Drag Reduction

If aircraft flies faster than present velocity, it needs to fly faster than sonic speed.
The velocity which is faster than sound is called supersonic. The problem of the supersonic flight is its poor aerodynamic performance.
In order to solve this problem, it is proposed to heat air with laser. Our laboratory is researching on how to make more efficient supersonic flight by using this method.

Fig.1 Drag reduction method for SST(Super Sonic Transportation)

About reserach

The goal of this investigation is to realize a commercial supersonic transportation which has not been operated after the abortion of Concorde. One major reason that led to the abortion of Concorde was its poor performance of fuel efficiency. The large wave drag caused by shock waves is occurred during supersonic flight. This drag does not exist during subsonic flight. This drag increment leads to worsen the fuel efficiency.
The objective of this investigation is to improve the aerodynamics performance of supersonic transportation by using the interaction between low density bubbles generated by repetitive laser pulses and shock waves. This method is called “Fly by Light Power(FBLP)” and we are approaching our reserach from two perspectives: experimental and numerical investigations.

Current outcome

Fig.2 Experimental apparatus

The supersonic wind tunnel that we use for our experiment is designed by students in our laboratory(Fig.2). The test model is 20mm diameter cylinder. Bow shock made by Mach 1.94 flow and low density babble generated by laser irradiation interacts. This interaction makes bow shock moderate and creates vortex rings. This phenomena decreases the drag of the cylinder model about 20%, and the η(energy deposition efficiency) reached 10(Fig.3~5). From numerical simulation, it has been found that vortex rings generated by baroclinic effect have large effect on for drag reduction mechanism.

Fig.3 Bow shock deformation
Fig.4 Drag profile
Fig.5 energy deposition efficiency
vs.input energy
How to Drag Reduction?

Fig.6 Baroclinic effect


Fig.7 Virtual cone

Interaction between density gradient and pressure gradient generates vorticity. This phenomena is called ‘baroclinic effect’.(Fig.6). In our experiment, shock wave generates pressure gradient at the front and the behind of it, and laser heating generates low density babble. Baroclinic effect occurs when shock wave and low density babble interacts. Subsequently, vortex rings like doughnut is generated in front of the test model.
By increasing repetitive frequency of laser, more vortex rings stay in front of the test model . It creates the area which called ‘Virtual cone’(Fig.7). Virtual cone acts as cone attached in front of the cylinder test model. It makes bow shock attenuation. Consequently it reduces the drag.

blunt-cylinder body

0kHz laser energy deposition

80kHz laser energy deposition

other movies

Related Journal

  • T. Sakai, Y. Sekiya, K. Mori, and A. Sasoh, Proceedings of the Institution of Mechanical Engineers, Vol. 222, Part G: Journal of Aerospace Engineering, pp. 605-617, 2008.
  • Sakai,T,”Supersonic Drag Performance of Truncated Cones With Repetitive Energy Depositions “,The International Aerospace Innovation , Vol. 1, No. 1, pp. 31-43, 2009.
  • Jae-Hyung Kim, Akihiro Sasoh and Atsushi Matsuda, Shock Waves, Vol. 20, pp.339-345, 2010.
  • Jae-Hyung Kim, Atsushi Matsuda, Takeharu Sakai, Akihiro Sasoh, AIAA Journal, Vol. 49, No. 9, pp. 2706-2078, 2011.
  • Jae-Hyung Kim, Atsushi Matsuda, Akihiro Sasoh, Physics of Fluids, Vol. 23, ArtID 021703,2011.
  • Iwakawa A., Sakai T., Sasoh A., Transactions of the Japan Society for Aeronautical and Space Sciences, Aerospace Technology Japan, Vol. 11, pp.53-66, 2013.
  • Sasoh S., Kim J. H., Yamashita K., and Sakai T, Shock Waves Vol. 24, No. 1, pp. 59-67, 2014.
  • 岩川輝,大須賀健,摩嶋亮祐,酒井武治,佐宗章弘,  日本航空宇宙学会論文集,Vol. 62, pp. 99-106, 2014.

