Numerical Investigation of Turbulent Flow Around a Stepped Airfoil at High Reynolds Number

2009 ◽  
Author(s):  
Masoud Boroomand ◽  
Shirzad Hosseinverdi
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Vortex Formation ◽  
Stream Velocity ◽  
Pressure Side ◽  
Backward Facing Step ◽  
Suction Surface ◽  
Drag Ratio ◽  
Lift To Drag Ratio ◽  
Trapped Vortex

This study presents the numerical simulation of flow development around NACA-2412 airfoil which utilized the backward facing step to explore the possibility of enhancing airfoil aerodynamic performance by trapped vortex lift augmentation. This article concentrate on the effect of separated flow and following vortex formation which is created by backward facing step on pressure distribution and subsequently on lift and drag coefficient. Reynolds number that based on the free stream velocity and airfoil chord is 5.7×106. The two-equation shear stress transport (SST) k-ω turbulence model of Menter is employed to determine accurately turbulent flow, as well as the recirculation pattern along the airfoil. The Reynolds-averaged Navier Stokes (RANS) equations are solved numerically using finite volume based solution with second-order upwind Roe’s scheme. Steps are located on both suction side and pressure side of the airfoil, at different locations, different lengths and various depths in order to determine their effects on lift, lift to drag ratio and near stall behavior. The modeling results showed that all stepped airfoil cases studied experienced higher drag compared to the base airfoil. Considerable lift enhancement was found for airfoil with backward facing step on pressure side at all values of angle of attack because of trapped vortex. The results suggest that the steps on the lower surface that extended back to trailing edge can lead to more enhancement of lift to drag ratio for some angles of attack; while the rear locations for the step on upper surface was found to have negative effect on lift to drag ratio. Based on this study, the backward facing step on suction surface offers no discernable advantages over the conventional airfoil but showed some positive effect on delaying stall.

RANS Investigation of the Transitional Flow Over Stepped NLF(1)-0416

2012 ◽  
Author(s):  
Shervin Sammak ◽  
Rambod Mojgani ◽  
Masoud Boroomand
Keyword(s):  
Skin Friction ◽  
Fluid Dynamic ◽  
Leading Edge ◽  
Transitional Flow ◽  
Stream Velocity ◽  
Backward Facing Step ◽  
Suction Surface ◽  
Rans Equations ◽  
Drag Ratio ◽  
Lift To Drag Ratio

The Computational Fluid Dynamic simulation of RANS equations over NLF(1)-0416, utilized by backward facing step, is investigated for enhancement of aerodynamic characteristics. This article concentrates on the effects of step location transition point and reattachment of separated flow by backward facing step on pressure distribution and skin friction coefficient and subsequently on lift and drag. Reynolds number (based on the free stream velocity and airfoil chord) is 2.0 million. The finite volume method has been employed to numerically solve the steady state compressible Reynolds Averaged Navier-Stokes (RANS) equations with second order Roe’s scheme. Steps at different chordwise locations are chosen on both suction and pressure sides of the airfoil in order to determine their effects on skin friction, lift, lift to drag ratio and near stall behavior. In specific cases decreasing in drag is achieved due to step point on the chord followed by transition inception. The results show that all stepped studied airfoil cases experienced higher drag in comparison with base airfoil. Lift to drag ratio enhancement is seen in step on pressure side while the step extended to leading edge, this effect increases. Based on the results, delaying stall in some cases with step on suction surface is concluded.

