NUMERICAL STUDY OF FLOW SEPARATION CONTROL OVER A NACA 2415 AIRFOIL

This study involves numerical simulation of the flow around a NACA2415 airfoil, with a 18°angle of attack, and flow separation control using a rod, It involves putting a cylindrical rod -placing upstream of the leading edge- in vertical translator movement in order to accelerate the transition of the boundary layer by interaction between the wake behind the rod and the boundary layer. The viscous, non-stationary flow is simulated using ANSYS FLUENT 13. The rod movement is reproduced using the dynamic mesh technique and an in-house developed UDF (User Define Function).The frequency varies from 75 to 450 Hz and the considered amplitudes are 2%, and 3% of the foil chord. The frequency chosen closed to the natural frequency of separation, and the rod diameter is equal to 2% the foil cord. Our results show a substantial modification in the structure of the flow and a maximum drag reduction of 61%

NUMERICAL STUDY OF FLOW SEPARATION CONTROL OVER A NACA 2415 AIRFOIL

This study involves numerical simulation of the flow around a NACA2415 airfoil, with a 18°angle of attack, and flow separation control using a rod, It involves putting a cylindrical rod -placing upstream of the leading edge- in vertical translator movement in order to accelerate the transition of the boundary layer by interaction between the wake behind the rod and the boundary layer. The viscous, non-stationary flow is simulated using ANSYS FLUENT 13. The rod movement is reproduced using the dynamic mesh technique and an in-house developed UDF (User Define Function).The frequency varies from 75 to 450 Hz and the considered amplitudes are 2%, and 3% of the foil chord. The frequency chosen closed to the natural frequency of separation, and the rod diameter is equal to 2% the foil cord. Our results show a substantial modification in the structure of the flow and a maximum drag reduction of 61%

Effects of Non-Sinusoidal Motion and Effective Angle of Attack on Energy Extraction Performance of a Fully- Activated Flapping Foil

Flapping foil energy harvesting systems are considered as highly competitive devices for conventional turbines. Several research projects have already been carried out to improve performances of such new devices. This paper is devoted to study effects of non-sinusoidal heaving trajectory, non-sinusoidal pitching trajectory, and the effective angle of attack on the energy extraction performances of a flapping foil operating at low Reynolds number (Re=1100). An elliptic function with an adjustable parameter S (flattening parameter) is used to simulate various sinusoidal and non-sinusoidal flapping trajectories. The flow around the flapping foil is simulated by solving Navier–Stokes equations using the commercial software Star CCM+ based on the finite-volume method. Overset mesh technique is used to model the flapping motion. The study is applied to the NACA0015 foil with the following kinetic parameters: a dimensionless heaving amplitude h0 = 1c, a shift angle between heaving and pitching motions f = 90 , a reduced frequency f = 0:14, and an effective angle of attack amax varying between 15 and 50 , corresponding to a pitching amplitude in the range q0 = 55:51 to 90:51 . The results show that, the non-sinusoidal trajectory affects considerably the energy extraction performances. For the reference case (sinusoidal heaving and pitching motions, Sh = Sq = 1), best performances are obtained for the effective angle of attack, amax = 40 . At small effective angle of attack amax 40 ), non-sinusoidal pitching motion has a negative effect. Performance improvement is quite limited with the combined motions non-sinusoidal heaving/sinusoidal pitching

Energy extraction performance improvement of a flapping foil by the use of combined foil

In this study, numerical investigations on the energy extraction performance of a flapping foil device are carried out by using a modified foil shape. The new foil shape is designed by combining the thick leading edge of NACA0012 foil and the thin trailing edge of NACA0006 foil. The numerical simulations are based on the solution of the unsteady and incompressible Navier-Stokes equations that govern the fluid flow around the flapping foil. These equations are resolved in a two-dimensional domain with a dynamic mesh technique using the CFD software ANSYS Fluent 16. A User Define Function (UDF) controls the imposed sinusoidal heaving and pitching motions. First, for a validation study, numerical simulations are performed for a NACA0012 foil undergoing imposed heaving and pitching motions at a low Reynolds number. The obtained results are in good agreement with numerical and experimental data available in the literature. Thereafter, the computations are applied for the new foil shape. The influences of the connecting area location between the leading and trailing segments, the Strouhal number and the effective angle of attack on the energy extraction performance are investigated at low Reynolds number (Re = 10 000). Then, the new foil shape performance was compared to those of both NACA0006 and NACA0012 baseline foils. The results have shown that the proposed foil shape achieves higher performance compared to the baseline NACA foils. Moreover, the energy extraction efficiency was improved by 30.60% compared to NACA0006 and by 17.32% compared to NACA0012. The analysis of the flow field around the flapping foils indicates a change of the vortex structure and the pressure distribution near the trailing edge of the combined foil compared to the baseline foils

