scholarly journals Aerodynamic profile drag

2021 ◽  
Author(s):  
Matej Sabo ◽  
◽  
Martin Bugaj
Keyword(s):  
Fluid Dynamics ◽  
Boundary Layer ◽  
European Union ◽  
Laminar Flow ◽  
Friction Drag ◽  
Form Drag ◽  
Basic Principles ◽  
Total Drag ◽  
Laminar Flow Control ◽  
Physical Principles

Higher awareness of aviation sustainability and environmental impact creates more research on profile drag reduction. The basic principles of aerodynamic profile drag are described and its role within the total drag. The boundary layer is defined using mathematical and physical principles of fluid dynamics. There are two types of movement inside the boundary layer: laminar and turbulent. In these, their impact on profile drag is analysed. The profile drag of a wing has two sources: form drag and friction drag. Applications with the most impact, throughout history, on both types of drag reductions were reviewed. Because most of the total drag comes from friction, researchers focus more on it compared to form drag. The significant way of reducing friction drag is postponing the transition of laminar flow into turbulent. The control of laminar flow became crucial for reducing friction drag. In the last two decades, European Union supported multiple projects concerning laminar flow control. These advancements in the field are starting to get implemented and tested on new aircraft by manufactures.

Towards transition modelling for supersonic laminar flow control based on spanwise periodic roughness elements

2005 ◽  
Vol 363 (1830) ◽  
pp. 1079-1096 ◽  
Author(s):  
Meelan Choudhari ◽  
Chau-Lyan Chang ◽  
Li Jiang
Keyword(s):  
Boundary Layer ◽  
Laminar Flow ◽  
Flow Control ◽  
Leading Edge ◽  
Design And Optimization ◽  
Supersonic Aircraft ◽  
Laminar Flow Control ◽  
Key Enabling Technologies ◽  
Novel Concept ◽  
Prediction Approach

Laminar flow control (LFC) is one of the key enabling technologies for quiet and efficient supersonic aircraft. Recent work at Arizona State University (ASU) has led to a novel concept for passive LFC, which employs distributed leading edge roughness to limit the growth of naturally dominant crossflow instabilities in a swept-wing boundary layer. Predicated on nonlinear modification of the mean boundary-layer flow via controlled receptivity, the ASU concept requires a holistic prediction approach that accounts for all major stages within transition in an integrated manner. As a first step in developing an engineering methodology for the design and optimization of roughness-based supersonic LFC, this paper reports on canonical findings related to receptivity plus linear and nonlinear development of stationary crossflow instabilities on a Mach 2.4, 73° swept airfoil with a chord Reynolds number of 16.3 million.

Flow over a glider canopy

2014 ◽  
Vol 118 (1204) ◽  
pp. 669-682
Author(s):  
A. S. Jonker ◽  
J. J. Bosman ◽  
E. H. Mathews ◽  
L. Liebenberg
Keyword(s):  
Fluid Dynamics ◽  
Boundary Layer ◽  
Computational Fluid Dynamics ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Aerodynamic Drag ◽  
Canopy Gap ◽  
Experimental Investigations ◽  
Front Part ◽  
Gap Width

Abstract In order to minimise drag, the front part of most modern glider fuselages is shaped so that laminar flow is preserved to a position close to the wing-to-fuselage junction. Experimental investigations on a full-scale JS1 competition glider however revealed that the laminar boundary layer in fact trips to turbulent flow at the fuselage-to-canopy junction position, increasing drag. This is possibly due to ventilation air leaking from the cockpit to the fuselage surface through the canopy seal, or that the gap is merely too large and therefore trips the boundary layer to turbulent flow. The effect of air leaking from the fuselage-to-canopy gap as well as the size of the gap was thus investigated with the use of computational fluid dynamics. It was found that if air was leaking through this gap the boundary layer would be tripped from laminar to turbulent flow. It was also found that the width of the canopy-to-fuselage gap plays a significant role in the preservation of laminar flow. If the gap is less than 1mm wide, the attached boundary layer is able to negotiate the gap without being tripped to turbulent flow, while if the gap is 3mm and wider, it will be tripped from laminar to turbulent flow. The work shows that aerodynamic drag on a glider can be significantly minimised by completely sealing the fuselage-to-canopy gap and by ensuring a seal gap-width of less than 1mm.

scholarly journals Connecting Flow over Complex Terrain to Hydrodynamic Roughness on a Coral Reef

2018 ◽  
Vol 48 (7) ◽  
pp. 1567-1587 ◽  
Author(s):  
Justin S. Rogers ◽  
Samantha A. Maticka ◽  
Ved Chirayath ◽  
C. Brock Woodson ◽  
Juan J. Alonso ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Coral Reef ◽  
Complex Terrain ◽  
American Samoa ◽  
Relative Depth ◽  
Form Drag ◽  
Simple Method ◽  
Linear Coefficient ◽  
Total Drag ◽  
Extensive Field

