Discussion: “The Lomakin Effect in Annular Gas Seals Under Choked Flow Conditions” (Arghir, M., Defaye, C., and Frêne, F., 2007, ASME J. Eng. Gas Turbines Power, 129, pp. 1028–1034)

The authors’ predictions that choked flow in an annular gas seal is likely to produce negative direct stiffness was recently borne out in tests conducted by the discussers. A smooth seal was tested in air with supply pressure $18.3bar$ and discharge near atmospheric pressure. The seal has dimensions: $L=100mm$⁠, $D=100mm$⁠, and radial clearance $Cr=0.305mm$⁠. The measured direct static stiffness is negative, $K=−1.93MN∕m$⁠. The model available to the discussers is based on the work of Kleynhans and Childs (1) and would not converge at the full pressure differential. The direct stiffness predicted by this model becomes negative and its magnitude increases as the input supply pressure increases from $∼10bars$⁠, but the code stops converging above a $δP$ of $∼...$