Numerical Investigation of the Effects of Nonsinusoidal Motion Trajectory on the Propulsion Mechanisms of a Flapping Airfoil

The effect of nonsinusoidal trajectory on the propulsive performances and the vortex shedding process behind a flapping airfoil is investigated in this study. A movement of a rigid NACA0012 airfoil undergoing a combined heaving and pitching motions at low Reynolds number (Re¼11,000) is considered. An elliptic function with an adjustable parameter S (flattening parameter) is used to realize various nonsinusoidal trajectories of both motions. The two-dimensional (2D) unsteady and incompressible Navier–Stokes equation governing the flow over the flapping airfoil are resolved using the commercial software STAR CCMþ. It is shown that the nonsinusoidal flapping motion has a major effect on the propulsive performances of the flapping airfoil. Although the maximum propulsive efficiency is always achievable with sinusoidal trajectories, nonsinusoidal trajectories are found to considerably improve performance: a 110% increase of the thrust force was obtained in the best studied case. This improvement is mainly related to the modification of the heaving motion, more specifically the increase of the heaving speed at maximum pitching angle of the foil. The analysis of the flow vorticity and wake structure also enables to explain the drop of the propulsive efficiency for nonsinusoidal trajectories

Large eddy simulation of flow Separation Control over a NACA 2415 airfoil

This study involves numerical simulation of the flow around a NACA2415 airfoil, with a 15°angle of attack, and flow separation control using a rod, It involves putting a cylindrical rod in the upstream of the leading edge in order to accelerate the transition of the boundary layer by interaction between the wake behind the rod and the boundary layer. The viscous, non-stationary flow is simulated using ANSYS FLUENT 13. Our results show a substantial modification in the flow structure and a maximum drag reduction of 51%

NUMERICAL STUDY OF FLOW SEPARATION CONTROL OVER A NACA 2415 AIRFOIL

This study involves numerical simulation of the flow around a NACA2415 airfoil, with a 18°angle of attack, and flow separation control using a rod, It involves putting a cylindrical rod -placing upstream of the leading edge- in vertical translator movement in order to accelerate the transition of the boundary layer by interaction between the wake behind the rod and the boundary layer. The viscous, non-stationary flow is simulated using ANSYS FLUENT 13. The rod movement is reproduced using the dynamic mesh technique and an in-house developed UDF (User Define Function).The frequency varies from 75 to 450 Hz and the considered amplitudes are 2%, and 3% of the foil chord. The frequency chosen closed to the natural frequency of separation, and the rod diameter is equal to 2% the foil cord. Our results show a substantial modification in the structure of the flow and a maximum drag reduction of 61%

Large eddy simulation of flow Separation Control over a NACA 2415 airfoil

This study involves numerical simulation of the flow around a NACA2415 airfoil, with a 15°angle of attack, and flow separation control using a rod, It involves putting a cylindrical rod in the upstream of the leading edge in order to accelerate the transition of the boundary layer by interaction between the wake behind the rod and the boundary layer. The viscous, non-stationary flow is simulated using ANSYS FLUENT 13. Our results show a substantial modification in the flow structure and a maximum drag reduction of 51%

Experimental and Numerical study on Aerodynamics of Aerofoils at Low Reynolds Number Controlled by Off-Surface Micro-Vortex Generators

International audienceA passive flow control strategy for four different aerofoils (NACA0012, NACA6415, S809 and S8036) operating at low Reynolds number applications, was investigated in the current work. The effect of installing micro off-surface rod device with various cross-section shapes (circular, triangular, square, pentagonal and hexagonal) in the vicinity of aerofoils leading edge at flow condition Re c = 2.5 × 10 5 was experimentally and numerically investigated. A common diameter for each given rod was set to be d/c = 1.34%, where c is the aerofoil chord length. The streamwise in-line and the top cross-stream offset dimensionless spacings were the two parameters that have been considered. Their scaling influence on the flow control effectiveness through aerodynamic loads analysis was examined by mean of wind tunnel measurements. Steady RANS calculations with transition sensitive closure turbulence model (γ − Re θ,t) were further supplemented to provide more insights about this flow control method. The main results revealed that these off-surface micro-vortex generators are very effective in controlling the flow at post stall regime for all aerofoils. First, the parasite drag for rod-aerofoil system is small at low incidence angles for both NACA6415 and S809 wings compared to S8036. In the other hand, significant enhancement in lift coefficient can be achieved at post stall, accompanying by pronounced decrease in drag coefficient for all configurations. In addition, results indicate that the heavy stall can be effectively delayed for higher angles