Drag optimisation of a wing equipped with a morphing upper surface

2016 ◽  
Vol 120 (1225) ◽  
pp. 473-493 ◽  
Author(s):  
A. Koreanschi ◽  
O. Sugar-Gabor ◽  
R. M. Botez
Keyword(s):  
Genetic Algorithm ◽  
Reynolds Number ◽  
Drag Coefficient ◽  
Open Source ◽  
Experimental Testing ◽  
Shape Reconstruction ◽  
Laminar To Turbulent Transition ◽  
Wing Model ◽  
Turbulent Transition ◽  
Transition Delay

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.

scholarly journals Laminar-to-turbulent transition of pipe flows through puffs and slugs

2008 ◽  
Vol 614 ◽  
pp. 425-446 ◽  
Author(s):  
MINA NISHI ◽  
BÜLENT ÜNSAL ◽  
FRANZ DURST ◽  
GAUTAM BISWAS
Keyword(s):  
Reynolds Number ◽  
Pipe Flow ◽  
Axial Direction ◽  
Reynolds Numbers ◽  
Turbulent Pipe Flow ◽  
Test Facility ◽  
Pipe Flows ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition ◽  
Slug Flows

Laminar-to-turbulent transition of pipe flows occurs, for sufficiently high Reynolds numbers, in the form of slugs. These are initiated by disturbances in the entrance region of a pipe flow, and grow in length in the axial direction as they move downstream. Sequences of slugs merge at some distance from the pipe inlet to finally form the state of fully developed turbulent pipe flow. This formation process is generally known, but the randomness in time of naturally occurring slug formation does not permit detailed study of slug flows. For this reason, a special test facility was developed and built for detailed investigation of deterministically generated slugs in pipe flows. It is also employed to generate the puff flows at lower Reynolds numbers. The results reveal a high degree of reproducibility with which the triggering device is able to produce puffs. With increasing Reynolds number, ‘puff splitting’ is observed and the split puffs develop into slugs. Thereafter, the laminar-to-turbulent transition occurs in the same way as found for slug flows. The ring-type obstacle height, h, required to trigger fully developed laminar flows to form first slugs or puffs is determined to show its dependence on the Reynolds number, Re = DU/ν (where D is the pipe diameter, U is the mean velocity in the axial direction and ν is the kinematic viscosity of the fluid). When correctly normalized, h+ turns out to be independent of Reτ (where h+ = hUτ/ν, Reτ = DUτ/ν and $U_{\tau}\,{=}\,\sqrt{\tau_{w}/ \rho}$; τw is the wall shear stress and ρ is the density of the fluid).

Characterization of the Ionic Wind Induced by a Sine DBD Actuator Used for Laminar-to-Turbulent Transition Delay

2008 ◽  
Author(s):  
Vincent Boucinha ◽  
Pierre Magnier ◽  
Régine Weber ◽  
Annie Leroy-Chesneau ◽  
BinJie Dong ◽  
...  
Keyword(s):  
Ionic Wind ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition ◽  
Transition Delay

scholarly journals Effect of aspect ratio and inlet manifold shape on the laminar-to-turbulent transition of gas flow in rectangular microchannels

2021 ◽  
Vol 62 (3) ◽  
Author(s):  
Danish Rehman ◽  
Davide Barattini ◽  
Chungpyo Hong ◽  
Gian Luca Morini
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Gas Flow ◽  
Numerical Study ◽  
Turbulent Regime ◽  
Constant Length ◽  
Rectangular Microchannels ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition ◽  
Inlet Manifold

Abstract A combined experimental and numerical study on the laminar-to-turbulent transition in microchannels using gas flow is presented. The effects of two geometric parameters, namely aspect ratio (height to width) of microchannels and inlet manifold shape, are considered on the value assumed by the critical Reynolds number linked to the laminar-to-turbulent transition. To study the effect of aspect ratio, seven rectangular microchannels having an aspect ratio between 0.25 and 1.04 are micro-milled in PMMA plastic with a constant length of 100 mm. Four rectangular microchannels with different inlet shapes, namely sudden contraction, rounded entrance, V shape and bellmouth, are fabricated to analyze the effects of inlet shape. Pressure loss analyses are then performed for all 11 microchannels by evaluating both average and semi-local friction factors. The Reynolds number in correspondence of which the transition takes place is determined by observing the trend of the friction factor. In parallel, numerical simulations using an intermittency-based transitional turbulence model are also performed and results are compared with the experiments. Experimental and numerical results have demonstrated that both of the investigated geometrical characteristics (aspect ratio and inlet manifold shape) play an important role on the range of the Reynolds number between the onset of transition and the onset of fully turbulent regime for gas microflows. Experimental critical Reynolds numbers show a good agreement with the predictions of the conventional theory and are in the range of 1863–3470 for all the tested microchannels. The role of gas compressibility on the laminar-to-turbulent transition is also discussed. Graphic abstract

scholarly journals Experimental Investigation of Transition to Turbulence as Affected by Passing Wakes

