AEROTECH V: Progressive Aerospace Research

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Authors: Siti Nur Aishah Mohd Haris, Mohamed Sukri Mat Ali, Sheikh Ahmad Zaki Shaikh Salim, Sallehuddin Muhamad, Muhammad Iyas Mahzan
Abstract: The Lighthill acoustic analogy is applied to estimate the noise radiation from flow over a blunt trailing edge. The blunt trailing edge is an effective vortex generator. Periodic vortex shedding near the trailing edge induces fluctuating lift that radiates a strong Aeolian tone. The frequency of the Aeolian tone is similar to that of the vortex shedding. A 50.1 dB of Aeolian tone level is radiated from this blunt trailing edge.
Authors: Harijono Djojodihardjo, Muhammad Anas Abd Bari, Azmin Shakrine Mohd Rafie, Surjatin Wiriadidjaja

The basis of this work was to understand the generation of lift and thrust of a flapping bi-wing ornithopter, which is influenced by its geometrical, dynamic, kinematic and aerodynamic features by following a generic approach in order to identify and mimic the mechanisms. As further development of earlier work, three-dimensional rigid thin wing is considered in flapping and pitching motion using strip theory and two-dimensional unsteady aerodynamics for idealized wing in pitching and flapping oscillations with phase lag. Later, parametric study is carried out to attain a complete cycle’s lift and thrust physical characteristics for evaluating the plausibility of the aerodynamic model and for the synthesis of an ornithopter model with simplified mechanism. Further investigation is conducted to identify individual contribution of generic motion towards the flight forces. Results are assessed in comparison with existing theoretical and experimental results as appropriate.

