Analysis of Force Coefficients and Dynamic Pressures for Short-Length (L/D=0.2) Open-Ends Squeeze Film Dampers

Gas turbine engine manufacturers push for increasingly simpler squeeze film damper (SFD) designs that can still provide necessary damping to suppress rotor vibrations and offer stability to rotor-bearing systems. The work in this thesis addresses to industry needs by analyzing the experimental and predicted dynamic force performance of a very simply configured test SFD. The SFD incorporates three lubricant feedholes spaced 120° apart, a single short-length (L/D=0.2, L=2.54 cm) film land with no central feed groove, no end grooves for the provision sealing mechanisms (open-ends), and a nominal radial clearance c=0.267 mm (c/R=0.004). Analysis of the SFD performing whirl orbits with various amplitude (r) and departing from various static eccentricity (es) endeavors to reveal the dynamic performance of SFDs to events in gas turbine engine operation such as a blade loss, or a change in eccentricity. Circular (rX=rY) whirl orbits of the SFD with amplitude r/c=0.05 to 0.71, and departing from static eccentricity, es/c=0 to 0.86 lead to identification of the squeeze film force coefficients and measurements of the dynamic film pressures over the various dynamic operating conditions. Comparisons of experimentally identified force coefficients to those predicted by a finite element orbit-based model as well as those predicted by the classical short-length open-ends SFD theory strive to evaluate the accuracy of the state-of-the-art in SFD performance prediction. Comparisons of experimental results for the current SFD (termed damper 1) against that of two SFDs with similar configurations (dampers 2 and 3) examined in prior art, advance the simplicity of SFD design by highlighting the effects of a smaller radial clearance (in damper 2) and the effects of end grooves (in damper 3) on SFD dynamic force performance. Experimentally identified force coefficients for the current damper (#1) show moderate growth with orbit amplitude and strong nonlinear growth with static eccentricity, in particular at a largely off-centered position. Added mass coefficients for damper 1 increase with static eccentricity and, unexpectedly, with orbit amplitude. The experimentally identified SFD force coefficients for damper 1 exhibit excellent agreement with predicted force coefficients from the orbit-based model and the short-length open-ends model for whirl orbits departing from centered to slightly off-centered positions (e/c < 0.4) and with a small orbit amplitude (r/c < 0.4). The fluid film dynamic peak-to-peak (p-p) pressures exhibit a strong growth with orbit amplitude, and a moderate growth with static eccentricity. Inconsistent increases in p-p pressure with whirl frequency demonstrate the occurrence of air ingestion for motions with a large orbit amplitude or departing from a large static eccentricity. Comparisons of the current damper (damper 1) with damper 2 and 3 demonstrate that the damping and added mass force coefficients closely follow geometric ratios (L/c)^3 and (L^3/c), respectively, derived from the short-length open-ends SFD model. Damper 2, with ~half clearance (c2=0.122 mm), produces eight times more damping and 1.9 times more added mass than does damper 1. Damper 3 with similar clearance (c3=0.254 mm) and slightly longer film land length (Leff=2.97 cm), produces just 1.75 times more damping and 2.12 times more added mass than does damper 1