Vortex dynamic investigation of wing slotted gap of SAAB JAS Gripen C-like fighter

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This study investigated the vortex dynamic of wing canard delta configurations of the Saab JAS Gripen C-like model which create different wing planform than other fighters.

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International Journal of Mechanical Engineering and Technology (IJMET) Volume 10, Issue 03, March 2019, pp. 567-575. Article ID: IJMET_10_03_058 Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=3 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 © IAEME Publication Scopus Indexed VORTEX DYNAMIC INVESTIGATION OF WING SLOTTED GAP OF SAAB JAS GRIPEN C-LIKE FIGHTER Sutrisno Department of Mechanical and Industrial Engineering, Faculty of Engineering, Universitas Gadjah Mada, Yogyakarta, Indonesia 55281 Setyawan Bekti Wibowo Department of Mechanical and Industrial Engineering, Faculty of Engineering, Universitas Gadjah Mada, Yogyakarta, Indonesia 55281 Sigit Iswahyudi Department of Mechanical and Industrial Engineering, Faculty of Engineering, Universitas Gadjah Mada, Yogyakarta, Indonesia 55281 Department of Mechanical Engineering, Faculty of Engineering, Universitas Tidar, Magelang, Indonesia 56116 Tri Agung Rohmat Department of Mechanical and Industrial Engineering, Faculty of Engineering, Universitas Gadjah Mada, Yogyakarta, Indonesia 55281, ABSTRACT Canard fighters generally configured with wing canard-deltas and would generate an airflow phenomenon producing vortex cores and lifts. The lift distribution would stall at a high angle of attack (AoA). This study investigated the vortex dynamic of wing canard delta configurations of the Saab JAS Gripen C-like model which create different wing planform than other fighters. The slotted leading edge of the Gripen would develop a strong vortex core on the outer wing, on the same direction with the spin of wing vortex; the outer core would drag the inner vortex core and strengthened. Consequently, the vortex core streamlined in a leading edge of the wing would begin to detach, resulting rolled-up vortices in the wing leading edge followed by a solid laminar stream which tends to curl out. The trailing edge of the wing tended to laminarize backward. The result would be a negative surface pressure on the leading edge above the canard and on the wing which causes more negative surface pressures. An increase in AoA will generate a closer vortex breakdown location to the wing leading edge. The location was calculated as the ratio of the axial velocity value to http://www.iaeme.com/IJMET/index.asp 567 editor@iaeme.com
Vortex Dynamic Investigation of Wing Slotted Gap of Saab Jas Gripen C-Like Fighter free velocity (U/U∞) at a value of 0.1. As the AoA increased, the vortex breakdown location moved forwards, upwards, and moved away from the fuselage. Keywords : slotted leading edge, outer vortex core, high AoA, laminarize backward. Cite this Article Sutrisno, Setyawan Bekti Wibowo, Sigit Iswahyudi and Tri Agung Rohmat, Vortex Dynamic Investigation of Wing Slotted Gap of Saab Jas Gripen C- Like Fighter, International Journal of Mechanical Engineering and Technology, 10(3), 2019, pp. 567-575. http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&IType=3 1. INTRODUCTION The delta wing study with computational processes generally uses the κ-ω turbulent model. The reason is that using a turbulent Shear Stress Transport (SST) κ-ω model will predict high accuracy flow separation, as the most appropriate choice for delta wing flow [1]–[3]. This CFD simulation was strengthened by mesh independence test [4]. Zhang et al. have numerically investigated the canard-forward swept aircraft focusing on interference between canard and wings [5]. Simulation of numerical fighter F-16XL models for geometry and computational grids with structured and unstructured grids have also been carried out using delayed detached-eddy simulations, as well as on flight conditions using fluid dynamics computational near-body CFD / off body hybrid [6]–[8]. Several prominent scientists have investigated several fighters. Boelens has modeled CFD flow around the X-31 fighter at high AoA [9]. Chen et al. have