Sonic boom

Using an airplane for a long range can damage bodies of airplanes. In order to solve this problem, saving flight time is the most effective. However, most of modern airplanes flight at subsonic: slower than speed of sound. When airplanes fight supersonic: faster than speed of sound, people on the ground are force to hear detonating sound which is not observed at subsonic flight. Our team are doing research on how to reduce this noise to develop next generation supersonic transports. Besides, we undertake the joint study with JAXA(Japan Aerospace Exploration Agency).
Sonic Boom

Fig.1 Sonic Boom

When air planes flight at supersonic, shockwaves, expansion waves and other disturbances are induced. These are integrated in contagious process and the detonative sounds are observed on the ground. This phenomenon is called sonic boom. Because of the noise produced by sonic boom, supersonic flight is forbidden on the land. Therefore, reducing this noise is imperative to develop next generation supersonic transports.

Experiment with Ballistic Range

Fig.2 Ballistic Range

Our research develops the low boom aircraft by changing its shape. The study evaluates near filed pressure of super sonic free flight models not only by CFD but also by experiments which called ballistic range. The ballistic range can measure near field pressure without effecting stings. The availability of this equipment is limited in Japan. Thus, Our lab impliment research corporated with JAXA.JAXA APG.
Sonic Boom reduction with staged aft body

Fig.3 Sonic Boom reduction with staged aft body

From our research, it is indicated that attaching some steps to the model by changing its cross-sectional area in rear section has an effect on reducing sonic boom. Measuring near field pressure around supersonic free flight model by ballistic range is good for measuring flow around the model (especially flow of back of model) because a sting which is used in wind tunnel experiment is not needed.
Using this characteristic, we could demonstrate the reduction of rear sonic boom by experiments.

Related Journal

  • Akihiro Sasoh and Shin Oshiba, Review of Scientific Instruments, Vol. 77, No. 10, ArtID 105106, 2006.
  • Sasoh Akihiro, Takahiro Imaizumi, Atsushi Toyoda, Takeshi Ooyama,  AIAA Journal, Vol.53, No.9, pp. 2781-2784, 2015.

Shock Wave Boundary Layer Interaction


Shock wave and boundary layer Interaction (SWBLI) causes many serious problems to supersonic flight, such as unsteadiness of flow which leads to a decrease of engine performance, wing lift capacity and control surfaces effectiveness, as well as heat transfer and pressure loads which reduce the endurance of aircraft structures. To realize future supersonic transport, one of the important missions is to minimize negative impacts of SWBLI on supersonic vehicle.

Experimental approach

SWBLI was investigated by experimental approach. The hemisphere nose-cylinder-flare model configuration was used to study the interaction between the boundary layer of cylinder surface and the shock wave generated by flare part (Fig. 1). The adverse pressure from the flare-driven shock propagates upstream and leads to separated boundary layer as well as flow unsteadiness. Length of cylinder, angle and diameter of flare are changeable to achieve several of interaction states.


Fig. 1 SWBLI model configuration

Laser Energy Deposition (LED) method on flow control

In this study, we used LED as an active method to control the flow (Fig. 2). In detail, we took advantage of the low-density-bubble created by high repetitive laser pulses to suppress the separated boundary layer. By using LED, these bubbles interacted with the leading shock and transformed to vortex rings. In the next steps, the disturbance introduced by these rings induced the boundary layer transition so that it became “robust” against the adverse pressure gradient.  Osuka et al. (2014).


Fig. 2 Boundary layer modification by LED method

Flow control by LED

Using high repetitive laser with frequency up to 60 kHz, the LED method shows its effectiveness in separation control in case of weak interaction, corresponding to small-flare-angle model (Fig. 3). Besides, in case of strong interaction, the LED method shows the ability to reduce oscillation of flow (Fig. 4). Future studies will focus on the low-frequency unsteadiness which plays an important role to the structure fatigue by resonant pressure load.

swbli3w/o LED                                  f=60 kHz

Fig. 3 Separation control

 swbli5w/o LED                                  f=60 kHz

Fig. 4 Oscillation control

Related Journal

  • T. Osuka, E. Erdem, N. Hasegawa, R. Majima, T. Tmaba, S. Yokota, A. Sasoh, K. Kontis, Shock Waves, Vol. 26, No. 9, ArtID 096103, 2014.
  • T. Tamba, H. S. Pham, T. Shoda, A. Iwakawa, A. Sasoh, Physics of Fluid, Vol. 27, 091704, 2015.