Flow analysis of airfoil having different cavities on its suction surface
07 Mar 2016-Progress in Computational Fluid Dynamics (Inderscience Publishers (IEL))-Vol. 16, Iss: 2, pp 67
TL;DR: In this paper, the fluid flow analysis of a symmetric airfoil having circular cavities on its suction surface at three different chordwise locations from leading to trailing edges is presented.
Abstract: The paper presents the fluid flow analysis of a symmetric airfoil having circular cavities on its suction surface at three different chordwise locations from leading to trailing edges. The leading edge cavity shapes were distorted using Bezier polynomial so that vortex trapping pattern in the cavities can be captured. Structured meshing scheme via a multi-block strategy was employed. Unsteady simulations were performed by a Reynolds averaged Navier-Stokes (RANS) solver. Lift, drag, pressure and skin friction coefficients were monitored at Reynolds number (Re) = 15 × 104 and 6 × 105 and different angles of attack. Cavity placed at the trailing edge produced better lift to drag ratio as compared to that of the other cavities. The distorted cavities performed badly in terms of lift and drag coefficients. The elliptical cavity shape showed better results at the angles of attack up to 10°.
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01 Oct 2019
TL;DR: In this paper, numerical investigation of the turbulent flow over a biconvex airfoil at compressible and high Mach numbers flow is done using computational fluid dynamics (CFD).
Abstract: In the present study, numerical investigation of the turbulent flow over a biconvex airfoil at compressible and high Mach numbers flow is done using computational fluid dynamics (CFD). The flow is considered as turbulent, two-dimensional, steady and compressible. For this purpose, three Reynolds number of 2.4 × 107, 2.9 × 107 and 3.3 × 107 are considered. The simulations are implemented using the commercial software Ansys Fluent 16. The results are obtained with Reynolds-averaged Navier–Stokes (RANS), and for simulating the flow turbulence, SST k–ω turbulence model is carried out. The results show that the lift coefficient (CL) and drag coefficient (CD) increase by the increment of the angle of attack (α). The lift-to-drag ratio (CL/CD) is improved by increasing the Mach number (Ma) and cause to delay the boundary layer separation. Increasing the Mach number affects the stall angle which causes to increase it from α = 22° to α = 30° from Ma = 1 to Ma = 1.4.
2 citations
TL;DR: In this paper , the effect of circular cavity on aerodynamic performance of the H-Darrieus rotor is investigated using a subsonic wind tunnel test facility to check which side cavity on the airfoil (inner or outer side) is beneficial in terms of the rotor's static and dynamic performances.
Abstract: This present investigation is carried out to improve the performance of H-Darrieus wind turbine in the built environment, where it mostly experiences low wind speed. Here the effect of circular cavity on aerodynamic performance of the rotor is investigated using a subsonic wind tunnel test facility to check which side cavity on the airfoil (inner or outer side) is beneficial in terms of the rotor’s static and dynamic performances. For this, S1046 and NACA 0021 airfoil blades are considered at various low wind speeds of 5, 6 and 7 m/s for different rotor aspect ratios. A Computational Fluid Dynamics (CFD) study is also simultaneously conducted to realize the intrinsic flow physics of the cavity airfoil blade profile. Results show that inner surface cavity on both the blades improves their self-starting ability but only at 5 m/s wind speed, which is not so when wind speed is 7 m/s at which NACA 0021 blade without cavity performs better. Again, NACA 0021 blade without cavity exhibits the highest performance of all the considered blade shapes, for which the highest power coefficient of 0.15 is achieved at a tip speed ratio of 1.25 and wind speed 6 m/s. At wind speed 7 m/s, the NACA 0021 blade rotor having outside cavity has a lower maximum power coefficient but wider operating range than that of NACA 0021 blade without cavity. CFD results show that H-Darrieus rotor having NACA 0021 blades at 30° azimuthal angle with circular cavity at 1/4th chord distance from its leading edge located at its inner surface, can generate higher lift force. However, circular cavity will be useful for starting performance of H-Darrieus rotor, which is not so for its dynamic performance, although operating range is improved.