explored the sideslip effect of high AoA vortex flow in close pair canard configuration [10]. Ghoreyshi et al. have validated the simulation of Canard TransCruiser's static and forced flow of motion [11]. Ghoreyshi et al. have modeled the transonic aerodynamic load of pitching X-31 aircraft [12]. Schütte and Rein have examined numerically and experimentally unstable simulations around X-31 [13]. The purpose of this paper is to analyze the vortex dynamics of the SAAB JAS Gripen C- like aircraft model in terms of performance, visualization of flowline above the canard and wing, streamlined visualization above the canard and wing, streamline above the limiting wall shear streamline on aircraft surface, wall-pressure distribution as well as pressure and surface breakdown location. By knowing the characteristics of the dynamic vortex of the SAAB JAS Gripen C-like aircraft model one can identify its excellence and find suggestions for improvements that might be sought and improved further towards improving performance and achievement. 2. RESEARCH METHODS The model observed in this research was the SAAB JAS Gripen C-Like fighter model, as shown in Figure 1, with several simplifications in symmetrical models, and several detailed images, such as antennas. In this research, nets on fighter planes were made by identifying parts of the plane and then dividing them into several blocks based on changes in the plane's surface. Hexahedral nets were arranged by changing the size of the net, starting from the part of the wall as the smallest size and enlarging logarithmic to the outside [8]. The optimal number of cells was obtained by conducting a mesh independence test, as shown in Table 1. The previous test with 5 million cells, had reached a convergence of lift strength coefficient values. In the case of this model, the number of cells made was 6,012,908 (~ 6 million). To determine the smallest mesh size on the wall, the y+ value was 4, with the lowest cell value 0.017 mm. Dogfighting of the fighter was conducted at slow speeds, i.e. at 0.3 M. When a Mach number was at a higher value, it caused drag divergence. This was caused by the shock waves http://www.iaeme.com/IJMET/index.asp 568 editor@iaeme.com
Sutrisno, Setyawan Bekti Wibowo, Sigit Iswahyudi and Tri Agung Rohmat formation at the upper surface of the airfoil, causing flow separation and an adverse pressure gradient on the back of the wing. Thus the vortex dynamics pattern around the fighter would be symmetrical, and the calculation was done by a half model to save time. Figure 2 displays the net and the grid shape above the canard. The computational domain was square with half a symmetrical model. The boundary conditions in the computational domain were determined, including the inlet or speed inlet, outlet or pressure outlet, and the symmetrical plane. Table 1 Mesh independent test for different cell number [14] Criteria AoA Cl Error Boelens, 2012 300 1.02157 1.3 million grids 300 1.074078 5.14% 3.1 million grids 300 1.042085 2.01% 5.2 million grids 300 1.026022 0.44% This study involved several variations of the AoA ranging from 200 to 700. The flow rate was set at an inlet velocity of 0.3 M (114. m/s) flowing on the surface of the plane with a 0.08% turbulence intensity. The flow analysis employed the finite volume method based on the Navier-Stokes equation. (a) (b) Figure 1 Geometrical model (a) SAAB JAS Gripen C-like (b) computational domain structure (modified [14]). http://www.iaeme.com/IJMET/index.asp 569 editor@iaeme.com
Vortex Dynamic Investigation of Wing Slotted Gap of Saab Jas Gripen C-Like Fighter Figure 2 Structured grid SAAB JAS Gripen C like. Vortex dynamics analysis was used to analyze the fuselage and RuV effects of the Gripen- like fighter canard [15]. Vortex dynamics analysis involved flow visualization to analyze fighters and a review of the measurement results. The flow visualization plot of the primary vortex center was also presented, which may also generate the second vortex center. Afterward, the measurement results were analyzed. 3. RESULT AND DISCUSSION 3.1. Performance Figure 3 Distribution curve of CFD simulation of CL, CD and CL/CD of SAAB JAS Gripen C-like aircraft The simulation results in the form of CL, CD, and lifts to drag ratio was shown in Figure 3. In Figure 3, the CL of a) SAAB JAS Gripen C-like aircraft became higher and b) the distribution curve of CD simulation of SAAB JAS Gripen C-like aircraft were exposed. http://www.iaeme.com/IJMET/index.asp 570 editor@iaeme.com
