Experimental & Numerical Study Of Lift with Airfoil Diagram

Question: Describe about the Experimental and Numerical Study of Lift and Drag of an Airfoil. Answer: Introduction A number of research efforts have been inclined towards the airfoil drag and lift coefficients using a cross flow fan at varying boundary parameters by numerical and experiment means. Several experiments and numerical studies carried out reveal that many factors influence the value obtained for the drag and lift coefficients. As discussed in the paper, airfoil creates a great lift at lowest frontward velocities and reflects a great potential for both the scenarios of vertical landing and takeoff and that of quick landing and takeoff. Besides, the experimental results obtained reveal that the pitching moment and lift coefficients of the airfoil profile rise and the momentous drag coefficient declines as the rotational velocity of the airfoil fan declines. This means that in aeromechanics, the pitching moment constant improvement depicts that the aircraft gathers a relatively improved stability at comparatively superior rotational velocities. Significance of the Problem It is important to understand the parameters that govern the landing and takeoff of an aircraft in the modern aircraft mechanics and design. The study on drag and lift is crucial in aerodynamics today since it helps in understanding the pressure distribution on the airfoil profile. The information helps in the design of the airfoil fan and the determination of the appropriate pitching moment and the desired airfoil velocity. Literature Review Several researchers have undertaken to examine on the experimental and numerical study of drag and lift of an airfoil critically. Different researchers come up with different findings on the topic. To start with, Ã… ¾ahin and Acir (2015) of the Department of Energy Systems Engineering conducted an experiment at the Faculty of Technology, in the University of Gazi aimed at investigating the NACA 0015 transient dynamics, and carried out their measurements in an open wind tunnel. The parameters of the experiment were such that the wind velocity interval ranged between 3.1 and 28 m/s with an estimated cross-section of 30 cm by 30 cm m and a tunnel test of approximately 400 cm long. The diagram below shows the drag and lift of airfoil. As demonstrated in the figure, there are 4 major forces that act on the aircraft while in the air. In the case of a powered aircraft, there is a thrust force acting on the aircraft. The other forces operating on the aircraft include the weight of the aircraft, lift, and drag. However, the most important forces for analysis are drag and lift. The aircraft wing is the main contributor to the resultant drag and lift owing to the streamline shape of the airfoil. The streamline shape of the airfoil assists in providing great lift values at minimum drag for specified flight conditions. In addition, the wings of the conventional aircraft employ moving surfaces such as slats and flaps in most cases to adapt to the varying prevailing conditions. The other specifications of the NACA 0015 were 100 mm for both the spanwise length and the chord length. With a wind velocity of 10 meter per second and an attack angle in the range of 0 and 20 degrees, the experimental results showed that for an attack angle of 16 degrees, the highest drag and lift coefficients were 0.15 and 0.75 respectively. The optimum Cl/Cd ratio was registered at 8 degrees. The methods employed in estimating the non-dimensional coefficients were Drag coefficient . (1) (Askari Shojaeefard, 2012) Lift coefficient (2) (Dedeic, 2014) Where L is the lift, D is the drag, Cl is the lift coefficient, Cd is the drag coefficient, c is the chord length of the airfoil, V is the wind velocity, is the air density. The graphs below shows a comparison of the results obtained from this experiment with the numerical values. Figure 3Cl/Cd ratio for different attack angles Some important terms and concepts help in the determination of the lift and drag of the airfoil. In a more general sense, an airfoil has both a trailing edge and a leading edge that is basically designed with variant bottom and top surface curvatures to accelerate the flow that results from the induced pressure gradient generating a lift. The chord of the airfoil is the line that connects the trailing edge and the leading edge. In addition, a camber is the greatest distance covered between the chord and the surface of the airfoil as outlined in its profile. The airfoils chord length is the maximum length of the airfoil. Moreover, the attack angle of the airfoil is essentially the angle that is subtended between the relative fluid flow direction and the chord in a horizontal. Moreau, Jolibois, and Benard (2009) undertook a similar research using NACA 0015 airfoil model that was used by Ã… ¾ahin and Acir (2015) by mounting a Dielectric Barrier Discharge. In their experiment, they investigated the impact of both unsteady and steady drag and lift coefficient actuations using force measurements that were time-averaged. They found out that it is possible to delay the stall regime by 1 or 2 degrees while at the same time decreasing the drag coefficient. In order to investigate the stall flutter at minimum Reynolds numbers, Bhat and Govardhan (2013) conducted an experiment using a NACA 0012 airfoil model. The diagram below shows the wind blades of the wind turbine and the lift and drag. The flow fields and forces were measured by oscillating the airfoil at reduced Reynolds numbers of approximately 104. The airfoil underwent pitch oscillations with small amplitudes, , with great m known as angle of attack at varying frequencies, f. Energy transfer from the flow to the airfoil were computed by directly measuring the varying loads on the airfoil during oscillation. The researchers established that at low chord length (low Reynolds number), there was stall flutter and airfoil excitation. Wang, Ingham, Ma, Pourkashanian, and Tao (2010) also conducted a similar experiment using NACA 0012 model of airfoil by investigating the dynamic stall scenario in a 2D computational perspective at reduced Reynolds number of approximately 105. The researchers employed Computational Fluid Dynamics for the simulation with varying amplitudes, mean angles of oscillation, and frequencies in a two-set