Small-Scale Atmospheric Turbulence and Its Impact on Laminar-to-Turbulent Transition

ABSTRACTThe drag coefficient and the laminar-to-turbulent transition for the aerofoil component of a wing model are optimised using an adaptive upper surface with two actuation points. The effects of the new shaped aerofoils on the global drag coefficient of the wing model are also studied. The aerofoil was optimised with an ‘in-house’ genetic algorithm program coupled with a cubic spline aerofoil shape reconstruction and XFoil 6.96 open-source aerodynamic solver. The wing model analysis was performed with the open-source solver XFLR5 and the 3D Panel Method was used for the aerodynamic calculation. The results of the aerofoil optimisation indicate improvements of both the drag coefficient and transition delay of 2% to 4%. These improvements in the aerofoil characteristics affect the global drag of the wing model, reducing it by up to 2%. The analyses were conducted for a single Reynolds number and speed over a range of angles of attack. The same cases will also be used in the experimental testing of the manufactured morphing wing model.

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Experimental Analysis of Pressure Drop and Laminar to Turbulent Transition for Gas Flows in Smooth Microtubes

Heat Transfer Engineering ◽

10.1080/01457630701326308 ◽

2007 ◽

Vol 28 (8-9) ◽

pp. 670-679 ◽

Cited By ~ 29

Author(s):

Gian Luca Morini ◽

Marco Lorenzini ◽

Stéphane Colin ◽

Sandrine Geoffroy

Keyword(s):

Pressure Drop ◽

Experimental Analysis ◽

Gas Flows ◽

Laminar To Turbulent Transition ◽

Turbulent Transition

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Detecting Transition in Flat Plate Flow With Laser Interferometric Vibrometry (LIV)

Volume 2A: Turbomachinery ◽

10.1115/gt2016-56043 ◽

2016 ◽

Cited By ~ 1

Author(s):

Pascal Bader ◽

Wolfgang Sanz ◽

Johannes Peterleithner ◽

Jakob Woisetschläger ◽

Franz Heitmeir ◽

...

Keyword(s):

Flat Plate ◽

Measurement Techniques ◽

Transitional Zone ◽

Transport Processes ◽

Transitional Region ◽

Test Cases ◽

Laminar To Turbulent Transition ◽

Turbulent Transition ◽

Measurement Results ◽

Laser Interferometric

Flow in turbomachines is generally highly turbulent. The boundary layers, however, often exhibit laminar-to-turbulent transition. Relaminarization from turbulent to laminar flow may also occur. The state of the boundary layer is important since it strongly influences transport processes like skin friction and heat transfer. It is therefore vitally important for the designer to understand the process of laminar-to-turbulent transition and to determine the position of transition onset and the length of the transitional region. In order to better understand transition and relaminarization it is helpful to study simplified test cases first. Therefore, in this paper the flow along a flat plate is experimentally studied to investigate laminar-to-turbulent transition. Measurements were performed for the different free-stream velocities of 5 m/s and 10 m/s. Several measurement techniques were used in order to reliably detect the transitional zone: the Preston tube, hot wire anemometry, thermography and Laser Interferometric Vibrometry (LIV). The first two measurement techniques are extensively in use at the institute ITTM and by other research groups. They are therefore used as a reference for validating the LIV measurement results. An advantage of the LIV technique is that it does not need any seeding of the fluid and that it is non-intrusive. Therefore this measurement technique does not influence the flow, and it can be used in narrow flow passages since there is no blockage, in contrast to probe-based measurement techniques. Further to the measurements, computational simulations were performed with the Fluent® and CFX® codes from ANSYS®, as well as with the in-house code Linars. The Menter SST k-ω turbulence model with the γ-ReΘ transition model was used in order to test its capability to predict the laminar-to-turbulent transition.

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From Whales to Fans

Mechanical Engineering ◽

10.1115/1.2011-may-1 ◽

2011 ◽

Vol 133 (05) ◽

pp. 24-29 ◽

Cited By ~ 1

Author(s):

Alan S. Brown

Keyword(s):

Technology Use ◽

Humpback Whale ◽

Transition Regime ◽

Tidal Power ◽

Technology Platform ◽

Laminar To Turbulent Transition ◽

Turbulent Transition

This article discusses a story about a man named Fish who noticed something unusual about whale flippers and who, after nearly 30 years, turned it into a technology platform. This technology takes its inspiration from the natural design of the bumps, or tubercles, on humpback whale flippers. The 24-foot-diameter fans, based on tubercle technology, use half the number of blades and move 25% more air and consume 25% less power than fans with conventional blades turning at the same speed. After thousands of years of hiding in plain sight, tubercles are emerging as a real, if limited, technology platform. Research has shown tubercles work only on thick, tapered wings operating in a very narrow laminar-to-turbulent transition regime. Whale-inspired fans are already available, and wind and tidal power blades could be the next.

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