Abstract—In this work, startability of the Busemann intake family with weak/strong conical shock, as most efficient intakes, via overboard mass spillage method is theoretically analyzed. Masterix and Candifix codes are used to numerically simulate few models of this type of intake and verify the theoretical results. Portions of the intake corresponding to various flow capture angles are considered to have mass spillage in the starting process of this intake. This approach allows for overboard mass spillage via a V-shaped slot with the tip of V coinciding with the focal point of the Busemann flow. The theoretical results, achieved using two different theories, of self- started Busemann takes with weak/strong conical shock show that significant improve in intake startability using overboard spillage technique. The starting phenomena of Busemann intakes with weak conical shock and seven different capture angles are numerically simulated at freestream Mach number of 3 to find the minimum area ratios of self-started intakes. The numerical results confirm the theoretical ones achieved by authors. Keywords—Busemann intake, conical shock, overboard spillage, startability. I. INTRODUCTION HE scramjet air intake is essentially a converging duct decelerating and compressing airflow and supplying the compressed air to the engine’s combustor. In order to minimize the pressure loss and have the most efficient compression, intake of air-breathing engine should be able to capture all incoming air, and a supersonic flow gets established throughout the intake at the design free-stream Mach number (i.e. intake should be started). In unstarted supersonic air intake, the flow inside the intake is subsonic after passing through a bow shock in front of the intake, and less airflow is captured with lower efficiency and pressure recovery [1]-[5]; thus, it is not suitable for the engine's operation. By designing the intake with an appropriate area ratio (the ratio of the exit area to the entry area of the intake), it is possible to control the startability of the intake. In order to start the intake spontaneously, the isentropic intake's area ratio should be more than Kantrowitz limit which is defined by Kantrowitz and Donaldson [6] and Kantrowitz [7] to predict the flow starting or unstarting in converging ducts. The Kantrowitz limit is determined by assuming a normal N. Moradian was with McGill University, Montreal, Quebec H3A0C3, Canada. She is now working as self-dependent researcher (corresponding author, phone: 514-758-2660; e-mail: niloofar.moradian@mail.mcgill.ca). E. Timofeev, is associate professor in Department of Mechanical Engineering, McGill University, Montreal, Quebec H3A0C3, Canada.(e-mail: evgeny.timofeev@mcgill.ca). R. Tahir is with Etobicoke, Ontario, M9V 1X1, Canada. (e-mail: rabi.tahir@rogers.com). shock at the intake entrance so that all incoming mass flow is captured by the intake. Then, the isentropic area ratio for the flow Mach number downstream of the shock represents the Kantrowitz limit of the intake area ratio. The intake area ratio must be equal or greater than the above limiting value for spontaneous intake starting. In Kantrowitz theory of fully enclosed intake, it is assumed that the flow downstream of the shock is quasi-one-dimensional, quasi-steady, and isentropic. During last decades, designers try to use different methods to lower the Kantrowitz limit to self-start intakes much easier. Many methods such as overspeeding, variable geometry, mass spillage via wall perforations, etc. are used by them to reach this goal. Arguably the best method to improve the startability of an intake is overboard spillage technique. The overboard spillage technique relies for starting an intake on the overboard spillage of the incoming flow during the starting process by moving the cowl toward downstream. In an unstarted intake, the flow which cannot pass through the intake exit gets spilled from the cowl region. The spillage amount is decreased by moving the shock toward the cowl lip until the shock reaches the coal lip. Then, if the Kantrowitz limit is satisfied, the shock is swallowed and the intake becomes started. Using overboard spillage technique to start different types of planar intakes is studied by Veillard et al. [8] and Sun and Zhang [9] theoretically and Hohn and Gulhan [10] experimentally investigated the improvement of planar intakes' startability using this technique. The outcomes of all these studies along with the numerical and analytical results of previous studies done by [11], [12] on startability analysis of Prandtl-Meyer intakes using overboard spillage technique, confirm the benefits of using this method to increase the startability of intakes. This improvement gets clearer from the study Rosli et al. [13] which showed that for low Mach numbers, overboard spillage increases startability up to 40% (in terms of area ratio). Thus, this technique is used as one of the best techniques to improve the startability of different type of intakes such as Busemann intake. Busemann in 1929 [15] outlined the theoretical aspects of an axial, conically symmetric, supersonic flow called Busemann flow and, subsequently, Taylor and Maccoll [16] published the second order differential equation for this flow. Later on, Molder and Szpiro [14] presented the basics of Busemann intake design and highlighted some idiosyncrasies of Busemann flow as explained above. Molder [17] showed that a Busemann intake can reduce the Mach number from 8.33 to 2.8 with a total pressure recovery of 91%. The existence of Busemann flow in a Busemann intake was shown Theoretical Analysis of Self-Starting Busemann Intake Family N. Moradian, E. Timofeev, R. Tahir T World Academy of Science, Engineering and Technology International Journal of Mechanical and Mechatronics Engineering Vol:11, No:5, 2017 926 International Scholarly and Scientific Research & Innovation 11(5) 2017 scholar.waset.org/1307-6892/10006919 International Science Index, Mechanical and Mechatronics Engineering Vol:11, No:5, 2017 waset.org/Publication/10006919