Cavitation in Sudden Gap Expansion as a Model for Synovial Joint Cavitation
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The sound of cracking joints, more commonly knuckles, is thought to be due to the cavitation and subsequent bubble collapse in the synovial fluid of the joint. This fluid is shear-thinning and rheopectic, confined within a synovial membrane sac, and surrounded by complex curved surfaces comprised of cartilage on bone. A simplified model potentially capturing the dominant physics of this problem is cavitation between axisymmetric parallel disks in an infinite domain. Two analytical models are found for this problem: the Stefan-Reynolds equation and Kuzma’s derivation. Analytical solutions for flow and pressure distributions are found using these simplified models. The disks are suddenly accelerated from an initial separation of a sub-mm gap, and the pressure at the center decreases to values well below the Blake-threshold, leading to cavitation. The initial work reported in this paper utilized Newtonian fluid, namely water, and is focused on comparing the observed and expected cavitation dynamics.