The effects of the double-wavelenght leading edge serrations on aerodynamic performance of the wing

Abstract

The negative effects of noise on the environment and living things are known to everyone. One of the sources of noise is aviation. So, noise reduction is a very important issue in aviation. Due to the effects of noise, there are many studies on noise reduction methods. Recent studies have focused especially on double-wavelength leading edge profiles designed as a combination of sine wave functions. When the studies in progress were examined, it was observed that the experiments were at a certain angle of attack and focused only on noise. In other words, the issue of how the aerodynamic performance of wings with such a design is affected in the majority of studies is not discussed, which is a situation considered to be missing in the literature. In this thesis, it is aimed to experimentally investigate how will be affected the aerodynamic performance of wings with double wavelength leading edge serrations, whose noise effect has been examined in the literature. In this context, an introduction has been made in the first part of the thesis that primarily focuses on why noise reduction is important. Then, where and how the noise occurs on the wings is explained. Following the examination of the noise source, the methods used from past to present to reduce the noise on the wings are imparted in detail. It is mentioned that the recent studies are serrations applied to the leading or trailing edges, and the studies on this subject are detailed. After providing detailed information about the study used as a reference in the content of the thesis, the motivation of the thesis is mentioned. In the second part of the thesis, the wing designs used in the experiments are mentioned. In this context, firstly, the two-dimensional shapes of the double wavelength leading edge serrations depending on the amplitude change are shown with the help of drawings and the design parameters are given as a table. Then, the three-dimensional designs of the wings created using the NACA 65-(12)10 airfoil were mentioned. At the same time, the situations that were taken into consideration during the wing drawings and that the wing was designed in two parts, front and rear, and that these parts could slide inside each other were mentioned. Three-dimensional drawings of the wings were made with the help of Solidworks program. By the way, it was also mentioned that due to the size limit in production, the wing was produced by dividing it into equal parts in the spanwise direction. The drawings prepared with the help of the program and then produced with a 3D printer and the surface roughness was eliminated. In addition to the double wavelength designs with two different amplitudes, a straight leading edge wing was also produced for comparison. So, in total there are 3 different wings. In the third part of the thesis, information about the experimental setup is given. Experiments in terms of aerodynamics were provided by the subsonic, open circuit wind tunnel in the Trisonic Research Laboratory within Istanbul Technical University. The speed at which the experiments were carried out, the placement of the wings in the tunnel and the angle of attack adjustment mechanism are also mentioned in this section. In addition, pressure measurement and flow visualization methods were mentioned. The placement of pressure taps on the wing for pressure measurement is explained visually. Additionally, brief information is given about the device used in the measurements. The tuft method was used during the flow visualization experiments, its features were briefly mentioned, and its application on the wings produced within the scope of the thesis was visually demonstrated. During the application of these methods, the angle of attack was also increased from low to high, and the effect of angle of attack was also examined. The experimental results are mentioned in the fourth chapter of the thesis. First, photographs obtained from flow imaging experiments were shown for each wing separately. Explanations were made with the help of images about the flow, whose behavior on the wing changes as the angle of attack changes. Following the results of the flow visualization experiments, the data obtained from the pressure measurements were presented graphically. Also shown is the comparison graph for the baseline wing. The graphs are non-dimensional and the pressure coefficient is used instead of pressure. To compare the wings with each other, the components perpendicular to the flow and parallel to the flow were calculated using the pressure coefficients obtained from the upper surface of the wing. The component perpendicular to the flow is called Cpl, and the component parallel to the flow is called Cpd. Using these data expressed in graphics, a comment was made about the aerodynamic performance of the wings relative to each other. In the conclusion part, the thesis was concluded by summarizing the data obtained from the experiments. According to the results of the experimental study conducted in this thesis, the pressure coefficients obtained from the upper surface of the wing and their perpendicular and parallel components to the flow have shown that the designed wings have better resistance to high angles of attack than the baseline wing. Among these two wings with double wavelength notched leading edges, it has been observed that this strength is better in the wing where the 2a value, expressed as the total amplitude, is smaller.