CHARACTERIZING THE LEAKAGE FLOW OF BRAIDED FIBER SEALS

A new kind of high temperature flexible braided fiber seal has been de veloped for advanced hypersonic engine applications. Leakage flow expe rimental observations show that both engine pressure and preload press ure influence leakage flow rate. Although the Reynolds number is relat ively small (Re < 10), the mass flow rate comparison of air versus hel ium reveals that the leakage flow is not viscous dominant. The Ergun e quation describing flow through porous media is applied to the flow an alysis. The two constants in the Ergun equation, designated as the vis cous flow constant C(L) and the inertial flow constant C(T), are deter mined experimentally. For the leakage flow test setup and the seal geo metry, test data show that the values of C(L) and C(T) vary for differ ent seal fiber architectures. The relative magnitude of the non-viscou s flow effect can be determined using a dimensionless variable (ReC(T) /C(L)). If this variable is much less than 1, the nonviscous flow effe ct can be neglected. For the seals tested, the ratio of C(T)/C(L) is a t the range of about 1 to 2 in most cases. Therefore the criterion for the viscous dominant flow is Re < 0.1. Predictions of seal leakage fl ow using the Ergun equation show good agreement with experimental data of both fluid media, air and helium.