2001 ◽  
Author(s):  
Richard W. Kaszeta ◽  
Terrence W. Simon ◽  
David E. Ashpis
Keyword(s):  
Reynolds Number ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Turbine Engines ◽  
Bypass Transition ◽  
Pressure Gradients ◽  
Suction Surface ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition ◽  
Near Wall

This paper presents experimental results from a study of the effects of periodically passing wakes upon laminar-to-turbulent transition and separation in a low-pressure turbine passage. The test section geometry is designed to simulate unsteady wakes in turbine engines for studying their effects on boundary layers and separated flow regions over the suction surface by using a single suction surface and a single pressure surface to simulate a single turbine blade passage. Single-wire, thermal anemometry techniques are used to measure time-resolved and phase-averaged, wall-normal profiles of velocity, turbulence intensity and intermittency at multiple streamwise locations over the turbine airfoil suction surface. These data are compared to steady-state wake-free data collected in the same geometry to identify the effects of wakes upon laminar-to-turbulent transition. Results are presented for flows with a Reynolds number based on suction surface length and stage exit velocity of 50,000 and an approach flow turbulence intensity of 2.5%. While both existing design and experimental data are primarily concerned with higher Reynolds number flows (Re > 100,000), recent advances in gas turbine engines, and the accompanying increase in laminar and transitional flow effects, have made low-Re research increasingly important. From the presented data, the effects of passing wakes on transition and separation in the boundary layer, due to both increased turbulence levels and varying streamwise pressure gradients are presented. The results show how the wakes affect transition. The wakes affect the flow by virtue of their difference in turbulence levels and scales from those of the free-stream and by virtue of their ensemble-averaged velocity deficits, relative to the free-stream velocity, and the concomitant changes in angle of attack and temporal pressure gradients. The relationships between the velocity oscillations in the freestream and the unsteady velocity profile shapes in the near-wall flow are described. In this discussion is support for the theory that bypass transition is a response of the near-wall viscous layer to pressure fluctuations imposed upon it from the free-stream flow. Recent transition models are based on that premise. The data also show a significant lag between when the wake is present over the surface and when transition begins.

scholarly journals On the role of adaptivity for robust laminar flow control

2015 ◽  
Vol 767 ◽  
Author(s):  
Nicolò Fabbiane ◽  
Bernhard Simon ◽  
Felix Fischer ◽  
Sven Grundmann ◽  
Shervin Bagheri ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Numerical Simulations ◽  
Boundary Layer Flows ◽  
Linear Quadratic ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition ◽  
Optimal Linear ◽  
Order Of Magnitude ◽  
Tollmien Schlichting ◽  
Laminar Flow Control

AbstractIn boundary-layer flows, one may reduce skin-friction drag by delaying the onset of laminar-to-turbulent transition via the attenuation of small-amplitude Tollmien–Schlichting (TS) waves. In this work, we use numerical simulations and experiments to compare the robustness of adaptive and model-based techniques for reducing the growth of two-dimensional TS disturbances. In numerical simulations, the optimal linear quadratic Gaussian (LQG) regulator shows the best performance under the conditions it was designed for. However, it is found that the performance deteriorates linearly with the drift of the Reynolds number from its nominal value. As a result, an order-of-magnitude loss of performance is observed when applying the computation-based LQG controller in wind-tunnel experiments. In contrast, it is shown that the adaptive filtered-X least-mean-squares (FXLMS) algorithm is able to maintain an essentially constant performance for significant deviations of the nominal values of the disturbance amplitude and Reynolds number.

scholarly journals Numerical Prediction of the Tonal Airborne Noise for a NACA 0012 Aerofoil at Moderate Reynolds Number Using a Transitional URANS Approach

2017 ◽  
Vol 42 (4) ◽  
pp. 653-675 ◽  
Author(s):  
Michele De Gennaro ◽  
Helmut Kühnelt ◽  
Alessandro Zanon
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Acoustic Analogy ◽  
Tonal Structure ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition ◽  
Moderate Reynolds Number ◽  
Airborne Noise ◽  
Naca 0012