Large-Eddy Simulations of Owl-Like Wing Under Low Reynolds Number Conditions

2013 ◽  
Author(s):  
Katsutoshi Kondo ◽  
Hikaru Aono ◽  
Taku Nonomura ◽  
Akira Oyama ◽  
Kozo Fujii ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Separation Bubble ◽  
Suction Side ◽  
Flow Fields ◽  
Pressure Side ◽  
Laminar Separation Bubble ◽  
Laminar Separation ◽  
Large Eddy ◽  
Drag Ratio ◽  
Lift To Drag Ratio

Flow fields around an owl-like wing and aerodynamic characteristics at a chord Reynolds number of 23,000 are investigated using three-dimensional implicit large-eddy simulation. The cross sectional profile of the owl wing model named “owl-like wing” is constructed based on the owl wing at 40% of the span length from the root. It consists of flat upper surface, large camber, and thin geometry. Results show that at low angles of attack (α), separation, transition, and reattachment are observed in the instantaneous flow fields on the pressure side. The laminar separation bubbles can be seen in time- and span-averaged flow fields. It is likely that lift and drag generation is correlated with the location of separation points on the suction side. However, it has little influence on behavior of CL-α curve. On the other hand, at high angles of attack, the flow on the pressure side is fully attached. The flow on the suction side is similar to that of the pressure side at low angles of attack. It is found that unlike the case of the flow at the low angles of attack, the laminar separation bubble on the suction side affects the response of CL to variation of α. Furthermore, it is possible to decrease the drag and to increase the lift when the location of the laminar separation bubble is well organized by an appropriate airfoil surface geometry. Also, the deeply concaved lower surface contributes to lift enhancement. From those factors mentioned above, the owl-like wing gains higher lift-to-drag ratio comparing with conventional thin and thick symmetrical airfoils such as NACA0002 and NACA0012. Indeed, maximum lift-to-drag ratio of the owl-like wing is approximately 23 at the angle of attack of 6.0 degrees at Reynolds number of 23,000.

scholarly journals Aerodynamic and Vibration Characteristics of the Micro-Octocopter at Low Reynolds Number

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Xiaohua Zou ◽  
Mingsheng Ling ◽  
Wenzheng Zhai
Keyword(s):  
Reynolds Number ◽  
Load Capacity ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Aerodynamic Characteristics ◽  
Vibration Characteristics ◽  
Low Reynolds ◽  
Vibration Performance ◽  
Drag Ratio ◽  
Lift To Drag Ratio

With the development of flight technology, the need for stable aerodynamic and vibration performance of the aircraft in the civil and military fields has gradually increased. In this case, the requirements for aerodynamic and vibration characteristics of the aircraft have also been strengthened. The existing four-rotor aircraft carries limited airborne equipment and payload, while the current eight-rotor aircraft adopts a plane layout. The size of the propeller is generally fixed, including the load capacity. The upper and lower tower layout analyzed in this paper can effectively solve the problems of insufficient four-axis load and unstable aerodynamic and vibration performance of the existing eight-axis aircraft. This paper takes the miniature octorotor as the research object and studies the aerodynamic characteristics of the miniature octorotor at different low Reynolds numbers, different air pressures and thicknesses, and the lift coefficient and lift-to-drag ratio, as well as the vibration under different elastic moduli and air pressure characteristics. The research algorithm adopted in this paper is the numerical method of fluid-solid cohesion and the control equation of flow field analysis. The research results show that, with the increase in the Reynolds number within a certain range, the aerodynamic characteristics of the miniature octorotor gradually become better. When the elastic modulus is 2.5 E, the aircraft’s specific performance is that the lift increases, the critical angle of attack increases, the drag decreases, the lift-to-drag ratio increases significantly, and the angle of attack decreases. However, the transition position of the flow around the airfoil surface is getting closer to the leading edge, and its state is more likely to transition from laminar flow to turbulent flow. When the unidirectional carbon fiber-reinforced thickness is 0.2 mm and the thin arc-shaped airfoil with the convex structure has a uniform thickness of 2.5% and a uniform curvature of 4.5%, the aerodynamic and vibration characteristics of the octorotor aircraft are most beneficial to flight.