Sutrisno, Setyawan Bekti Wibowo, Sigit Iswahyudi and Tri Agung Rohmat 3.2. Streamline simulation on canard and wing at AoA 100, 200, 300 and 600 In Figure 4 displayed flow pathline speed of 102,9 m/s at AoA variation 300 and 600. In the beginning, swirling flow pathlines described two vortex cores. Figure 4.a described a flow pathline as well as a picture of the vortex core above the canard on AoA 100, along with a picture of the vortex core above the wing. (a) (b) (c) (d) Figure 4 Streamline visualization/ flow pathline above the canard and the wing at AoA a) 100, b) 200, c) 300 and d) 600. It appeared that the vortex core above the canard started dragging the vortex core above the wing. Figure 4.b and c illustrated the vortex cores, above the canard from the canard and above the wing began to coalesce became one core, gave strong drag on the vortex core in the leading edge of the wing so that it started to release. In Figure 4.b and c, the rolled-up vortex from the vortex core in leading edge wing started to release and to weaken, so that the laminar flow behind it tended to weaken. The appearance in Figure 4.b and c showed the effect of the slotted leading edge gave rise to a strong vortex core that dragged strong vortex core with the direction getting stronger but tend to escape after the leading edge. 3.3. Limiting streamline on the aircraft surface above the wing at AoA 300 and 600. In Figure 5.a and b one could see the wall-shear-streamlines above the wing at AoA 300 and 600. In Figure 5.a one could see the limiting streamline above canard flows laminar, as a result of the flow path line in Figure 5.a flow over the canard tend to curl out, as well as above the wing at the end of the leading edge tends to rolled up and behind it tends to laminate curved out, with the trailing edge tends to be laminar straight backward. Whereas the streamlined http://www.iaeme.com/IJMET/index.asp 571 editor@iaeme.com
Vortex Dynamic Investigation of Wing Slotted Gap of Saab Jas Gripen C-Like Fighter effect in Figure 5.b shown at the leading edge of the strong vortex core which tends to begin to detach behind it, resulting in the rolled-up vortex in the wing leading edge followed by the laminar flow which tends to curl out solidly, and on the trailing edge the wing tend to laminate backward. (a) (b) Figure 5 Wall shear streamlines above the wing at AoA a) 300 and b) 600. 3.4. Surface pressure contour at AoA 200, 300, 400, 600 and vortex breakdown location of the Gripen fighter Figure 6 displays the wall-pressure distribution above the wing at AoA a) 200, b) 300, c) 400 and d) 600 of the SAAB JAS Gripen C-like aircraft (a) (b) (c) (d) Figure 6 Wall-pressure distribution above the wing at AoA a) 100, b) 200, c) 300 and d) 600. http://www.iaeme.com/IJMET/index.asp 572 editor@iaeme.com
Sutrisno, Setyawan Bekti Wibowo, Sigit Iswahyudi and Tri Agung Rohmat In this study at V = 102.9 m/s, at AoA 400 it measured CL = 1.44. In Figure 6.a above the canard, it described the negative surface pressure at the leading edge. Moreover, above the wing, the surface pressure was more negative and reached the negative pressure maximum = - 2.05x104 Pa. Furthermore, as AoA increased, negative surface pressure also increased, as shown in Figure 6 b) AoA 200, c) AoA 300 and d) AoA 600. The increase in the AoA would result in the vortex breakdown location approaching the leading edge of the wing as shown in Figure 7. The location of the vortex breakdown is identified from the ratio of the axial velocity to free velocity (U / U∞) at the value 0.1. 