oscillating system. Dimchev (2012) conducted another study on the propellers mounted with wingtip with a UAV design and low aspect ratio. The study was conducted under a wind velocity ranging from 15 and 35 m/s and a 20 degrees proper blade angle. The results indicated that for a 10 degrees angle of attack, the there was an increase in the lift coefficient Cl from 0.34 to 0.46. On the contrary, there was a decrease of the drag coefficient Cd from -0.013 to -0.14. The figure below shows the flow profile of the drag and lift. Krogstad and Lund (2011) carried out a numerical and experimental analysis of a model turbine performance using a diameter of 90 cm for the model. The researchers used a S826 airfoil profile and used a Blade Element Theory to lay down the geometry. They then experimentally tested their design model and estimated the tip ratio at 6 and a peak power coefficient Cp at 0.448. A turbulence model known as - was used to undertake numerical calculations by applying a Computational Fluid Dynamics 3D simulation model. Evaluation and analysis of the findings From the literature analysis, it can be seen that the numerical and experimental results of the drug and lift of an airfoil vary depending on so many parameters. For instance, the experiments conducted under open tunnel as in the case of NACA 0015 reflect different values of the lift and drug constants. In addition, the area of cross section of the wind tunnel plays an imperative role in the value of the lift and drug coefficient obtained in an experimental setup. The other parameters that determine the value of the lift and drug coefficient include the velocity of the wind. Better results were obtained within the range of 20 and 30 m/s as the optimum wind speed. Moreover, the values obtained from the experiments indicate that an ideal attack angle averages at 16 degrees. The best experimental results obtained for the drag and lift coefficients vary between 0.15 and 0.75 respectively. In addition, the optimal Cl/Cd ratio that was recorded from the experiments is 8 degrees. The studies conducted by Tang, Zhang, Peng, and Liu (2012) suggest that airfoil develops a high lift at minimum forward velocities and demonstrates an exceptional potential for both the scenarios of upward takeoff and landing and that of fast takeoff and landing. As seen in most of the experiments, the pitching moment and lift constants of the airfoil rise and the resultant drag coefficient declines as the airfoil fan revolutionary velocity decreases. In aerodynamics, the pitching moment constant improvement shows that the aircraft achieves greater stability at elevated rotational velocities. Lombardi, Salvetti, and Pinelli, (2000) further highlight that experiments demonstrate that the streamline coefficients decline as the Reynolds number declines free stream. Besides, the flow area over the airfoil can best be been examined using the computational fluid dynamics approach and then comparing the results with the investigational results obtained. In most cases, the numerical results are in congruence with the values obtained in the experiments. Yu (2012) further establish that the rotational velocity of the airfoil does not affect the coefficient of skin resistance on the bottom wall of the airfoil. However, the upper surface of the foil, particularly the interior of the casing is greatly affected by the fan velocity. This also shows a rise in the Reynolds number on the two surfaces of the airfoil. Manolesos and Voutsinas (2016) cite that a close examination of the numerical method demonstrates that the difference between the inert pressure of the two airfoil surfaces lead to an increase in the rotational velocity. This leads to greater lift coefficients at a higher fan velocity, and a corresponding increase in the Reynolds number that corresponds to the improvement of the aeromechanic forces. Owing to the sharp edge of the airfoil, there occurs a dramatic abrupt jump in the pressure circulation on the upper region of the airfoil profile. When the sharp rim of the profile is replaced with a round and smooth profile, the pre ssure jump declines greatly and the resultant pressure distribution on the improved surface smoothens with a diminished extreme value (Norwazan, Khalid, Zulkiffli, Nadia, Fuad, 2012). The streamlines observed on the upper surface of the airfoil occurs at close proximity than the ones observed at the bottom of the airfoil. This indicates a greater pressure on the airfoils lower wall. The streamlines develops closeness on the upper area of the airfoil with an increase in the fan velocity. Additionally, the airfoil surface velocity gradient increases with increasing Reynolds number due to an elevated skin friction coefficient. Gao, Cai, Li, Jiang, and Lee (2016) and Ouchene, Khalij, Tanire, and Arcen (2015) cite that the incongruity that occurs between the experimental and numerical values are due to uncertainty in the experimental measurements and the convergence exactitude that occurs in the numerical approach. Furthermore, there is the reality of the 3D dimensional profile of the f low that is different from the theoretical 2D solution in the computational fluid dynamics (Haryanto, Utomo, Sinaga, Rosalia, Putra, 2014). Conclusion From the experiments and numerical analyses carried out, several factors determine the value of the lift and drag coefficients obtained. As observed in the paper, airfoil develops a great lift at minimum frontward velocities and evidences an outstanding potential for both the backdrops of vertical landing and takeoff and that of fast landing and takeoff. Also, as observed in the experimental results, the pitching moment and lift constants of the airfoil elevates and the consequential drag coefficient downslopes as the revolutionary velocity of the airfoil fan diminishes. In aeromechanics, the pitching moment constant improvement reflects that the aircraft attains a relatively better stability at superior rotational velocities. Additionally, experiments reflect that the streamline coefficients decay as the Reynolds number reduces for the free stream. Moreover, the field of flow above the airfoil can most excellently be observed using the computational fluid dynamics method and then dr awing parallels of the results with the experimental values realized. 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