Showing papers by "Peiqing Liu published in 2017"

Numerical Simulation of Aircraft Tire-Generated Spray and Engine Ingestion on Flooded Runways

Abstract: The aircraft water spray test on water-contaminated runways is of great significance in the civil aircraft airworthiness certification. It is a very complex strongly nonlinear multiphysics process ...

Numerical simulation of gurney flaps lift-enhancement on a low reynolds number airfoil

Abstract: Two-dimensional steady Reynolds-averaged Navier-Stokes (RANS) equations with transition shear stress transport (SST) model were solved to investigate the effects of Gurney flaps on the aerodynamic performance of a low Reynolds number airfoil. This airfoil was designed for flight vehicles operating at 20 km altitude with freestream velocity of 25 m/s. The chord length (C) of this airfoil is 5 m and the corresponding Reynolds number is 7.76×105. Gurney flaps with the heights ranging from 0.25%C to 3%C were investigated. It has been shown that Gurney flaps can enhance not only the prestall lift but also lift-to-drag ratio in a certain range of angles of attack. Specially, at cruise angle of attack (3°), Gurney flap with the height of 0.5%C can increase lift-to-drag ratio and lift coefficient by 1.6% and 12.8%, respectively. Furthermore, the mechanisms of Gurney flaps to improve the aerodynamic performance were illustrated by analyzing the surface pressure distribution, streamlines and trailing-edge flow structure for this low Reynolds number airfoil. Specially, distinguished from some other numerical researches, the flow details such as the laminar separation bubble and transition phenomena for low Reynolds number airfoil with Gurney flaps were investigated and it was found that Gurney flaps can delay the transition onset position at small angles of attack (≤2°). However, with the increase of angles of attack, Gurney flaps will promote the boundary layer transition.

Aerodynamic/mechanism optimization of a variable camber Fowler flap for general aviation aircraft

Abstract: A conventional Fowler flap is designed to improve the take-off and landing performances of an aircraft. Because the flight states of general aviation aircraft vary significantly. A Fowler flap with a double-sliding track has been designed, which is capable of changing airfoil camber while cruising and climbing as well as meeting low-speed performance requirements. The aerodynamic characteristics of the variable camber Fowler flap were studied by computational simulation, and cambering was found to be beneficial for improving the lift-to-drag ratio when the lift coefficient was larger than the critical value, below which decambering was more effective; this critical value differed somewhat under different conditions. Taking the mechanism into account, the take-off and landing configurations were optimized on the basis of the GA (W)-1 airfoil with a 30% chord Fowler flap. Compared with reference configuration, the maximum lift coefficient of optimized take-off configuration was increased by 6.6% as well as the stalling angle and the lift-to-drag ratio were increased by 1.3° and 7.58%, respectively. Moreover, the maximum lift coefficient of the optimized landing configuration was increased by 6.3%, and the stalling angle was increased by 1.1°; however, the nose-down pitching moment of both configurations increased. Similar results were attained on a general aviation aircraft wing/body combination. A 3D model of the variable-camber Fowler flap driving mechanism was established in a computer-aided design system, and the results showed that all design configurations could be achieved by the double-sliding track.

Detecting the chaotic nature in a transitional boundary layer using symbolic information-theory quantifiers.

Abstract: The permutation entropy and the statistical complexity are employed to study the boundary-layer transition induced by the surface roughness. The velocity signals measured in the transition process are analyzed with these symbolic quantifiers, as well as the complexity-entropy causality plane, and the chaotic nature of the instability fluctuations is identified. The frequency of the dominant fluctuations has been found according to the time scales corresponding to the extreme values of the symbolic quantifiers. The laminar-turbulent transition process is accompanied by the evolution in the degree of organization of the complex eddy motions, which is also characterized with the growing smaller and flatter circles in the complexity-entropy causality plane. With the help of the permutation entropy and the statistical complexity, the differences between the chaotic fluctuations detected in the experiments and the classical Tollmien-Schlichting wave are shown and discussed. It is also found that the chaotic features of the instability fluctuations can be approximated with a number of regular sine waves superimposed on the fluctuations of the undisturbed laminar boundary layer. This result is related to the physical mechanism in the generation of the instability fluctuations, which is the noise-induced chaos.