1.2 1 0.8 (x/C) 0.6 0.4 0.2 0 0 10 20 30 40 50 60 70 80 Angle of attack (degree) Figure 7 Vortex breakdown location against AoA 3.5. Comparison with previous studies In the following are shown some of the results of previous studies compared to the results of the SAAB JAS Gripen C-like aircraft research. Compared to the Sukhoi Su-47 [16], the Su- 47 has a higher lift-to-drag ratio, greater air battle maneuvering capacity, higher range at subsonic speeds. By the Sukhoi Su-30 research in water tunnel [17], the study emphasized the increase in the maximum coefficient of lift due to the effect of the aircraft body. Compared with the results of the Sukhoi Su-30 [14] canard deflection effect of Su-30 was lifted optimization on high AoA. The maximum CL value of Eurofighter [18], Chengdu J-10 from CFD computation [19] and water tunnel measurement [20] is lower than the Gripen fighter. 4. CONCLUSION From the research of SAAB JAS Grip-C-like aircraft, it was found that the slotted leading edge of the Gripen caused a strong vortex core and therefore additional pointy tip produced two vortex cores, namely ordinary inner rolled-up vortices in the inner wing leading edge and outer rolled-up wing leading edge of the slotted gap. Rolled-up vortex cores due to slotted gaps in the inner rolled-up vortex cores began to coalesce to become one stronger vortex core, which dragged the inner vortex core in the wing leading edge. As a result, the CL of SAAB JAS Gripen C-like aircraft became higher. Flow over the canard tend to curl out, as well as above the wing at the end of the leading edge tends to roll- up and behind it tends to laminate curved out, with the trailing edge tends to be laminar http://www.iaeme.com/IJMET/index.asp 573 editor@iaeme.com
Vortex Dynamic Investigation of Wing Slotted Gap of Saab Jas Gripen C-Like Fighter straight backward. As AoA increased, negative surface pressure also increased, and the vortex breakdown location approaching the leading edge of the wing. The trend of the vortex core length is getting shorter with the increase of AoA as denoted by the vortex breakdown location. As the AoA increased, it started to release energy and weakening and will increase the vortex breakdown location closer to the wing leading edge. As the AoA increased, the vortex tends to detach in the wing leading edge, resulting rolled-up vortices in the wing leading edge. On the trailing edge the wing tends to laminarize backward. The result is a negative surface pressure on the leading edge above the canard and the wing more negative. ACKNOWLEDGMENTS The authors would like to express heartfelt gratitude to Dr. Bramantyo for a fruitful session, useful suggestions, and collaboration. We appreciate the help of our students Wega, David, Patricius, and Yogi, and the lab staff members, Ponimin and Wajiono, for giving their help in construction work and conducting data management, which we gratefully acknowledged. This study was funded by the Government of the Republic of Indonesia Department of Research Technology and Higher Education, PTUPT-2018, under the contract 1859/UN1/DITLIT/DIT- LIT/LT/2018 NOMENCLATURE vα = angle of attacks (AoA/deg) y+ = dimensionless wall distance CL = lift coefficient CD = drag coefficient M = Mach number P = total pressure loss (Pa) Uc = axial canard vortex centre velocity (m/s) U∞ = free stream velocity (m/s) VBD = vortex breakdown location REFERENCES [1] Subagyo, “Numerical simulation of unsteady viscous flow around airship using vortex method,” J. Teknol. Dirgant. Vol. 8 No. 2 Desember 2010125-135 unsteady, vol. 8, pp. 125–135, 2010. [2] S. Saha and B. Majumdar, “Flow visualization and CFD simulation on 65° delta wing at subsonic condition,” Procedia Eng., vol. 38, pp. 3086–3096, 2012. [3] B. Soemarwoto and O. Boelens, “Simulation of vortical flow over a slender delta wing experiencing vortex breakdown,” AIAA Pap., pp. 7–16, 2003. [4] S. Wibowo, S. Sutrisno, and T. Rohmat, “Study of Mesh Independence on the Computational Model of the Roll-up Vortex Phenomena on Fighter and Delta Wing Model,” Int. J. Fluid Mech. Res., vol. 46, no. 2, p. in press, 2018. [5] G. Q. Zhang, S. C. M. Yu, A. Chien, L. Angeles, and S. X. Yang, “Aerodynamic Characteristics of Canard-Forward Swept Wing Aircraft Configurations,” J. Aircr., vol. 50, no. 2, pp. 378–387, 2013. [6] O. J. Boelens et al., “F16-XL Geometry and Computational Grids Used in Cranked-Arrow Wing Aerodynamics Project International,” J. Aircr., vol. 46, no. 2, pp. 369–376, 2009. http://www.iaeme.com/IJMET/index.asp 574 editor@iaeme.com
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