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An experimental study on examining aerodynamic characteristics of fuselage cross sections for RLVs (Reusable Launch Vehicles) was conducted at Mach number 0.3, 0.9 and 4.0 in the wind tunnel of ISAS (Institute of Space and Astronautical Science), JAXA (Japan Aerospace Exploration Agency). Three bodies, having the same projected area and length, with and without a set of fins, were tested. Their cross sections are a circle, a square and a triangle with rounded corners. The results showed that the fuselage cross sections had large effects on aerodynamic characteristics in subsonic and transonic flow. The lift coefficient of the model having the triangular cross section with a set of the fins was larger than that of the others in high angles of attack region due to contributions of the separation vortices generated from the fuselage expanding to the wing surface.

Space transportation system is one of the most important infrastructures for space activities. Low cost, improvement of reliability and safety are required for the development of RLV (Reusable Launch Vehicle). To achieve high aerodynamic performance in the whole flight speed region is one of the most important issues in the development of RLV. High lift performance at low speed regime makes possible a shorter landing distance, and high lift-to-drag ratio performance allows easy approach during landing process, larger down and cross range in high speed region.

Such RLVs have larger aerodynamic effects on a fuselage configuration due to a larger fuselage cross section compared with that of aircrafts. Therefore, investigating a favorable fuselage configuration of the RLVs is important to enhance the aerodynamic performances.

Examples of past studies [

Therefore, the purpose of this study is to identify aerodynamic effects due to different fuselage configurations to enhance aerodynamic performance for RLV. In this paper, we report experimental results by using three fuselage cross sections, such as a circle, a triangle and a square, having that same projected area and length, with and without a set of fins at M_{∞} = 0.3, 0.9 and 4.0.

The experiments were carried out in the transonic wind tunnel, supersonic wind tunnels of ISAS, JAXA and in the low speed wind tunnel of Kyushu University. Both the transonic and supersonic tunnels are blow-down type facility. Each operating Mach numbers is from 0.3 to 1.3 and from 1.3 to 4.0, respectively. The size of test section is 600 mm width, 600 mm height. The low speed wind tunnel of Kyushu University has a closed circuit and an open test section which diameter of nozzle exit is 2,000 mm. The max speed is 21 m/s.

^{2} and a same length, 0.3448 m. As shown in

^{2}, used as a reference area. The wings of these models have a delta planform of modified NACA0010 cross section with 45 degree sweepback angle, referred to past studies [

The full length is 0.3448 m, used as a reference length. Center of the balance in all models is located at 231 mm behind from the front nose edge of the models. A sting-type six-component internal balance was used for the measurement of forces and moments.

M_{∞} | Model | α (deg.) | Re |
---|---|---|---|

0.3 | Circle | −15 ~ 40 | 3.1 × 10^{6} |

0.3 | Square | −15 ~ 40 | 3.1 × 10^{6} |

0.3 | Triangle | −15 ~ 40 | 3.1 × 10^{6} |

0.3 | Square with wings | −15 ~ 40 | 3.1 × 10^{6} |

0.3 | Triangle with wings | −15 ~ 40 | 3.1 × 10^{6} |

0.9 | Circle | −15 ~ 40 | 7.3 × 10^{6} |

0.9 | Square | −15 ~ 40 | 7.3 × 10^{6} |

0.9 | Triangle | −15 ~ 40 | 7.3 × 10^{6} |

0.9 | Square with wings | −15 ~ 35 | 7.4 × 10^{6} |

0.9 | Triangle with wings | −15 ~ 32.5 | 7.3 × 10^{6} |

4.0 | Square with wings | −15 ~ 40 | 8.2 × 10^{6} |

4.0 | Triangle with wings | −15 ~ 40 | 8.2 × 10^{6} |

from 0 degree to 40 degrees, except for the case of the “Wing-body models” at Mach number 0.9 that have possibilities of excessive loads over the balance capability. The flow visualization of smoke-wire method was conducted in the low speed wind tunnel of Kyushu University to understand the flow field around the models.

Figures 3-5 show the results of aerodynamic coefficients at Mach number 0.3, 0.9 and 4.0. Here, the lift coefficient, drag coefficient and pitching moment coefficient are dimensionless number. These coefficients are defined by Equation (1) to Equation (3).

Lift coefficient

Drag coefficient

Pitching moment coefficient

Here, F_{z} is lift force, F_{x} is drag force, M_{y} is pitching moment, A is frontal projected area,

From

cross-sectional shape when the angle of attack is within 17.5 degrees, but those are obviously different as the angle of attack goes over 20 degrees. The “Square with wings” stalls obviously. On the other hand, the “Triangle with wings” does not show such the specific stalling as shown in the case of the “Square with wings”, and is obtained much larger lift coefficient compared with the “Square with wings” case. In addition, the difference of the lift coefficient between the “Triangle with wings” and the “Square with wings” in high angle of attack region is larger than the difference between the fuselage-alone models of “Triangle” and “Square”. This result indicates that the combination of the triangular cross-sectional fuselage and delta wings has a synergy aerodynamic effect which increases lift coefficient effectively.

From

The flow visualization was conducted by oil flow and smoke wire method to discuss the flow fields.

“Wing-body models” at angle of attack of 30 degrees, which showed a significant difference of the lift coefficient between the models.

For the “Triangle with wings” in

In

In

From these visualization results, the larger lift coefficient of the “Triangle with wings” compared with that of the “Square with wings” results from expanding the influence area of the separation vortex generated from the fuselage to the wing in the case

of “Triangle with wings”. In addition, the flow on the wing in the case of the “Square with wings” is separated.

In other word, it is presumed that the synergy effect of “Triangle with wings” which increases lift coefficient effectively referred to past studies [

An experimental study on examining aerodynamic characteristics of fuselage cross sections for RLVs was conducted at Mach number 0.3, 0.9 and 4.0 in the wind tunnel of ISAS, JAXA. This study revealed that the fuselage cross sections had large effects on aerodynamic characteristics in subsonic and transonic flow. The lift coefficient of the model having the triangular cross section with a set of fins was larger than that of the square model with a set of fins in high angles of attack region due to contributions of the separation vortices generated from the fuselage expanding to the wing surface. However, the qualitative tendency of the aerodynamic characteristics at Mach number 4.0 in supersonic region differed from the results in the subsonic and transonic region significantly. The aerodynamic characteristics at Mach number 4.0 were determined by the projected area only, which was caused by Mach number and Reynolds number effects.

Thanks to the following:

・ Open Journal of Fluid Dynamics for publishing this paper;

・ ISAS (Institute of Space and Astronautical Science) in JAXA (Japan Aerospace Exploration Agency) agreed with utilization of wind tunnel facilities;

・ Wataru Morita, graduated student at the time in Kyushu University, helped us to gather the aerodynamic data.

Tadakuma, K., Tani, Y. and Aso, S. (2016) Effect of Fuselage Cross Section on Aerodynamic Characteristics of Reusable Launch Vehicles. Open Journal of Fluid Dynamics, 6, 222- 233. http://dx.doi.org/10.4236/ojfd.2016.63017