Modeling Techniques For Evaluating The Effectiveness Of Particle Damping In Turbomachinery

High power turbopumps are frequently used to supply propellants to the combustion chambers of rocket engines. Due to the high pressures and flowrates required, turbopump components are subjected to harsh environments which include dynamic excitation due to random, sine, and acoustic vibration. Additionally, fluid-induced forces can couple with the dynamics of the structure resulting in flow induced instabilities (flutter). Structural response to these forms of excitation results in reduced fatigue life and increases the likelihood of an operational failure. Particle damping has been used successfully on vibration problems in the past by increasing the damping and therefore reducing the response to acceptable levels. Empirical methods have typically been employed to evaluate the performance of the particles in reducing the structural response. This work explores the use of finite element methods to estimate the effectiveness of particle damping in a typical non-rotating turbopump component. Axisymmetric harmonic models are used to estimate the increase in modal damping produced by the addition of particles in the cavity of an axisymmetric seal. Target modes of vibration are evaluated to quantify how particle damping contributes to the total modal damping and how the total modal damping is altered by geometry changes in the seal design. Nomenclature UBs B = strain energy in seal material UBp B = strain energy in particle material UBT B = total strain energy ζBs B = damping ratio of the seal material ζBp B = damping ratio of the particle material ζBT B = total damping ratio α = scaling constant KE Bp B = kinetic energy of particle material KE Bs B = kinetic energy of seal material KE BT B = total kinetic energ