PIV Measurement of Separation Bubble on an Airfoil at Low Reynolds Numbers

Park, Donghun; Shim, Ho-Joon; Lee, Yung-Gyo

doi:10.1061/(asce)as.1943-5525.0001099

Cited by 10 publications

(6 citation statements)

References 35 publications

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“…Increasing Reynolds number from 8.4 × 10 4 to 1.7 × 10 5 slightly moved the separation point upstream on the suction side (Figure 5 and Figure 6). This pattern was also mentioned by another author [46]. The laminar separation bubble located in the adverse pressure gradient can be categories into a short and long bubbles.…”

Section: Mean Aerodynamic Characteristicssupporting

confidence: 65%

Laminar Separation Bubble and Flow Topology of NACA 0015 at Low Reynolds Number

Ibren

Andan

Asrar

et al. 2021

CFDL

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The development of sophisticated unmanned aerial vehicles and wind turbines for daily activities has triggered the interest of researchers. However, understanding the flow phenomena is a strenuous task due to the complexity of the flow field. The engaging topic calls for more research at low Reynolds numbers. The computational investigations on a two-dimensional (2D) airfoil are presented in this paper. Numerical simulation of unsteady, laminar-turbulent flow around NACA 0015 airfoil was performed by using shear-stress transport (SST) model at relatively low Reynolds number (8.4 × 104 to 1.7 × 105) and moderate angles of attack (0 ≤ α ≤ 6). In general, on the suction side, with increasing Reynolds number and angles of attack, separation, and reattachment point shifts upstream and concurrently shrinking the size of the laminar bubble. However, On the pressure side, the laminar bubble is seen to move toward the trailing edge at the relatively same size as the angle of attack increases. Moreover, the variations in the angle of attack have more influence on the laminar separation bubble characteristics as compared to the Reynolds number. The reattachment points were barely observed for the range of the angles of attack studied. At very high angles of attack, it is recommended to simulate the flow field using large eddy simulation or direct numerical simulation since the flow is considered three-dimensional and detached from the surface thus forming a complex phenomenon.

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Section: Mean Aerodynamic Characteristicssupporting

confidence: 65%

Laminar Separation Bubble and Flow Topology of NACA 0015 at Low Reynolds Number

Ibren

Andan

Asrar

et al. 2021

CFDL

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“…Thus, the size of the bubble has significant impact on the aerodynamic performance. Various experimental studies are done to understand the formation and characteristics of LSB was reviewed by Somashekar (8) and Park (9) and therefore are not repeated here. Instead, the current understanding of the characteristics of LSB and the studies validating the capability of RANS based turbulence model in predicting LSB is briefly reviewed.…”

Section: Introductionmentioning

confidence: 99%

Steady and Time Dependent Study of Laminar Separation Bubble (LSB) behavior along UAV Airfoil RG-15

2023

IJM

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The flow around the Unmanned Arial Vehicle (UAV) operating at a low Reynolds number regime of the O(10 5 ) is predominantly laminar and it leads to the formation of Laminar Separation Bubble (LSB). The pressure, shear stress, and heat flux distribution are considerably affected by LSB, which affects lift, drag, and pitching moment values. Most existing RANS (Reynolds-Averaged Navier-Stokes) turbulence models are built on the assumption of fully turbulent flow. Therefore, these models require additional transport equations or reformulations or specific transition information to predict the LSB observed in low Reynolds number transition flows. Steady and transient computational fluid dynamics simulations were done using the RANS based transition turbulence model to study the behavior of LSB on UAV airfoil RG-15. The transition turbulence model can predict the LSB with considerable accuracy. The steady state and time averaged simulation results are matching in the pre stall region but deviates after stalling. High amplitude velocity fluctuations were observed near regions of transition and separation.

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“…At the angle of attack of 7°, a short separation bubble appears with a maximum shear stress upstream of the reattachment point, while at angle of attack of 9°, the maximum shear stress is found to be far from the reattachment point. Park et al (2020) conducted measurements on DAE51 aerofoil using particle image velocimetry (PIV) at five Reynolds numbers from 3.9 3 10 4 to 1.18 3 10 5 at angles of attack ranging from 0°to 10°. It was found that the formation of the separation bubble depends mainly on the Reynolds number and angle of attack.…”

Section: Introductionmentioning

confidence: 99%

“…The laminar separation bubble (LSB) is formed in many practical flows as laminar boundary layer separation, transition to turbulence, and reattachment as shown in Figure 1(a). The length of the LSB depends on the transition process in the shear layer along with Reynolds numbers, angles of attack, and geometric shape of the aerofoil (Park et al, 2020). The appearance of the LSB can cause a significant influence on the aerodynamic characteristics of the aerofoil, such as aerodynamic noise, flow instability, decrease in lift and increase in pressure drag forces (Kojima et al, 2013; Winslow et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

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The influence of the flow separation bubble and transition location on the profile drag of three 4-digit NACA aerofoil profiles

Elgammi¹,

Sant

Ateeah

2021

Wind Engineering

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Modeling of the flow over aerofoil profiles at low Reynolds numbers is difficult due to the complex physics associated with the laminar flow separation mechanism. Two major problems arise in the estimation of profile drag: (1) the drag force at low Reynolds numbers is extremely small to be measured in a wind tunnel by force balance techniques, (2) the profile drag is usually calculated by pressure integration, hence the skin friction component of drag is excluded. In the present work, three different 4-digit NACA aerofoils are investigated. Measurements are conducted in an open-ended subsonic wind tunnel, while numerical work is performed by time Reynolds-averaged Navier Stokes (RANS) coupled with the laminar-kinetic-energy ( K-kl-w) turbulence model. The influence of the flow separation bubbles and transition locations on the profile drag is discussed and addressed. This paper gives important insights into importance of measurements at low Reynolds numbers for better aerodynamic loads predictions.

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PIV Measurement of Separation Bubble on an Airfoil at Low Reynolds Numbers

Cited by 10 publications

References 35 publications

Laminar Separation Bubble and Flow Topology of NACA 0015 at Low Reynolds Number

Laminar Separation Bubble and Flow Topology of NACA 0015 at Low Reynolds Number

Steady and Time Dependent Study of Laminar Separation Bubble (LSB) behavior along UAV Airfoil RG-15

The influence of the flow separation bubble and transition location on the profile drag of three 4-digit NACA aerofoil profiles

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