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Pump inlet

Cast pump housing with integral crossover passages (Inconel 718)

Pump outlet

One-piece titanium rotor with inducer, two impellers, turbine, and bearing surfaces

Split hydrostatic bearing housings (Incoloy 909)

Radial in-flow turbine

Housing for filtered bearing supply

Pump inlet

Cast pump housing with integral crossover passages (Inconel 718)

Pump outlet

One-piece titanium rotor with inducer, two impellers, turbine, and bearing surfaces

Split hydrostatic bearing housings (Incoloy 909)

Radial in-flow turbine

Cast turbine housing with vaneless internal volute

Turbine discharge flange

Turbine gas inlet flange

FIGURE 10-2. Exploded view of an advanced high-speed, two-stage liquid hydrogen fuel pump driven by a radial flow turbine. (Copied with permission of Pratt & Whitney, a division of United Technologies; adapted from Ref. 10-2.)

Cast turbine housing with vaneless internal volute

Turbine discharge flange

Turbine gas inlet flange

FIGURE 10-2. Exploded view of an advanced high-speed, two-stage liquid hydrogen fuel pump driven by a radial flow turbine. (Copied with permission of Pratt & Whitney, a division of United Technologies; adapted from Ref. 10-2.)

blades, and radial as well as axial bearing surfaces. A small filtered flow of hydrogen lubricates the hydrostatic bearing surfaces. The cast pump housing has internal crossover passages between stages. The unique radial in-flow turbine (3.2 in. dia.) produces about 5900 hp at an efficiency of 78%. The hydrogen pump impellers are only 3.0 in. diameter and produce a pump discharge pressure of about 4500 psi at a fuel flow of 16 lbm/sec and an efficiency of 67%. A high pump inlet pressure of about 100 psi is needed to assure cavita-tion-free operation. The turbopump can operate at about 50% flow (at 36% discharge pressure and 58% of rated speed). The number of pieces to be assembled is greatly reduced, compared to a more conventional turbopump, thus enhancing its inherent reliability.

The geared turbopump in Fig. 10-3 has a higher turbine and pump efficiencies, because the speed of the two-stage turbine is higher than the pump shaft speeds and the turbine is smaller. The auxiliary power package (e.g., hydraulic pump) was used only in an early application. The precision ball bearings and

Oxygen Dump mam impeller

Inducer impeller

Fuel outlet

-stage turbine

Fuel pump impeller

FIGURE 10-3. Typical geared turbopump assembly used on the RS-27 engine (Delta I and II Launch Vehicles) with liquid oxygen and RP-1 propellants. (Courtesy of The Boeing Company, Rocketdyne Propulsion and Power.)

Auxiliary hydraulic pump

2-stage spur reduction gears

Inducer impeller

Fuel outlet

-stage turbine

FIGURE 10-3. Typical geared turbopump assembly used on the RS-27 engine (Delta I and II Launch Vehicles) with liquid oxygen and RP-1 propellants. (Courtesy of The Boeing Company, Rocketdyne Propulsion and Power.)

Oxygen Dump mam impeller inlet menifokl

Fuel pump impeller

Auxiliary hydraulic pump

2-stage spur reduction gears seals on the turbine shaft can be seen, but the pump bearings and seals are not visible in this figure.

Approach to Turbopump Preliminary Design

With all major rocket engine components the principal criteria (high performance or efficiency, minimum mass, high reliability, and low cost) have to be weighted and prioritized for each vehicle mission. For example, high efficiency and low mass usually mean low design margins, and thus lower reliability. A higher shaft speed will allow a lower mass turbopump, but it cavitates more readily and requires a higher tank pressure and heavier vehicle tanks (which often outweigh the mass savings in the turbopump) in order to have acceptable life and reliability.

The engine requirements give the initial basic design goals for the turbopump, namely propellant flow, the pump outlet or discharge pressure (which has to be equal to the chamber pressure plus the pressure drops in the piping, valves, cooling jacket, and injector), the desired best engine cycle (gas generator or staged combustion, as shown in Fig. 6-9), the start delay, and the need for restart or throttling, if any. Also, the propellant properties (density, vapor pressure, viscosity, or boiling point) must be known. Some of the design criteria are explained in Refs. 6-1 and 10-3, and basic texts on turbines and pumps are listed as Refs. 10-4 to 10-8.

There are several design variations or geometrical arrangements for transmitting turbine power to one or more propellant pumps; some are shown schematically in Fig. 10—4. If the engine has propellants of similar density (such as liquid oxygen and RP-1), the fuel and oxidizer pumps will have similar shaft speeds and can usually be placed on a common shaft driven by a single turbine (F-l, RS-27/Delta Fig. 10-3, Atlas, or Redstone engines). If there is a mismatch between the optimum pump speed and the optimum turbine speed (which is usually higher), it may save inert mass and turbine drive gas mass to interpose a gear reduction between their shafts. See Fig. 6-11. For the last two decades designers have preferred to use direct drive, which avoids the complication of a gear case but at a penalty in efficiency and the amount of turbine drive propellant gas required. See Figs. 6-12, 10-1, or 10-2.

If the densities are very different (e.g., liquid hydrogen and liquid oxygen), the pump head rise* (head = Ap/p) is much higher for the lower-density propellant, and the hydrogen pump usually has to have more than one impeller or one stage and will typically operate at a higher shaft speed; in this case separate

*Pump head means the difference between pump discharge and pump suction head. Its units are meters or feet. The head is the height of a column of liquid with equivalent pressure at its bottom. The conversion from pounds per square inch into feet of head is: (X) psi = 144(X)/density (lb/ftJ). To convert pascals (N/m2) of pressure into column height (m), divide by the density (kg/m3) and g0 (9.806 m/sec2).

Two pumps on same shaft with outboard turbine.

Shaft goes through fuel pump inlet.

Two pumps on same shaft with outboard turbine.

Shaft goes through fuel pump inlet.

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