Seals are considered one of the important flow elements of a turbomachinery device.Traditional labyrinth seals have proven their performance functionality by reducing leakagerates. Significant improvements on labyrinth seal functionality were obtained through alteringthe design geometry of labyrinth seals to prevent contamination across a seal and maintainingsmall leakage flowrates. This results in a windback seal that has only one tooth whichcontinuously winds around the shaft like a screw thread. These seals are used in gas compressorsto isolate the gas face seal from bearing oil. A purge gas is passed through the seal into thebearing housing. The helical design allows the seal to clear itself of any oil contamination.Windback seal performance is controlled through changing the seal geometry. A 2D graphicaldesign tool for calculating the total and cavity leakage flowrates for windback seals isintroduced.The effectiveness of the Fluent CFD (Computational Fluid Dynamics) commercial codeto accurately predict the leakage rate for windback seals was evaluated. The objective is todetermine if CFD simulations can be used along with a few experimental tests to study windbackseals of this design with air as the working fluid. Comparison of measurement and predictionsfor a windback seal using the ????-???? turbulence model with enhanced wall treatment functions showpredictions and measurements comparing very well with a maximum difference of 5% forleakage rate. Similarly, the leakage rate of the tested smooth seal compares favorably with twodimensional CFD predictions, with a difference of 2%-11% and 8%-15% using laminar and ????-????turbulent flow models, respectively. The variation of leakage with shaft speed and pressure ratioacross the seals is accurately predicted by the CFD simulations. Increasing the rotor speed to15000 rpm increases the measured leakage flowrate for the windback seal by 2% at highdifferential pressure and 4.5% at low differential pressure, and decreases it by 10 % for thesmooth seal. The effects of seal clearance, tooth pitch, cavity depth and the tooth number of starts onleakage flowrate, velocity and pressure distributions were studied numerically for threedifferential pressures and four rotor speeds.
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