Wake Interaction of a Square Cylinder With a Splitter Plate Boundary Layer at a Low Reynolds Number

2015 ◽  
Author(s):  
Smriti Srivastava ◽  
Sudipto Sarkar
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Bluff Body ◽  
Acoustic Noise ◽  
Vortex Formation ◽  
Plate Boundary ◽  
Wake Flow ◽  
Stream Velocity ◽  
Square Cylinder ◽  
Plate Length

One of the most important researches in bluff body aerodynamics is to control the shear layer evolution leading to vortex formation. This kind of research is closely associated with reduction of aerodynamics forces and acoustic noise. Passive and active control of wake-flow from bluff bodies have received a great deal of attention in the last few decades [1–4]. Keeping this in mind, authors investigate the interaction of a square cylinder (side of the square = a) wake with a flat plate (length L = a, width w = 0.1a) boundary layer positioned at various downstream locations close to the cylinder. The gap-to-side ratios are maintained at G/a = 0, 0.5, 1 and 2 (where G is the gap between square cylinder and plate), and the simulation is performed at a Reynolds number, Re = 100 (Re = U∞a/v, where U∞ is free stream velocity and v is kinematic viscosity). Instantaneous flow visualization, aerodynamic forces and vortex shedding frequencies for all cases are described to gain insight about the changes associated with wake of the cylinder when a short plate is kept in its downstream.

Experiments on Backward-Facing Step Flows Preceding a Filter

2007 ◽  
Author(s):  
S. Yao ◽  
C. Krishnamoorthy ◽  
F. W. Chambers
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Separated Flow ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Step Height ◽  
Reattachment Point ◽  
Backward Facing Step ◽  
Air Filters ◽  
Air Filter

The resistance of automotive air filters alters upstream pressure gradients and thereby affects flow separation, the velocity distributions over the filter, and the performance of the filter. Air filters provide a resistance sufficient to alter flows, but not enough to make face velocities uniform. The backward-facing step flow is an archetype with a separation that resembles those found in automotive air filter housings. To gain insight to the problem of separation and filters, experiments were conducted measuring velocity fields for air flows in a 10:1 aspect ratio rectangular duct with a backward-facing step with and without the resistance of an air filter mounted downstream. The expansion ratio for the step was 1:2. The filter was mounted 4.25 and 6.75 step heights downstream of the step; locations both upstream and downstream of the nominal 6 step-height no-filter reattachment point. Experiments were performed at four Reynolds numbers between 2000 and 10,000. The Reynolds numbers were based on step height and inlet maximum velocity. The inlet velocity profiles at the step were developed. A Laser Doppler Anemometer (LDA) was used to measure velocity profiles and map separated regions between the step and the filter. The results indicate that the filter tends to decrease the streamwise velocity on the non-separated side of the channel and increase it on the separated, step, side compared to the no-filter flow. Non-separated flow tends to separate due to the deceleration and separated flow reattaches before the filter, whether the filter is placed at 4.25 or 6.75 step heights. The literature shows that without a filter the reattachment location depends on the Reynolds number in the laminar and transitional regimes, but is constant for turbulent flow. However, the area of the reversed flow may vary with Reynolds number for turbulent flow. With the filter at 4.25 step heights, the area of reversing flow is reduced significantly, and the Reynolds number has little effect on the main properties of the flow. With the filter at 6.75 step heights, the reversing flow area decreases as the Reynolds number increases though the reattachment point is fixed just upstream of the filter.

420 Aerodynamic Characteristics and Flow Field of High Lift-to-drag Ratio Airfoils in Low Reynolds Number

2015 ◽  
Vol 2015.68 (0) ◽  
pp. 167-168 ◽  
Author(s):  
Takahiro MAKIZONO ◽  
Gaku SASAKI ◽  
Hiroshi OCHI ◽  
Takaaki MATSUMOTO ◽  
Koichi YONEMOTO
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Low Reynolds Number ◽  
Aerodynamic Characteristics ◽  
High Lift ◽  
Low Reynolds ◽  
Drag Ratio ◽  
Lift To Drag Ratio

Lift Augmentation between Passive and Active Vortex Generator

2016 ◽  
Vol 851 ◽  
pp. 532-537
Author(s):  
Nur Faraihan Zulkefli ◽  
Zulhilmy Sahwee ◽  
Nurhayati Mohd Nur ◽  
Muhamad Nor Ashraf Mohd Fazil ◽  
Muaz Mohd Shukri
Keyword(s):  
Reynolds Number ◽  
Lift Coefficient ◽  
Vortex Generator ◽  
Leading Edge ◽  
Plasma Actuator ◽  
Triangular Shape ◽  
Subsonic Wind Tunnel ◽  
Different Types ◽  
Drag Ratio ◽  
Lift To Drag Ratio

