Abstract <p>The effect of varying disk diameters on drag reduction and the flow field for a hemispherical blunt body equipped with a hemispherical disk spike and moving at a hypersonic velocity is investigated. Axisymmetric simulations are performed to evaluate the effects of various disk diameters on the characteristics of flow around the body. The results indicate that increase in the disk diameter up to an optimal diameter of 18 mm leads to a reduction in both the drag force and the heat load. For the greater disk diameters, the drag force increases instead of decrease, demonstrating that the larger disk diameters become ineffective in further improving the aerodynamic performance. A density contour analysis reveals that, as the disk diameter increases, the strength of the reattachment shock weakens; however, beyond a certain threshold, the shock strength increases, correlating with the rise in drag. These findings suggest that there exists an optimal disk diameter for minimizing the drag and the heat load, while the larger diameters lead to negative aerodynamic effects.</p>