Experimental and theoretical data are presented for two interchangeable swirl brakes designed in connection with the Space Shuttle Main Engine (SSME) Alternate Turbopump Development (ATD) High-Pressure Fuel Turbopump (HPFTP) program. The experimental data includes rotordynamic data for a extensive variation of test variables. Comparison of the swirl brake performance revealed that a non-aerodynamic swirl brake design proved as efficient and at times better than an aerodynamic design. For this reason a theoretical investigation using Computational Fluid Dynamics (CFD) was recently carried out. This modeling focused on predicting the seal inlet swirl ratio which is the primary swirl brake performance parameter. The non-aerodynamic swirl brake showed superior performance for a variety of test variable conditions. Strong separation vortices within the swirl vanes are the main reason for this finding.

Experimental dynamic-stiffness-coefficient results are presented for a high-speed, lightly loaded, load-on-pad, flexible-pivot tilting-pad bearing. Results show that the real part of the direct dynamic-stiffness coefficients are quadratic functions of the excitation frequency. This frequency dependency is modeled well by an added-mass coefficient, and the resultant [ M ], [ K ], and [ C ] matrix model is frequency-independent versus a conventional [ K ] and [ C ] model that is frequency dependent. The dynamics introduced by the additional pad degrees of freedom (including pad inertia and web moment stiffness) and the effects of fluid inertia in the lubricant film account for part of this frequency dependency. Experimental results are compared to numerical predictions from models based on: (i) the Reynolds equation, and (ii) a Navier-Stokes (NS) equations bulk-flow model that retains the temporal and convective fluid inertia terms. The NS bulk-flow model results correlate better with experimental dynamic stiffness results, including added-mass terms. Both models underestimate the measured added-mass coefficients for the full excitation range; however, they do an adequate job for excitation frequencies up to synchronous frequency. The frequency dependency predicted by using a [ K ] and [ C ] model can be removed by adding a mass matrix to the reaction-force model with either a Reynolds equation or a bulk-flow NS model, with a very considerable speed up in calculation of damped eigenvalues for rotor-bearing systems.

Multistage centrifugal pumps and compressors are among the most widely used pieces of rotating machinery in industry. A typical application demands the arrangement of several impellers mounted on a shaft that spin within a stationary case. Annular seals are the most common sealing devices used in this type of machinery. The annular seal design affects both (i) machinery performance in terms of energy conversion efficiency, and (ii) stability due to the interaction within the rotor and the stator through the fluid flow within the seals. Extensive numerical research of several liquid annular seal experiments is in progress, focusing on the patterns that experimentally and numerically provide larger resistance to flow, hexagonal cells (honeycomb) and equilateral triangular cells (isogrid), both constant depths. In the present paper, the geometric characteristics that define the leakage resistance of roughened seals are explored. First, the results of a parametric analysis are discussed, which include previous 2-D predictions and new simulations of multiple rectangular grooved seal geometries. The analysis is limited to the original clearance in the experiments, 0.175 mm. The results indicate that roughened surface to total area ratio, and the depth-to-length ratio are the primary parameters defining the leakage characteristics of these surfaces. Secondly, the effect of the roughness orientation on the friction factor characteristics of these surfaces is addressed. Previous numerical tests have shown that solving the flow up to the laminar sub-layer better captures the behavior of the friction-factor-to-clearance proportionality. Resolving this layer is demanding. Recent numerical studies show promise in reducing computational efforts by employing a simplified empirical model with extended wall functions, indeed avoiding including each roughness in the numerical domain. These studies evaluated the flow behavior in round-hole seals, a perfectly symmetric pattern. Contrary to round holes, nonsymmetric patterns; knurls, honeycombs, or isogrids, consistently provide larger friction factor values. The numerical evaluation of the leakage characteristics in the last two patterns indicates a non-negligible sensitivity to the pattern orientation in one of them.