Abstract—Heat source addition to the axisymmetric supersonic inlet may improve the performance parameters, which will increase the inlet efficiency. In this investigation the heat has been added to the flow field at some distance ahead of an axisymmetric inlet by adding an imaginary thermal source upstream of cowl lip. The effect of heat addition on the drag coefficient, mass flow rate and the overall efficiency of the inlet have been investigated. The results show that heat addition causes flow separation, hence to prevent this phenomena, roughness has been added on the spike surface. However, heat addition reduces the drag coefficient and the inlet mass flow rate considerably. Furthermore, the effects of position, size, and shape on the inlet performance were studied. It is found that the thermal source deflects the flow streamlines. By improper location of the thermal source, the optimum condition has been obtained. For the optimum condition, the drag coefficient is considerably reduced and the inlet mass flow rate and its efficiency have been increased slightly. The optimum shape of the heat source is obtained too. Keywords—Drag coefficient, heat source, performance parameters, supersonic inlet. I. INTRODUCTION OR the airplanes and missiles that incorporate air- breathing engines, an inlet is needed to provide required air by the engine from the free-stream conditions. Inlets are one of the most important parts of these vehicles since it has the greatest contribution in producing the thrust with minimum losses, Fig. 1, [1]. Operation of the combustion is ensured by the incoming air with sufficient mass flow rate, total pressure, and Mach number. Therefore inlets are designed so that air is brought into engine with small disturbances and acceptable condition for combustion with minimum drag and total pressure loss [2]. High speed flow is Manuscript received April 30, 2008. This work was supported by the Engineering Research Institute, Tehran, Iran. Mohammad Reza Soltani is with the Department of Aerospace Engineering, Sharif University of Technology, Tehran, Iran (e-mail: m.soltani@sharif.edu). Mohammad Farahani is with the Department of Aerospace Engineering, Sharif University of Technology and Engineering Research Institute, Tehran, Iran (e-mail: farahani@ae.sharif.edu). Javad Sepahi Younsi is with the Department of Aerospace Engineering, Sharif University of Technology, Tehran, Iran (e-mail: j_sepahi@ae.sharif.edu). always accompanied by the shock waves that reduce the overall efficiency considerably. Today large numbers of fighters have external compression inlets. These inlets have subcritical, critical and supercritical operating conditions, Fig. 2. The best performance occurs in the critical condition where the normal shock is tangent to the inlet lip. In this condition the oblique shock that forms at the spike nose passes at the inlet lip, thus preventing the spilled air and consequently additive drag vanishes. However, since the critical condition is almost always unstable due to the free stream disturbances and changes in the flight Mach number; most inlets operate in subcritical condition. Consequently the inlet goes through subcritical or supercritical operation and its parameters vary. To prevent these undesired phenomena most inlets are design for the subcritical operation, hence it is allowed that some air deflects to the outer cowl surface. As seen from Fig. 2, the subcritical operation has undesirable effects on the performance. Fig. 1 Example of thrust distribution over a supersonic engine installation at M∞=2.2, [1] Fig. 2 Inlet performance in subcritical, critical and supercritical operation, [2] Performance Improvement of a Supersonic External Compression Inlet by Heat Source Addition Mohammad Reza Soltani, Mohammad Farahani, and Javad Sepahi Younsi F World Academy of Science, Engineering and Technology International Journal of Aerospace and Mechanical Engineering Vol:2, No:4, 2008 447 International Scholarly and Scientific Research & Innovation 2(4) 2008 scholar.waset.org/1307-6892/2446 International Science Index, Aerospace and Mechanical Engineering Vol:2, No:4, 2008 waset.org/Publication/2446