Surface Roughness Effects Nosetip Ablation Characteristics

A model is presented for predicting the onset, growth rate, and geometric characteristics of surface roughness on re-entry vehicle nosetips. The roughness is characterized by scallop patterns, which are shown to be an advanced stage of ring waves or crosshatch patterns. The patterns act as time-variable surface roughness which augments the convective heating rates and alters nosetip ablation. The predicted geometry of the scallop patterns yields a roughness density parameter for evaluating the heating augmentation. The model has been incorporated into a nosetip recession and shape change computer program, and the results are shown to agree with experimental nosetip ablation data.