AbstractFlow over complex terrain causes stress on the bottom leading to drag, turbulence, and formation of a boundary layer. But despite the importance of the hydrodynamic roughness scale z0 in predicting flows and mixing, little is known about its connection to complex terrain. To address this gap, we conducted extensive field observations of flows and finescale measurements of bathymetry using fluid-lensing techniques over a shallow coral reef on Ofu, American Samoa. We developed a validated centimeter-scale nonhydrostatic hydrodynamic model of the reef, and the results for drag compare well with the observations. The total drag is caused by pressure differences creating form drag and is only a function of relative depth and spatially averaged streamwise slope, consistent with scaling for k–δ-type roughness, where k is the roughness height and δ is the boundary layer thickness. We approximate the complex reef surface as a superposition of wavy bedforms and present a simple method for predicting z0 from the spatial root-mean-square of depth and streamwise slope of the bathymetric surface and a linear coefficient a1, similar to results from other studies on wavy bedforms. While the local velocity profiles vary widely, the horizontal average is consistent with a log-layer approximation. The model grid resolution required to accurately compute the form drag is O(10–50) times the dominant horizontal hydrodynamic scale, which is determined by a peak in the spectra of the streamwise slope. The approach taken in this study is likely applicable to other complex terrains and could be explored for other settings.

scholarly journals Experimental investigation of hybrid laminar flow control by a modular flat plate model in the DNW-NWB

2021 ◽  
Author(s):  
Heinrich Lüdeke ◽  
Christian Breitenstein
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Laminar Flow ◽  
Flow Control ◽  
Flat Plate ◽  
Detailed Examination ◽  
Tunnel Model ◽  
Laminar Flow Control ◽  
Layer Flow ◽  
Numerical Approaches

AbstractTo determine the characteristics of new suction concepts for hybrid laminar flow control (HLFC) a modular flat plate wind tunnel model is investigated in the DNW-NWB wind tunnel facility. This approach allows detailed examination of suction characteristics in consideration of realistic boundary layer flow conditions. The following evaluation reveals the effects of joining methods between successive panels and other surface disturbances of porous materials and underlying chambers on HLFC techniques. After successful measurements with and without suction panels, this paper compares experimental results with theoretical and numerical approaches and draws conclusions from N-factor results and boundary layer (BL) measurements.

The boundary layer of swimming fish

2001 ◽  
Vol 204 (1) ◽  
pp. 81-102 ◽  
Author(s):  
E.J. Anderson ◽  
W.R. McGillis ◽  
M.A. Grosenbaugh
Keyword(s):  
Boundary Layer ◽  
Laminar Flow ◽  
Swimming Performance ◽  
Reynolds Numbers ◽  
Normal Velocity ◽  
Friction Drag ◽  
Law Of The Wall ◽  
Profile Shape ◽  
Mustelus Canis ◽  
Boundary Layer Profile

Tangential and normal velocity profiles of the boundary layer surrounding live swimming fish were determined by digital particle tracking velocimetry, DPTV. Two species were examined: the scup Stenotomus chrysops, a carangiform swimmer, and the smooth dogfish Mustelus canis, an anguilliform swimmer. Measurements were taken at several locations over the surfaces of the fish and throughout complete undulatory cycles of their propulsive motions. The Reynolds number based on length, Re, ranged from 3×10(3) to 3×10(5). In general, boundary layer profiles were found to match known laminar and turbulent profiles including those of Blasius, Falkner and Skan and the law of the wall. In still water, boundary layer profile shape always suggested laminar flow. In flowing water, boundary layer profile shape suggested laminar flow at lower Reynolds numbers and turbulent flow at the highest Reynolds numbers. In some cases, oscillation between laminar and turbulent profile shapes with body phase was observed. Local friction coefficients, boundary layer thickness and fluid velocities at the edge of the boundary layer were suggestive of local oscillatory and mean streamwise acceleration of the boundary layer. The behavior of these variables differed significantly in the boundary layer over a rigid fish. Total skin friction was determined. Swimming fish were found to experience greater friction drag than the same fish stretched straight in the flow. Nevertheless, the power necessary to overcome friction drag was determined to be within previous experimentally measured power outputs. No separation of the boundary layer was observed around swimming fish, suggesting negligible form drag. Inflected boundary layers, suggestive of incipient separation, were observed sporadically, but appeared to be stabilized at later phases of the undulatory cycle. These phenomena may be evidence of hydrodynamic sensing and response towards the optimization of swimming performance.

Status and perspectives of laminar flow

2005 ◽  
Vol 109 (1102) ◽  
pp. 639-644 ◽  
Author(s):  
G. Schrauf
Keyword(s):  
Boundary Layer ◽  
Laminar Flow ◽  
Flow Control ◽  
Boundary Layer Transition ◽  
Technology Readiness ◽  
Layer Transition ◽  
The Status ◽  
Natural Laminar Flow ◽  
Laminar Flow Control

AbstractAfter identifying the ecological and economic drivers for use of laminar flow technology, we outline the mechanisms of laminarturbulent boundary layer transition and review the status of natural laminar flow (NLF) and hybrid laminar flow control (HLFC). New ways to reduce the complexity of HLFC systems are presented, and the remaining steps to achieve technology readiness are discussed.

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