Measurements of water film characteristics on airfol surfaces from wind-tunnel tests with simulated heavy rain

Hastings, E. C.; Manuel, Gregory S.

doi:10.2514/6.1985-259

Cited by 5 publications

(5 citation statements)

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“…For this initial condition* -= 0.15 and o 50. These values were chosen to be representative of conditions discussed by Hastings and Manuel (1985), in which they describe the results of their wind tunnel measurements of a wing in simulated rain. In the above profile, for 0 < T) < i*, f' is parabolic with f".…”

Section: Evolution Of a Profile Which Is Initially Parabolic In Segmementioning

confidence: 99%

Boundary layer flow of air over water on a flat plate

1995

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A non-similar boundary layer theory for air blowing over a water layer on a flat plate is formulated and studied as a two-fluid problem in which the position of the interface is unknown. The problem is considered at large Reynolds number (based on x), away from the leading edge. We derive a simple non-similar analytic solution of the problem for which the interface height is proportional to x1/4 and the water and air flow satisfy the Blasius boundary layer equations, with a linear profile in the water and a Blasius profile in the air. Numerical studies of the initial value problem suggest that this asymptotic non-similar air–water boundary layer solution is a global attractor for all initial conditions.

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Section: Evolution Of a Profile Which Is Initially Parabolic In Segmementioning

confidence: 99%

Boundary layer flow of air over water on a flat plate

1995

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“…Indeed this has been observed by various researchers who conducted experiments with test wing sections in wind tunnels under conditions that simulate rainfall. As was mentioned in the introduction, Feo & Gonzalez (1988) and Hastings & Manuel (1985), among others, measured film thickness characteristics in the wind tunnel facility at NASA-Langley, and they captured the increase in film thickness with increasing rainfall rate, or equivalently with increasing liquid water content in the air stream, and decreasing free-stream velocity, or with decreasing Reynolds number in the gas stream. In addition, they observed the formation of longitudinal waves in the region 0.1 6 x /c 6 0.5 of a NACA 64-210 airfoil followed by three-dimensional rivulets.…”

Section: Solution Valid When X ∼mentioning

confidence: 99%

“…In fact, intense rainfall and high wind shear are believed to have caused a number of aircraft accidents that occurred under adverse weather conditions. Experimental investigations conducted at the NASA-Langley Low-Speed Wind-Tunnel facility (Hastings & Manuel 1985;Feo & Gonzalez 1988) captured the evolution of a continuous film as well as the formation of longitudinal waves on its interface, on either side of a NACA 64-210 airfoil under varying simulated rainfall conditions. Measurements on the upper airfoil surface for small angles of attack revealed a trend towards larger film thickness with increasing rainfall rate,ṙ, and decreasing Reynolds number, Re.…”

Section: Introductionmentioning

confidence: 99%

Boundary layer flow of air past solid surfaces in the presence of rainfall

2000

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The steady two-dimensional laminar flow of an air stream, flowing past a solid surface at high Reynolds number, is examined in the presence of rainfall. As raindrops sediment on the surface they coalesce and form a continuous water film that flows due to shear, pressure drop and gravity, in general. In the limit as the boundary layer and film thickness remain smaller than the radius of curvature of the surface a simplified lubrication-type formulation describes the flow field in the film, whereas the usual boundary layer formulation is applied in the gas phase. In the case of a flat plate and close to the leading edge, x → 0, a piecewise-self-similar solution is obtained, according to which creeping flow conditions prevail in the film and its thickness grows like x3/4, whereas the Blasius solution is recovered in the air stream. Numerical solution of the governing equations in the two phases and for the entire range of distances from the leading edge, x = O(1), shows that the film thickness increases as the rainfall rate, r˙, increases or as the free-stream velocity, U∞, decreases and that the region of validity of the asymptotic result covers a wide range of the relevant problem parameters. In the case of flow past a NACA-0008 airfoil at zero angle of attack a Goldstein singularity may appear far downstream on the airfoil surface due to adverse pressure gradients, indicating flow reversal and eddy formation inside the liquid film, and, possibly, flow separation. However, when the effect of gravity becomes evident in the film flow, as the Froude number decreases, and provided gravity acts in such a way as to negate the effect of the adverse pressure gradient, the location of the singularity is displaced towards the trailing edge of the airfoil and the flow pattern resembles that for flow past a flat plate. The opposite happens when gravity is aligned with the adverse pressure gradient. In addition it was found that there exists a critical water film thickness beyond which the film has a lubricating effect delaying the appearance of the singularity. Below this threshold the presence of the liquid film actually enhances the formation of the singularity.

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“…Until aircraft accidents due to rainfall occurred, 4,5 studies on aerodynamic performance degradation in the rain condition were conducted by using the experimental and theoretical methods [6][7][8] in order to explore the potential causes of flight accidents. Studies on water film flow on airfoil surfaces [9][10][11] and rain erosion 12,13 were also conducted. Since then, rainfall studies have become a hot subject in the aviation world.…”

Section: Introductionmentioning

confidence: 99%

Helicopter flight dynamics with simulated rainfall

Cao

2022

Proceedings of the Institution of Mechanical Engineers, Part G:

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Sustaining flight operation that encounters with rainfall might be a challenge to a pilot due to lacking of understanding flight dynamics in the rain conditions. This paper, combined with a computational fluid dynamics (CFD) technique, develops a nonlinear flight dynamics model in the rain conditions that can be capable of exploring UH-60A single-rotor helicopter flight dynamics in the rain conditions, including trim, stability, and controllability. Firstly, in order to obtain a data-driven basis relating to multiple working conditions of the blades, a CFD-based method of simulation of the blade airfoil in the conditions of the angles of attack ranging from −26° to 26° and under a thunderstorm heavy rain scenario when the rate of rainfall is 1500 mm/h is developed. Then, these data are incorporated into a nonlinear flight dynamics model in the form of coefficient increments. Numerical simulations are conducted in the range of the flight velocities from 0 knots to 160 knots. The quantitative results indicate that rainfall degrades the blade airfoil aerodynamic performance and increases the rotor torque and required power, affecting the helicopter trim, stability, and controllability. More importantly, helicopter that flies in a small or moderate flight velocity and that encounters rainfall might be a relative serious case, which should be paid attention to.

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Measurements of water film characteristics on airfol surfaces from wind-tunnel tests with simulated heavy rain

Cited by 5 publications

References 1 publication

Boundary layer flow of air over water on a flat plate

Boundary layer flow of air over water on a flat plate

Boundary layer flow of air past solid surfaces in the presence of rainfall

Helicopter flight dynamics with simulated rainfall

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