, the blade lift monotonically increased up to ±45° pitch amplitude; however, for the static case, the flow separated from the leading edge after around 15° with a large laminar separation bubble. There was significant asymmetry in the lift and drag coefficients between the upper and lower halves of the trajectory due to the flow curvature effects (virtual camber). The particle image velocimetry measured flowfield showed the dynamic stall process during the upper half to be significantly different from the lower half because of the reversal of dynamic virtual camber. Even at such low Reynolds numbers, the pressure forces, as opposed to viscous forces, were found to be dominant on the cyclorotor blade. The power required for rotation (rather than pitching power) dominated the total blade power.

Actuated Transition in an LP Turbine Laminar Separation: An Experimental Approach

2011 ◽  
Author(s):  
Jenny Baumann ◽  
Ulrich Rist ◽  
Martin Rose ◽  
Tobias Ries ◽  
Stephan Staudacher
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Turbine Blades ◽  
Reynolds Numbers ◽  
Experimental Investigations ◽  
Stream Velocity ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Low Reynolds ◽  
Lp Turbine

The reduction of blade counts in the LP turbine is one possibility to cut down weight and therewith costs. At low Reynolds numbers the suction side laminar boundary layer of high lift LP turbine blades tends to separate and hence cause losses in turbine performance. To limit these losses, the control of laminar separation bubbles has been the subject of many studies in recent years. A project is underway at the University of Stuttgart that aims to suppress laminar separation at low Reynolds numbers (60,000) by means of actuated transition. In an experiment a separating flow is influenced by disturbances, small in amplitude and of a certain frequency, which are introduced upstream of the separation point. Small existing disturbances are therewith amplified, leading to earlier transition and a more stable boundary layer. The separation bubble thus gets smaller without need of a high air mass flow as for steady blowing or pulsed vortex generating jets. Frequency and amplitude are the parameters of actuation. The non-dimensional actuation frequency is varied from 0.2 to 0.5, whereas the normalized amplitude is altered between 5, 10 and 25% of the free stream velocity. Experimental investigations are made by means of PIV and hot wire measurements. Disturbed flow fields will be compared to an undisturbed one. The effectiveness of the presented boundary layer control will be compared to those of conventional ones. Phase-logged data will give an impression of the physical processes in the actuated flow.

Research of the suction flow control on wings at low Reynolds numbers

2017 ◽  
Vol 232 (8) ◽  
pp. 1515-1528 ◽  
Author(s):  
Dongli Ma ◽  
Guanxiong Li ◽  
Muqing Yang ◽  
Shaoqi Wang
Keyword(s):  
Flow Control ◽  
Aerodynamic Force ◽  
Separation Bubble ◽  
Reynolds Numbers ◽  
Aerodynamic Characteristics ◽  
Flow State ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Low Reynolds ◽  
Suction Flow

Laminar separation and transition have significant effects on aerodynamic characteristics of the wing under the condition of low Reynolds numbers. Using the flow control methods to delay and eliminate laminar separation has great significance. This study uses the method combined with water tunnel test and numerical calculation to research the effects of suction flow control on the flow state and aerodynamic force of the wing at low Reynolds numbers. The effects of suction flow rate and suction location on laminar separation, transition and aerodynamic performance of the wing are further researched. The results of the research show that, the suction can control laminar separation and transition effectively, when the suction holes are in the interior of the separation bubble, and close to the separation point, the suction has the best control effect. When the Reynolds number is Re = 3.0 × 105, the suction flow control can make the lift-to-drag ratio of the wing increase by 8.62%, and the aerodynamic characteristics of the wing are improved effectively.

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