Transition due to heat-shield cavities on a Mars entry vehicle

The influence of heat-shield cavities on the forebody of the proposed Mars Science Laboratory entry vehicle has been investigated experimentally and computationally. Wind-tunnel tests were conducted on the 70-deg sphere-cone forebody of the vehicle with various cavity sizes and locations to assess their effects on convective heating and boundary-layer transition. The heat-transfer coefficients and transition locations were measured using global phos-phor thermography. Laminar and turbulent Navier-Stokes computations were performed to compare with the experimental aeroheating data and to determine boundary-layer parameters for use in correlation of the experimental transition data. Comparisons of laminar heating data and computations were found to agree to within the experimental uncertainty, but turbulent computations underpredicted measured heating levels by up to 20%, possibly because the cavities were not included in the simple computational geometry employed. The cavity transition data were analyzed to determine a correlation for transition to turbulence at a cavity in terms of cavity geometric parameters and computed boundary-layer conditions. This correlation was used to show that the vehicle could experience early onset of turbulent How in flight as a result of the presence of cavities.