Experimental study of laminar separation phenomenon combining with numerical calculations

Abstract

The separation is much more sensitive for laminar flow than for turbulent flow. These remarks have been attested for both subsonic and supersonic flows. However, they are not applicable to transonic flows when there are interactions between boundary layer and shock wave. Along with the Reynolds number, the Mach number is a necessary dimensionless parameter for the condition and the mechanism of separations. The report presents one part of studies on laminar separation with Mach number of incompressible flow. The laminar regimes correspond to flows through wind turbine blades. Our experimental work for laminar separation phenomenon was carried out in a subsonic open circuit wind tunnel by taking photographs. The accuracy of experimental results basically depends on the accuracy of wind tunnel and the quality of smoke on density and constitutive materials. Experimental results permit to determine the position of separation and the form of turbulent region followed from the separation point. Numerical studies were simultaneously realized. Based on obtained experimental and numerical results, the report presents also the comparison between the laminar separation and the turbulent separation.

Identification of wind turbine testing practices and investigation of the performance benefits of closely-spaced lateral wind farm configurations

“…The observed reduction in all of the small-scale th ru s t coefficients is consistent w ith the reduced lift coefficients, reduced stall angles, and predom inance of purely lam inar separation associated w ith the NACA 0012 airfoil a t Reynolds num bers in the range of 12.800-31,400 [148,166], Geometric scaling and m atching A will result in a significantly lower…”

“…The lift, drag, and separation properties of th e NACA 0012 airfoil are significantly different at Reynolds num bers on the order of 104 th a n at Reynolds num bers on the order of 105. Experim ents conducted on a NACA 0012 airfoil a t a Reynolds num ber of 13.000 by Hung and Ngoc m easured the lam inar separation location as th e angle of attack was increased[166]. Lam inar separation occurred over the airfoil and th ere was no evidence of lam inar-to-turbulent transition[166].…”

“…Experim ents conducted on a NACA 0012 airfoil a t a Reynolds num ber of 13.000 by Hung and Ngoc m easured the lam inar separation location as th e angle of attack was increased[166]. Lam inar separation occurred over the airfoil and th ere was no evidence of lam inar-to-turbulent transition[166]. D irect N um erical Sim ulations of a NACA 0012 airfoil at a Reynolds num ber of 50,000 perform ed by Lehm kuhl et al indicated th a t a long lam inar separation bubble was present over approxim ately 50% of th e chord of the airfoil and th a t the resulting tu rb u len t flow reattached[167], T he form ation of a small lam inar separation bubble and the associated lam inar-to-turbulent tran sitio n over the u p p er surface of an airfoil has been observed a t Reynolds num bers on the order of 1 0 5 by T anaka[168], Additionally, the experim ental work of Laitone has indicated th a t the m axim um lift coefficient (CTmttX) of a NACA 0012 airfoil a t a Reynolds num ber of 20.700 was approxim ately 0.45 and occurred a t a low angle of attack of 5.5°[148], By com parison, th e NACA 0012 airfoil has been dem onstrated to have a C i max of 0.85 at an angle of a tta c k of 9° a t Reynolds num ber of 160,000[169].…”

Experiments and numerical calculation to determine aerodynamic characteristics of flows around 3D wings

“…If taking λ > 5.2, measurement results will be wrong due to the influence of the effect of wind tunnel walls. If the experiment is done for the 2D case in this wind tunnel, the aspect ratio is then λ = 8, that is considered as infinite wingspan (as 2D problem) and we have done with them in [6,7], see also [8]. • ), and lift coefficient on wingspan (α = 2…”

Experiments and Numerical Calculation to Determine Aerodynamic Characteristics of Flows Around 3d Wings

“…If taking λ > 5.2, measurement results will be wrong due to the influence of the effect of wind tunnel walls. If the experiment is done for the 2D case in this wind tunnel, the aspect ratio is then λ = 8, that is considered as infinite wingspan (as 2D problem) and we have done with them in [6,7], see also [8]. Fig.…”