2 citations
30 Sep 2021
TL;DR: In this paper, the authors present a numerical validation study using the experimental data collected by the National Renewable Energy Laboratory (NREL). All the simulations are performed on the sequence S of the extensive experimental sequences conducted at the NASA/Ames wind tunnel with constant RPM and variable wind speeds.
Abstract: Numerical modelling and simulation of a rotating, tapered, and twisted three-dimensional blade with turbulent inflow conditions and separating flows is a challenging case in Computational Fluid Dynamics (CFD). The numerical simulation of the fluid flow behaviour over a wind turbine blade is important for the design of efficient machines. This paper presents a numerical validation study using the experimental data collected by the National Renewable Energy Laboratory (NREL). All the simulations are performed on the sequence S of the extensive experimental sequences conducted at the NASA/Ames wind tunnel with constant RPM and variable wind speeds. The results show close agreement with the NREL UAE experimental data. The CFD model captures closely the totality of the defining quantities. The shaft torque is well-predicted pre-stall but under-predicted in the stall region. The three-dimensional flow and stall are well captured and demonstrated in this paper. Results show attached flow in the pre-stall region. The separation appears at a wind speed of 10 m/s near the blade root. For V>10m/s, the blade appears to experience a deep stall from root to tip.
2 citations
TL;DR: In this article, a highly cambered and loaded stationary fan blade cascade of an in-service centrifugal fan is analyzed at flow conditions corresponding to design point operation of subject fan, where vortex shedding from blade leading edge and its interaction with pressure side surface of adjacent blade becomes one of major source in the aeroacoustics signature of blade array.
Abstract:
A highly cambered and loaded stationary fan blade cascade of an in-service centrifugal fan is analyzed in this research work at flow conditions corresponding to design point operation of subject fan. The configuration of enclosed blade cascade includes upstream and downstream ducts. A preliminary analysis of flow variables and nearfield acoustic spectra is carried out experimentally which then provided boundary conditions and validation data for an extensive numerical analysis using embedded large eddy simulation turbulence model in ansysfluent 19.0 environment. The comprehensive analysis of flow field and nearfield aeroacoustics of blade array configuration reveals vortex shedding from blade leading edge and its interaction with pressure side surface of adjacent blade becomes one of major source in the aeroacoustics signature of blade array. The vortex shedding frequency and the frequency of upstream turbulence interaction with blade leading edge are identified. A novel method of placing rectangular cavity on pressure side of blade array to suppress the impact of impingement of leading-edge vortex via cavity acoustic wave is explored. The numerical results reveal a reduction in noise by 6 dB encouraging the efficacy of this method as a passive technique to reduce aeroacoustics signature of researched blade array configuration.
1 citations
TL;DR: In this article , the aerodynamic performance of a NACA 4412 airfoil that was modified for circulation control to determine the influence of the trailing-edge geometry, blowing coefficient, angle of attack, and height above the ground to improve the efficiency of a wing-in-ground craft and shorten its take-off distance.
Abstract: The concept of active circulation control has been proposed to improve lifting performance for various applications. It is mostly suggested as a flow control system to replace or minimize mechanical flaps or as a boundary layer control mechanism in the aerospace industry. The efficiency of these systems has always been the main concern due to increased drag and pumping requirements. These concerns are negligible for high-speed marine crafts as the hydrodynamic drag acting on the hull is dominant. This research investigates the aerodynamic performance of a NACA 4412 airfoil that was modified for circulation control to determine the influence of the trailing-edge geometry, blowing coefficient, angle of attack, and height above the ground to improve the efficiency of a wing-in-ground craft and shorten its take-off distance. The flow is subsonic and incompressible, and the chord Reynolds number is 1.7 × 106. A computational fluid dynamics investigation has determined that significant increases in lift can be attained through circulation control relative to the original NACA 4412 airfoil, and it is not significantly influenced by the airfoil height except when there is an extreme ground effect. Also, the lift augmentation increases approximately linearly with the blowing momentum coefficient and angle of attack. The study shows a significant improvement in the take-off length, which was reduced from 465 m to between 360 and 150 m according to the height above the ground plane, angle of attack, and the momentum coefficient when the Coanda surface is 30 mm. The circulation-controlled NACA 4412 could achieve 66% effectiveness compared to a currently available vehicle.