Aerospace Science and Technology 42 (2015) 196–208 Contents lists available at ScienceDirect Aerospace Science and Technology www.elsevier.com/locate/aescte Optimization and analysis of shock wave/boundary layer interaction for drag reduction by Shock Control Bump K. Mazaheri 1 , K.C. Kiani 2 , A. Nejati 3 , M. Zeinalpour 4 , R. Taheri 5 Center of Excellence in Aerospace Systems, Sharif Univ. of Technology, Tehran, Iran a r t i c l e i n f o a b s t r a c t Article history: Received 3 August 2014 Received in revised form 10 December 2014 Accepted 14 January 2015 Available online 22 January 2015 Keywords: Shock Control Bump Shock wave/boundary layer interaction Drag reduction Transonic flow Optimization Shock Control Bump (SCB) is a flow control method which reduces the wave drag through introducing a small bump over the wing surface. The present paper is mainly devoted to numerical investigation of shock wave/boundary layer interaction (SWBLI) as the main factor influencing the aerodynamic performance of transonic bumped airfoils. The survey is conducted for three airfoils through detailed SCB shape optimization processes employing differential evolution algorithm (DE). SWBLI is analyzed thoroughly for clean and bumped airfoils and it is shown how the modified wave structure originating from upstream of SCB reduces the wave drag while simultaneously improving the boundary layer velocity profiles downstream of the shock wave. The present work extends the conventional approach for SCB design via detailed interpretation of the decay of mean velocity defect downstream of the bumped airfoils. The numerical analysis of bumped airfoils in case of high transonic Mach number shows that taller SCB required for weakening the strong shock wave results in large separated flow zone and its performance improvement is deteriorated.  2015 Elsevier Masson SAS. All rights reserved. 1. Introduction Reducing aerodynamic drag in transonic regimes is one of the main challenges facing airplane design engineers. Simulta- neous presence of several physical phenomena affect flow com- plexity in these regimes, i.e. shock waves, flow instability, shock wave/boundary layer interaction (SWBLI), boundary layer thicken- ing, and boundary layer separation [1,2]. Due to these phenomena, there is a critical Mach number, beyond which the aerodynamic performance falls rapidly. However, adaptive wings can be em- ployed in order to postpone this abrupt behavior variation in tran- sonic flight. An elementary usage of this idea is done by Evans et al. [8]. They incorporated leading and trailing edge variable cam- ber mechanisms to improve maneuverability and performance in F-111. In 1992, Ashil et al. [4] introduced shock control bump (SCB) in NLF airfoils; a new concept in adaptive surface design which E-mail addresses: mazaheri@sharif.ir (K. Mazaheri), kiarash@ae.sharif.ir (K.C. Kiani), a_nejati@ae.sharif.ir (A. Nejati), m_zeinalpour@ae.sharif.ir (M. Zeinalpour), ramintaheri7@gmail.com (R. Taheri). 1 Professor of Aerospace Engineering. 2 Ph.D. Candidate. 3 Ph.D. Candidate. 4 Ph.D. Candidate. 5 Graduate Student. uses a confined region of the airfoil and has significant effect on the strength of incurring shock wave. It is shown that aerodynamic surfaces modified with SCB provide higher lift, lower drag, and delayed buffeting resulting in improved aerodynamic performance [12,13]. Although traditional methods of flow control such as suc- tion/blowing, vortex generators, and cavity ventilation have been studied extensively and have proved to be quite effective regard- ing aerodynamics performance in transonic regimes [17], detailed studies on SCB have shown more promising results especially com- pared to cavity ventilation, suction [17,14] and thermal methods [5]. The efficacy of SCB is quite sensitive to its shape and loca- tion, which of course strongly depends on airfoil geometry and free stream condition. Diverse studies are devoted to the design of the shape and location of the bump, e.g. [13,20,16]. These studies can be divided into two categories: (a) shape optimization, e.g. [13] and [14], and (b) parametric analysis, e.g. [20]. Recently the idea of SCB is extended to 3D wing applications [22,21]. Furthermore, SCB based hybrid flow control methods are also used to take advantage of both concepts. For instance, Yagiz et al. [23] have studied wave drag reduction based on bump and suction/injection in transonic regime. In this article we make three contributions in application of SCB to transonic airfoils. First, we introduce and apply two dif- ferent strategies for bump optimization: constant angle of attack http://dx.doi.org/10.1016/j.ast.2015.01.007 1270-9638/ 2015 Elsevier Masson SAS. All rights reserved.