Drag Reduction Using Aerodisks for Hypersonic Hemispherical Bodies

The main challenge facing the designers of hypersonic vehicles is the significantly high levels of pressure drag and aerodynamic heating. Although blunt noses are preferred for better heat distribution, they introduce substantial drag to the vehicle. Spikes and aerodisks proved to be efficient drag and heating reduction devices. However, for some How conditions and model designs, the flow around spiked bodies can be unstable, which deteriorates their effectiveness. In the present study, a numerical investigation was conducted on a hemispherical body equipped with a spike of variable length and a hemispherical aerodisk of variable size in laminar hypersonic freestream conditions. A mechanism is proposed to explain the drag reduction and the cause of flow instability based on the shape of an effective body. In addition, the dependence of drag reduction on the spike's detailed design was investigated. For the models investigated in this work, an optimum aerodisk size produced the minimum drag and this optimum size was found to be inversely proportional to the spike length.