Purpose The purpose of this paper is to mount Gurney flaps at the trailing edges of the canards and investigate their influence on aerodynamic characteristics of a simplified canard-configuration aircraft model. Design/methodology/approach A force measurement experiment was conducted in a low-speed wind tunnel. Hence, the height and shape effects of the Gurney flaps on the canards were investigated. Findings Gurney flaps can increase the lift and pitching-up moment for the aircraft model tested, thereby increasing the lift when trimming the aircraft. The dominant parameter to influence aerodynamic characteristics is the height of Gurney flaps. When the flap heights are the same, the aerodynamic efficiency of the triangular Gurney flaps is higher than that of the rectangular ones. Moreover, the canard deflection efficiency will be reduced with Gurney flaps equipped, but the total aerodynamic increment is considerable. Practical implications This paper helps to solve the key technical problem of increasing take-off and landing lift coefficients, thus improving the aerodynamic performance of the canard-configuration aircraft. Originality/value This paper recommends to adopt triangular Gurney flaps with the height of 3 per cent chord length of the canard root ( c ) for engineering application.
The frequency response model for the underwater wireless optical communication channel is obtained using the discrete ordinates method based on vector radiative transfer theory. And the performance of a 1Gb/s communication system with M-ary PPM has been evaluated by applying this frequency response model. The results show that with the increase of transmission distance the bit-error-rate performance degrades, and the field of view (FOV) has a different behaviour in terms of bit-error-rate performance as distance increases. In short distance, with the increase of FOV the bit-error-rate performance degrades, and in long distance, it is opposite. The 4-PPM bit-error-rate performance is almost equal to that of OOK modulation. 8-PPM or 16-PPM can be used to get more improvement in bit-error-rate performance and higher power efficiency.
The low-speed wind tunnel experiment is carried out on a simplified aircraft model to explore the influence of wing flexibility on the aircraft aerodynamic performance. The investigation involves the measurements of force, membrane deformation and velocity field at Reynolds number of 5.4 × 104–1.1 × 105. In the lift curves, two peaks are observed. The first peak, corresponding to the stall, is sensitive to the wing flexibility much more than the second peak, which nearly keeps constant. For the optimal case, in comparison with the rigid wing model, the delayed stall of nearly 5° is achieved, and the relative lift increment is about 90%. It is revealed that the lift enhanced region corresponds to the larger deformation and stronger vibration, which leads to stronger flow mixing near the flexible wing surface. Thereby, the leading-edge separation is suppressed, and the aerodynamic performance is improved significantly. Furthermore, the effects of sweep angle and Reynolds number on the aerodynamic characteristics of flexible wing are also presented.
The kinematic characteristics of flexible membrane wing have vital influences on its aerodynamic characteristics. To deeply explore the regularities between them, time-resolved aerodynamic forces and deformations at different aeroelastic parameters and angles of attack (α) were measured synchronously by wind tunnel experiments. The membrane motion can be mainly divided into two states at α > 0° with various lift-enhancement regularities: Deformed-Steady State (DSS) at pre-stall, and Dynamic Balance State (DBS) at around stall and post-stall. Besides, the mean camber, maximum vibration amplitude, and lift coefficient almost reach their maxima simultaneously within the DBS region. By introducing momentum coefficient Cμ of membrane vibration, positive correlation among amplitude, momentum and lift is successfully established, and the lift-enhancement mechanism of membrane vibration is revealed. Moreover, it is newly and surprisingly found that at different vibration modes, the maximum vibration amplitude and root mean square of vibration velocity present positive and linear correlation with different slopes, and their chordwise locations are basically consistent. Therefore, novel ideas for active control of flexible wing are proposed: by controlling the vibration amplitude, frequency, and mode, while selecting the specific chordwise locations for intensive excitation, Cμ can be efficiently increased. Ultimately, the aerodynamic performance will be improved.
In order to improve the classification performance of Polarimetric Synthetic Aperture Radar (PolSAR) image by synthesizing various polarimetric features, a supervised manifold learning method is proposed in this paper for PolSAR feature extraction and classification.Under the umbrella of tensor algebra, the proposed method characterizes each pixel with a feature tensor by combining the high-dimensional feature information of all the pixels within its local neighborhood.The tensor representation mode integrates the polarimetric information and spatial information, which is beneficial for alleviating the influence of speckle noise.Then, the tensor discriminative locality alignment (TDLA) method is introduced to seek the multilinear transformation from the original polarimetricspatial feature tensor to the low-dimensional feature.The label information of training samples is utilized during feature transformation and feature mapping; therefore, the discriminability of different classes can be well preserved.Based on the extracted features in the low-dimensional space, the SVM classifier is applied to achieve the final classification result.The experiments implemented on two real PolSAR data sets verify that the proposed method can extract the features with better stability and separability, and obtain superior classification results compared to several state-of-the-art methods.
Fluid–structure interaction of a flexible membrane wing was investigated experimentally at a fixed angle of attack (α = 14°). The Reynolds numbers (Re) based on the chord length of the membrane wing were 6 × 104, 6.6 × 104, and 8 × 104, respectively, which belong to low Reynolds numbers. Membrane deformations and the global flow fields around the membrane wing were measured synchronously with two-dimensional time-resolved particle image velocimetry. The membrane performs strongly periodic standing-wave vibration modes while interacting with the surrounding flow. Although the flow fields and membrane vibrations are coupled in all Re cases, it is newly discovered that, at Re = 6 × 104, the dominant frequency of the flow is around 9.1 Hz (Strouhal number St = 0.15) instead of the dominant membrane vibration frequency of 35.1 Hz (first-order vibration mode, St = 0.56). By tracking the Lagrangian coherent structures over the membrane, it is revealed that the vortical structures at Re = 6 × 104 are affected by the flow from both the leading- and trailing-edges. The frequency of 35.1 Hz in the power spectrum of flow is attributed to the successive shedding of leading-edge vortices coupled with membrane vibration, while the dominant frequency of flow field (9.1 Hz) is resulted from the interaction of strong trailing-edge reverse flow and the leading-edge separated flow, and the mechanism is explored. For higher Re cases (Re = 6.6 × 104 and 8 × 104), the membrane presents second- and third-order vibration modes separately. The dominant frequencies of the flow structure and membrane vibration are consistent, and the periodic shedding of leading-edge vortices is the main flow characteristic in both Re cases.
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