This study was conducted to investigate the performance of passive and active vortex generator on the wing’s flap. The triangular shape of passive vortex generator (VG) was developed and attached on the wing’s flap leading edge while the plasma actuator performed as active vortex generator. The test was carried out experimentally using subsonic wind tunnel with 300 angles extended flap. Three different types of turbulent flow; with Reynolds number 1.5 x105, 2.0 x105, and 2.6x105 were used to study the aerodynamics forces of airfoil with plasma actuator OFF. All Reynolds number used were below 1x106. The result indicated that airfoil with plasma actuator produced higher lift coefficient 12% and lift-to-drag ratio 5% compared to airfoil with passive vortex generator. The overall result showed that airfoil with plasma actuator produced better lift forces compared to passive vortex generator.

Numerical Study of Winglet Cant Angle Effect on Wing Performance at Low Reynolds Number

2013 ◽  
Vol 393 ◽  
pp. 366-371
Author(s):  
C.F. Mat Taib ◽  
Abdul Aziz Jaafar ◽  
Salmiah Kasolang
Keyword(s):  
Reynolds Number ◽  
Numerical Analysis ◽  
Numerical Study ◽  
Low Reynolds Number ◽  
Lift Coefficient ◽  
Wing Model ◽  
Low Reynolds ◽  
Wing Performance ◽  
Drag Ratio ◽  
Lift To Drag Ratio

The study on the effect of winglet shape in wing design has been a focus of many researchers. Nevertheless, the effect of cant angle on the wing performances at low Reynolds number has not been fully explored. This paper describes the effect of a single semi-circular shaped winglet attached with a rectangular wing model to lower the drag without increasing the span of the wing. Aerodynamic characteristics for the rectangular wing (NACA 65-3-218) with and without semi-circular winglets have been studied using STAR CCM+ 4.0. This numerical analysis is based on Finite Volume Approach. Simulations were carried out on the rectangular wing model with and without winglet at aspect ratio of 2.73 and Reynolds number of 0.16 x 10 6 for various angles of attack. From the numerical analysis, wing performance characteristics in terms of lift coefficient CL, drag coefficient CD, and lift-to-drag ratio, CL/CD were obtained. It was found that the addition of a semi-circular winglet has resulted in a larger lift curve slope and higher Lift-to-Drag ratio in comparison with the case of a wing without winglet. Further investigation has revealed that a wing with semi-circular winglet with cant angle of 45 degree has produced the best Lift-to-Drag ratio, CL/CD.

Two-dimensional impervious sails: experimental results compared with theory

1984 ◽  
Vol 144 ◽  
pp. 445-462 ◽  
Author(s):  
B. G. Newman ◽  
H. T. Low
Keyword(s):  
Reynolds Number ◽  
Dynamic Instability ◽  
Two Dimensional ◽  
Poor Agreement ◽  
Trailing Edge ◽  
Small Incidence ◽  
Visualization Experiments ◽  
Drag Ratio ◽  
Lift To Drag Ratio ◽  
Edge Flow

Experiments have been made on quasi two-dimensional sails of small camber and at small incidence. Four excess-length ratios have been tested at a Reynolds number of 1.2 x 105. The results for lift, tension, centre of lift, maximum camber and its position, and leading- and trailing-edge membrane angles have been compared with existing inviscid theories and show poor agreement in general. This is attributed to leading- and trailing-edge flow separations as indicated by supplementary flow-visualization experiments. The optimum incidences in particular are much greater than the theoretical value of 0°. Luffing occurs at slightly negative incidences and appears to be a dynamic instability. The highest lift-to-drag ratio obtained was 16.5 on a membrane with an excess-length ratio of 0.03.

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