Abstract Tonal airborne noise of aerofoils appears in a limited range of moderate Reynolds numbers and angles of attack. In these specific conditions, the aerofoil is characterised by a large region of laminar flow over the aerodynamic surface, typically resulting in two-dimensional laminar instabilities in the boundary layer, generating one or more acoustic tones. The numerical simulation of such phenomenon requires, beside an accurate prediction of the unsteady flow field, a proper modelling of the laminar to turbulent transition of the boundary layer, which generally imposes the use of highly CPU demanding approaches such as large eddy simulation (LES) or direct numerical simulation (DNS). This paper aims at presenting the results of numerical experiments for evaluating the capability of capturing the tonal airborne noise by using an advanced, yet low computationally demanding, unsteady Reynolds-averaged Navier-Stokes (URANS) turbulence model augmented with a transitional model to account for the laminar to turbulent transition. This approach, coupled with the Ffowcs Williams and Hawkings (FW-H) acoustic analogy, is adopted for predicting the far-field acoustic sound pressure of a NACA 0012 aerofoil with Reynolds number ranging from 0.39 · 106 to 1.09 · 106. The results show a main tone located approximately at 1.6-1.8 kHz for a Reynolds number equal to 0.62 · 106, increasing to 2.4 kHz at Reynolds number equal to 0.85 · 106 and 3.4 kHz at 1.09 · 106, while no main tones are observed at 0.39 · 106. The computed spectra confirm that the acoustic emission of the aerofoil is dominated by tonal structures and that the frequency of the main tone depends on the Reynolds number consistently with the ladder-like tonal structure suggested by Paterson et al. Moreover, in specific conditions, the acoustic spectra exhibit a multi-tonal structure visible in narrowband spectra, in line with the findings of Arbey and Bataille. The presented results demonstrate the capability of the numerical model of predicting the physics of the tonal airborne noise generation.

Experimental Determination of Transition to Turbulence in a Rectangular Channel With Eddy Promoters

1994 ◽  
Vol 116 (3) ◽  
pp. 484-487 ◽  
Author(s):  
J. S. Kapat ◽  
J. Ratnathicam ◽  
B. B. Mikic´
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Rectangular Channel ◽  
Transition To Turbulence ◽  
Channel Height ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition ◽  
Power Spectral ◽  
Unstable Configuration

We report on laminar-to-turbulent transition in a rectangular channel in the presence of periodically placed cylindrical eddy promoters. Transition is identified through the analysis of power spectral density (PSD) of velocity fluctuations. Placement of the eddy promoters in the channel, depending on the geometric configuration, can significantly reduce the value of Reynolds number at transition. The critical Reynolds number (based on the average velocity and the channel height) ranges from 1500 (for an unobstructed channel) to about 400 (for the most unstable configuration we have deployed). For all the configurations tested, demarcation of transition can be correlated with the expression: Reτ≡τ¯w,αv/ρH/2/ν=44˜51, where τw,αv is the spatially averaged value of mean wall shear stress and H is the channel height.

scholarly journals Design and Validation of a Recirculating, High-Reynolds Number Water Tunnel

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Brian R. Elbing ◽  
Libin Daniel ◽  
Yasaman Farsiani ◽  
Christopher E. Petrin
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Test Section ◽  
High Reynolds Number ◽  
Water Tunnel ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition ◽  
Profile Matching ◽  
Final Design ◽  
High Reynolds

Commercial water tunnels typically generate a momentum thickness based Reynolds number (Reθ) ∼1000, which is slightly above the laminar to turbulent transition. The current work compiles the literature on the design of high-Reynolds number facilities and uses it to design a high-Reynolds number recirculating water tunnel that spans the range between commercial water tunnels and the largest in the world. The final design has a 1.1 m long test-section with a 152 mm square cross section that can reach speed of 10 m/s, which corresponds to Reθ=15,000. Flow conditioning via a tandem configuration of honeycombs and settling-chambers combined with an 8.5:1 area contraction resulted in an average test-section inlet turbulence level <0.3% and negligible mean shear in the test-section core. The developing boundary layer on the test-section walls conform to a canonical zero-pressure-gradient (ZPG) flat-plate turbulent boundary layer (TBL) with the outer variable scaled profile matching a 1/7th power-law fit, inner variable scaled velocity profiles matching the log-law and a shape factor of 1.3.

Visualization of Flow Field and Wake over Clean and Under-Loaded Wings

2014 ◽  
Vol 629 ◽  
pp. 24-29
Author(s):  
Hussain H. Al-Kayiem
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Flow Field ◽  
Visualization Technique ◽  
High Lift ◽  
Laminar To Turbulent Transition ◽  
Turbulent Transition ◽  
Wake Interaction ◽  
Airfoil Flow ◽  
External Body

Experimental details of the flow field and wake over airfoils and 2-D wings are time and cost consumption. In this study, the flow visualization technique was adopted to investigate the flow field surrounding NACA4412 airfoil. The investigations were carried out in smoke tunnel, operating at low Reynolds number in a range of 105. The airfoil was tested in two operational cases: first as clean wing and the second as under-loaded wing by attached missile model. The experiments were conducted at various angles of attack as 00, 50,100, 150and 200. It was found that the under-load of external body under the wing is influencing the flow structure over the wing. Also, the wake after the external body is swirling, leading to very complicated wake interaction. The results from the work can support the numerical simulation and the prediction of the laminar to turbulent transition and the separation and wake interaction of high lift airfoil flow fields.

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