Experimental Study on the Difference of Direct Damping Coefficients for Piston Ring End-Sealed Squeeze Film Damper With an Offset Groove

Abstract

Abstract The damping performance of squeeze film dampers (SFDs) is affected by feed hole distribution, feed pressure, and the number of feed holes. Common uncertainty differences exist between the direct force coefficients KXX and KYY, or CXX and CYY identified by the test. In this paper, the force coefficients identification test was carried out for a new piston ring end-sealed squeeze film damper with an offset groove. An original form of piston ring end seal, the double piston rings (DPRs), is tested and proven effective. The dimensionless direct damping coefficients CXX and CYY were identified using the instrument variable filter method (IVFM), and the absolute difference ΔC = abs (CXX – CYY) was calculated. Besides, the SFD damping performance was evaluated using the mean damping coefficient Cave = (CXX+CYY)/2. Last, the effects of feed hole distribution, feed pressure PH and the number of feed holes NH on the Cave and ΔC were investigated. The results show that the Cave and ΔC are affected by these factors. The Cave is larger (Cave > 3.0 at NH = 1), and ΔC is smaller (ΔC < 0.10 at NH = 1) when the feed holes are located upper than those located lower, and the more feed holes are located upper, the larger the Cave. In the low-pressure zone (PH < ∼1.5 bar), the Cave decreases as the feed pressure increases and increases as the feed pressure in the medium and high-pressure zones (PH > ∼1.5 bar). The Cave and ΔC can be slightly decreased by increasing the number of feed holes when the feed pressure is low, and yet the ΔC increases as the number of feed holes when the feed pressure is high. It is more effective to improve the damping coefficient by increasing the feed pressure than the number of feed holes, but the Cave will not increase significantly if the number of feed holes or feed pressure is increased continuously. The Cave and ΔC are related to the leakage and the evenly distributed form of internal oil, respectively. There may be a virtual threshold PNt that cannot be defined precisely for the feed pressure and the number of feed holes; the variation in feed pressure and the number of feed holes in the same direction results in a diametrically opposed pattern before and after this virtual threshold PNt, and the influence of the number of feed holes dominates the decrease of ΔC before the PNt. In contrast, the influence of the feed pressure dominates after the PNt. A sensitivity analysis reveals that the number of feed holes in the medium and high-pressure zones significantly influences the fluctuation of ΔC (ΔC fluctuates in the range of 0.17 to 1.45). Moreover, the factor of feed pressure at NH = 6 may lead to abnormal fluctuations of the ΔC.