Oxidizer Pressure Drop Analysis of Porous Hybrid Motor Grains

摘要

This work is a continuation of prior efforts focused on using structural data of porous hybrid motor grains acquired from x-ray computed tomography (XCT) to better understand the pressure drop of oxidizer in the grain during operation. Pressure drops from a set of previous motor firing tests1 are compared to theoretical predictions of existing empirical correlations.2 Predictions of pressure drop made based on bulk porosity measured with XCT and Archimedes methods disagree with experimental measurements of pressure drop. Motor regression plays a minor role in this disagreement. However, the functionally graded porous structure of the hybrid grains appears to exert greater influence. Previously, XCT data for porous hybrid motor grains was acquired and validated3.4 This data reveals that porosity towards the central region of the grains is significantly higher than the peripheral regions. This gradient in porosity suggests that the central region of the grain may play a more dominant role in the oxidizer transport, and overall porosity of the grain is not the best representation of the grain porosity within the correlations. As the Reynolds number increases, the effects of functionally graded porosity are suspected to be more pronounced. A plan to acquire more experimental data in order to test this hypothesis is conducted and detailed. Initial results are presented for tests in which the Reynolds number is varied from 1,800-16,000. These tests were performed within an apparatus that holds the porous hybrid motor grain. Reynolds numbers are controlled primarily through the adjustment of upstream pressure in a flow tube containing a fixed venturi choke point. Pressure is measured at the fore and aft ends of the grain. The measured pressure drop will be used in the establishment and validation of a new model for the pressure drop in porous media.