Aerospace Science and Technology 104 (2020) 105879 Contents lists available at ScienceDirect Aerospace Science and Technology www.elsevier.com/locate/aescte Transient heat transfer measurements on pulsating and oscillating flows in a shock tunnel Gopalakrishna Narayana ∗ , Saravanan Selvaraj Department of Aerospace Engineering, Indian Institute of Science, Bangalore, India a r t i c l e i n f o a b s t r a c t Article history: Received 29 April 2019 Received in revised form 7 April 2020 Accepted 7 April 2020 Available online 9 June 2020 Communicated by Kostas Kontis Keywords: Shock tunnel Spiked-blunt body Unsteady heat transfer Pulsation Oscillation Flow visualization Flow field over high-speed vehicles can be changed drastically with the addition of a spike. These spiked bodies are associated with pulsation and oscillation unsteady flow phenomena on a spiked-body configuration. The flow separation leads to fluctuations in pressure and heat transfer of high amplitude and frequency. An investigation is made in this study, to measure the heat flux using platinum thin film sensors for these two unsteady flow characteristics, which would provide additional insights and may lead to better understanding of such type of flows. Experiments are carried out on a sharp-tipped spike attached to a flat face cylinder in a shock tunnel operating at Mach 5.7. Provisions are made to vary the spike length to diameter ratio (L/D), ranging from L/D = 0.75, 1, 1.25 and 1.5 for current investigation. The measured heat transfer varied from 100 W /cm 2 to 10 W /cm 2 for a pulsation case (L/D = 0.75) and whereas for the oscillation case (except for the corner gauges) the sensors indicate a heat transfer variation between 50 W /cm 2 to 5 W /cm 2 . In additions, the corner gauge shows a heat transfer of around 120 W /cm 2 to 10 W /cm 2 . This indicates the region of shock-shock interaction. The results from schlieren technique, used for visualization of the flow field is compliments the quantitative results.  2020 Elsevier Masson SAS. All rights reserved. 1. Introduction Re-entry research work is a vital goal for any advanced coun- tries in order to succeed in hypersonic transportation. Under- standing the hypersonic flow regime and the extensive knowledge about materials under re-entry conditions are essential, in order to achieve this goal. Development of reusable thermal protection system is one of the solutions for a successful hypersonic flight. Since, CFD fails to predict all necessary information under hyper- sonic flow conditions, there is a need for experimental research such as in shock tunnel. A re-entry flight/vehicle passes through several speed regimes, from highly hypersonic to low subsonic flow, which imposes severe heat load and aerodynamic drag on the vehicle. These vehicles are also characterised by the formation of curved bow shock in front of the main body, shock impinge- ment on the body and shock-shock interaction close to the body surface which in turn cause thermal loading. Heating levels rises to 30 times those encountered in an undisturbed stagnation flow. Attention is focused to reduce both the drag and heat load act- ing on the model by many researchers for vehicles as well blunt * Corresponding author. E-mail addresses: gopalakrishn@iisc.ac.in (G. Narayana), saravan@iisc.ac.in (S. Selvaraj). bodies with spikes. Aerodynamic devices such as aerospikes are used for rockets, missiles, and reentry vehicles. The wave drags and heat transfer rates on the nose surface of vehicles is reduced with aerospikes (due to separated flow) in supersonic and hyper- sonic flight conditions. Several applications of aerospikes such as M-3S-II rocket, the Japanese solid booster, has fixed aerospikes at the top of its two strap-on boosters to reduce atmospheric drag during its ascent and Tridents I and II are spike-nosed submarine- launched ballistic missiles. Separation flow around the aerospike configuration is essentially unstable. Robins (1953) [1] investigated the effect of several seeker-nose configurations. Many research areas targetted on the effects of spike and sepa- rated flows on aerodynamic characteristics of vehicle and they are proven to have lot of potential. Spiked body of hypersonic flows can appear in a variety of aerospace applications, such as ballistic missile drag reduction by spike [2–5], plasma or hot-gas injec- tion [6], and the ablation phenomenology associated with reentry problems [7,8]. By keeping different spike length and the flow con- ditions in the facility, both steady and unsteady flows appear over spiked-body geometries. Though, we have a thought in only one type of flow (unsteady) and however, it was found that two very distinct unsteady flow modes can exist such as pulsation and os- cillation. Experimentally investigated the driving mechanisms of instabilities [9] and however, there is a difficulty in obtaining an https://doi.org/10.1016/j.ast.2020.105879 1270-9638/ 2020 Elsevier Masson SAS. All rights reserved.