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Handbook of Turbomachinery Second Edition Revised - Ventech!

Handbook of Turbomachinery Second Edition Revised - Ventech!

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ise <strong>of</strong> approximately 700 ft at its design point. Shaft speed at this point is<br />

approximately 5,800 rpm. Inducer mass flow rate at the design point is<br />

around 1,300 lb/sec. The inducer is driven by a six-stage full-admission<br />

hydraulic turbine. Each turbine stage is identical and utilizes a stage reaction<br />

<strong>of</strong> around 30% for good efficiency. The drive fluid for the turbine is LOX at<br />

high pressure that is obtained from elsewhere in the engine system. Pressure<br />

at the inlet <strong>of</strong> the turbine is approximately 3,500 psia with a turbine<br />

discharge pressure equal to the pump discharge pressure. This allows both<br />

pump and turbine fluids to be discharged to a common duct. Leakage <strong>of</strong><br />

turbine drive fluid into the lower-pressure pump inducer hub cavity is<br />

controlled by a labyrinth seal as shown in Fig. 28. The tapered inducer<br />

momentum thrust, plus the pressure forces over the inducer inlet, discharge,<br />

and rear hub cavity, total an axial thrust force <strong>of</strong> somewhat in excess <strong>of</strong><br />

29,000 lb at the design operating point. The direction <strong>of</strong> this force is to the<br />

left in the figure. It would be desirable to negate as much <strong>of</strong> this load as<br />

possible by tailoring the turbine thrust so as to be equal and opposite the<br />

inducer thrust at the design operating point. In this example, the diameter <strong>of</strong><br />

the rotor labyrinth seal is set such that this goal is achieved. As one can see<br />

from the figure, decreasing the seal diameter acts to increase the rotor face<br />

area exposed to the turbine inlet pressure. By careful adjustment <strong>of</strong> this face<br />

area, the total turbine thrust is set to the same 29,000 lb as the inducer<br />

thrust, but in the opposite direction. Having fulfilled our goal at the design<br />

point, attention shifts to the <strong>of</strong>f-design regime. It happens that this<br />

turbopump must run satisfactorily down to a pump flow rate <strong>of</strong><br />

approximately 50% <strong>of</strong> design. An analysis similar to that for the design<br />

point must be conducted for the 50% flow case to determine the rotor axial<br />

thrust. For this turbopump, it turns out that the turbine thrust declines more<br />

Figure 28 Direct-drive inducer turbopump with rolling element thrust bearing.<br />

Copyright © 2003 Marcel Dekker, Inc.

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