Browsing by Author "Hassan, Mohamed Ibren"

Gust load due to atmospheric turbulence is mandatory to be considered in the aircraft analysis as part of airworthiness requirement. The gust load alleviation plays an important role to effectively utilize the wing structural flexibility without ignoring the safety issue. In the present work, a method to alleviate the wing gust load is proposed by considering the structural flexibility of the wing and proper arrangement of composite material layers. The approach takes into account the wing planform, wing composite thickness and material direction, wing structural dynamic frequencies and modes, steady and unsteady aerodynamics of the wing surface. The objective of the study is to minimize the wing root bending moment power spectral density. The constraint of the study includes the wing material requirement, wing configuration, and the aerodynamic wing performance. The gust load analysis of the present structural model will be compared to the literature for the validation purpose. A finite element approach is used to simulate the wing structure in combination with the doublet lattice method to model the wing aerodynamics. The gust load profile, according to aviation regulations, is used. The proposed method gives a contribution to the gust load alleviation of large transport aircraft and unmanned air vehicles. It is clearly seen that the best configuration for reducing the bending moment power spectral density is swept back wing then swept forward. The swept-back configuration (45 degrees) showed an average decrease of the bending moment by 12% for a frequency range of 0 to 100 Hz. The present work also shows that the wing composite thickness and material direction affects the aerodynamic stability derivatives as function of Mach number which are important for the design of the aircraft flight dynamic and performance.

Low Reynolds number flow is three-dimensional and intricate due to multiple vortical phenomena. This research contributes by investigating the impact of laminar Separation Bubble (LSB) on noise generated by passive control techniques. It also enhances the understanding of the efficiency of various trailing edge designs such as serrations, comb, comb-serrated, and porous configurations, across different flow conditions and Reynolds numbers, while also addressing the limitations of existing geometrical models for trailing edges. The study intends to examine the performance of different configurations, emphasizing their effect on flow structure and acoustic responses. The methodology of this study encompasses a combination of techniques that includes conducting 2D simulations using the SST model, performing 3D simulations using large eddy simulation, employing FW-H acoustic modeling, and utilizing an experimental PIV setup. These methods collectively provide a comprehensive and robust platform for in-depth exploration of the research objectives. The analysis of the NACA0015 airfoil's flow characteristics revealed the presence of laminar separation bubbles (LSBs) at low Reynolds numbers and angles of attack. Two types of flow patterns, with and without reattachment, were identified. On the suction side, Increasing the Angle of attack leads to a noticeable upstream shift of these points, while they move downstream along the pressure side. In 3D simulations, pressure distribution was symmetrical, with the maximum at the leading edge. No separation was observed except at the trailing edge tip. At higher angles of attack, the baseline airfoil experienced flow disturbances, laminar separation bubbles, and vortex shedding. The serrated, combed, and comb-serrated designs exhibited more stable flow patterns and fewer separation bubbles than the baseline, potentially reducing tonal noise. Conversely, the poro-serrated design led to distorted flow and an upstream-moving separation bubble, suggesting a possible increase in tonal noise. Moreover, results showed irregular broadband noise (300 - 600 Hz) with increased noise and shifting peak frequency as the Angle of attack rose. The serrated trailing edge design notably reduced noise levels by roughly 21 dB, especially for low frequencies. Comb-serration increased high-frequency noise by about 9 dB for angles of attack at 0, -1, and -2 degrees reduced approximately 9 dB for angles of attack at 1 degree and 2 degrees. On the other hand, the directivity pattern showed that the maximum noise level is observed to predominantly radiate at an azimuth angle of around 90 degrees for all the cases, ranging from 90 to 270 degrees, indicating that the majority of the source's acoustic energy is being emitted on the suction and pressure sides of the wing. In conclusion, the findings demonstrate that serrated and comb-serrated designs are beneficial in reducing noise levels, and that the Angle of attack can significantly impact both the noise level and directivity pattern.