Authors: Hamid Yusoff, Mohd Zulkifly Abdullah, Kamarul Arifin Ahmad, M.K. Abdullah, Shafiq Suhaimi
Abstract: In the present study, the aerodynamic characteristics such as time-averaged lift and drag generation of two flexible membrane (latex thin and thick) wings with different skin flexibilities are compared with those of a conventional rigid (wood) wing to assess the effects of skin flexibility (rigidity) on the aerodynamic performance for flapping flight applications. The experiments are performed in an open circuit wind tunnel of non-return airflow with a test section of (0.3m x 0.3m) and is capable of speeds from 0.5 to 30 m/s. The time-averaged lift and drag as functions of flapping frequency, forward flight velocity and the orientation angle of the flapping motions with respect to the incoming flows are measured by using a strain gauge balance and KYOWA PCD-300A sensor interface data acquisition system. It has been found that flapping motion would bring significant aerodynamic benefits when the flapping flight is in unsteady state regime, with advance ratio less than 1.0. The aerodynamic benefits are found to decay exponentially with the increasing advance ratio. Flapping motion is found to become detrimental for high speed flight applications. It is also observed that the skin flexibility has considerable effect on the aerodynamic performance. The flexible latex thick wing is found to have better overall aerodynamic performance over the rigid wing, especially for low speed applications. The wood (rigid) wing exhibited better lift production performance in quasi steady regime.
Authors: Hussain H. Al-Kayiem
Abstract: Experimental details of the flow field and wake over airfoils and 2-D wings are time and cost consumption. In this study, the flow visualization technique was adopted to investigate the flow field surrounding NACA4412 airfoil. The investigations were carried out in smoke tunnel, operating at low Reynolds number in a range of 105. The airfoil was tested in two operational cases: first as clean wing and the second as under-loaded wing by attached missile model. The experiments were conducted at various angles of attack as 00, 50,100, 150 and 200. It was found that the under-load of external body under the wing is influencing the flow structure over the wing. Also, the wake after the external body is swirling, leading to very complicated wake interaction. The results from the work can support the numerical simulation and the prediction of the laminar to turbulent transition and the separation and wake interaction of high lift airfoil flow fields.
Authors: Syed Mohammed Aminuddin Aftab, Kamarul Arifin Ahmad
Abstract: In this work, the characteristic design of the humpback whale flippers is incorporated and investigated on NACA 4415 airfoil at very low Mach number. The effect of Tubercle Leading Edge on NACA4415 airfoil has been studied. This novel study attempts to mimic the effect of tubercles on the airfoil wing to improve lift and delay stall. The results showed significant improvement in aerodynamic performance of TLE when compared to CW. TLE, in comparison to wing with vortex generators, performed better. An improvement in lift by about 13.6% was obtained contrary to only 6.3% increase in case of VG under same Reynolds number. In addition, it was also observed that incorporation of tubercles further delayed stall and continued to produce lift at high angle of attacks.
Authors: Anwar Ul Haque, Waqar Asrar, Ashraf Ali Omar, Erwin Sulaeman, J.S. Mohamed Ali
Abstract: Use of low fidelity tools in designing subscale generic wind tunnel models is usually required to get first-hand knowledge about general trends of aerodynamic and stability parameters. Most of such tools are limited to well-defined conventional aircraft configurations. In the present work, aerodynamic and stability characteristics of a winged hybrid airship is explored at low subsonic speed by using Aircraft Digital DATCOM, which is based on semi-empirical methods for preliminary aircraft geometries. Spheroidal ellipsoidal shaped hull of the airship is modeled in DATCOM along with the geometrical details of wing and empennages. The prediction of zero lift drag coefficient, coefficient of lift and pitching moment is the focus of this paper. Except the drag coefficients, trends of analytical results compare well with experimental data.
Authors: Baramee Wessapakdee, Pranchalee Makarasut, Chinnapat Thipyopas
Abstract: This project is designed to find out a proper shape for the Coanda effect and use them for helping a vertical takeoff vehicle to create additional lift. Experiment and numerical calculations were conducted. The model was set up by placing a propeller at 10 cm above the surface. Shape, height and model with a hold at the center were investigated by ANSYS Fluent. Propeller was simulated by applying actuator disk. First shape is a semi sphere with 50 cm diameter. Second, surface in invert parabolic shape with 50 cm diameter with varying height 15, 25 and 35 cm are considered. The last shape is similar to the second case with 15 and 35 cm height, but it is made hollow by varying the hold's diameter as 7, 11 and 15 cm. The total number of the entire cases is 10. The result shows that the best shape for the Coanda effect is a semi sphere shape but total lift of all models without a hole in the middle, in the first and the second cases, are negative and tend to decline when the height of the shape increases. For the third case, the shape with a height of 35 cm and 15 cm hold diameter has the least negative lift.
Authors: Matthew James Marino, Simon Watkins, Roberto Sabatini, Alessandro Gardi
Abstract: Experiments at low Reynolds numbers were performed on a pressure tapped NACA 2313 wing in a 3 x 2 x 9 meter wind tunnel under nominally smooth (Ti = 1.2%) and turbulent (Ti = 7.2%) flows at a mean flow velocity of 8ms-1 (Re ≈120,000). The NACA 2313 wing is a replica of Micro Air Vehicle (MAV) wing of the Flash 3D aircraft used at RMIT University for research purposes. Unsteady surface pressures were measured to understand if the information could be adopted for resolving turbulence-induced perturbations and to furthermore use it in a turbulence mitigation system. Two span-wise locations of chord-wise pressure were acquired when tested under the two different flow conditions. It was discovered that at both span-wise locations, a local Coefficient of Pressure (Cp) held high correlation to the chord-wise Cp integration and allowed for a linear relationship to be formed between the two variables. The defined relationship provided a 95% confidence for angles of attack below stall and was used to estimate the integrated chord-wise pressure coefficient at a particular span wise location. The relationship between a single pressure tap and the integrated Cp of that chord-wise section was valid for the two different span-wise locations with similar defining equations. As one pressure tap is sufficient to adequately estimate the integrated Cp on a chord-wise wing section, a limited amount of pressure taps across the wings span approximates the pressure distribution across the span and eventually approximates the flight perturbations. Being a novel method of sensing aircraft disturbance, applications are not restricted to MAV. The methodology presented could very well be applied to larger aircraft to reduce the effects of turbulence within the terminal area and can provide other means of active stabilization.
Authors: Al Emran Ismail
Abstract: The solution of stress intensity factor (SIF) for central edge crack embedded in bi-material plate can be found in open literature. Instead of a single edge crack, some researches on the multiple crack problems can also be found. However, the solutions of SIFs for multiple edge cracks in bi-material plates are difficult to obtain. In this paper, such problems are solved numerically using ANSYS finite element program. There are three important parameters that are used namely, relative crack depth, a/W, relative offset distance, b/h and modulus ratio, E1/E2. Both materials are assumed to be perfectly bonded and fulfill the plain strain condition. It is found that all variables used play an important role in determining the SIFs. However, when b/h is large enough, it has no significant effect on the SIF where it converged to an almost single value. The same situation does not occur for mode II SUFs where the SIFs diverged when the parameters used are increased.

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