Engineering topics

Flack, R. D.

Publications and source records attributed to Flack, R. D..

5 records

NASA NTRS1986

Laser velocimeter measurements in shrouded and unshrouded radial flow pump impellers

Shrouded and unshrouded versions of a four-vaned radial flow impeller with a design flow coefficient of 0.063 were tested in a volute pump using a two-component frequency-shifted laser velocimeter. Velocity profiles were measured at six flow rates and at four radial and six circumferential positions in the volute. The variations of the velocity from blade to blade and in the axial direction were measured and are presented. A passage vortex caused by tip leakage and relative casing wall velocity was found in the unshrouded impeller. The tip leakage did not accumulate in the suction wake region; the suction wake region was only 30 to 50 percent as large in the unshrouded impeller as compared to the shrouded impeller. The slip was 30 percent higher in the unshrouded impeller and the variation of slip with flow rate is presented. At no measured position in the impellers did the slip factor reach unity; the closest approach was 0.90. Reverse loadings of the vanes at outer radii were found for flow rates below the impeller/volute matching point for both impellers.

Hamkins, C. P.↗

NASA NTRS1986

Flow visualization of secondary flows in three curve ducts

Streak photography flow measurements are made for secondary flows in three 90-deg curved ducts of square cross section and different radii of curvature, at Dean numbers of 15,000-36,000 and radius ratios of 0.5, 2.3, and 3.0. Attention is given to secondary flow patterns for three cross sections in each bend: the inlet zero-deg plane, the midpoint 45-deg plane, and the outlet 90-deg plane. After a rapid transition region, the pressure-driven secondary flow patterns were characterized by flow moving toward the outer curved wall at the axial midplane and returning to the inner wall along the duct walls. The 0.5-radius ratio elbow was found to have the greatest influence on upstream inlet conditions.

Sanz, G. M.↗

NASA NTRS1983

Effects of volute geometry and impeller orbit on the hydraulic performance of a centrifugal pump

Overall performance data was taken for a Plexiglas water pump with a logarithmic spiral volute and rectangular cross sectioned flow channels. Parametric studies were made in which the center of the impeller was offset from the design center of the volute. The rig was also designed such that the impeller was allowed to synchronously orbit by a fixed amount about any center. The studies indicate that decreasing the tongue clearance decreases the head at low flowrates and increases the head at high flowrates. Also, decreasing the volute area in the first half of the volute and holding the tongue clearance the same, resulted in a decreased head for low flowrates but performance at high flowrates was not affected. Finally, the overall hydraulic performance was not affected by the impeller orbitting about the volute center.

Flack, R. D.↗

NASA NTRS1981

Experimental measurements of the Space Shuttle main engine fuel and oxygen turbopump vibration characteristics

The vibration characteristics of the SSME (Space Shuttle main engine) are dealt with. The Space Shuttle engine consists of a main rocket nozzle and attached to it are high pressure fuel and oxygen pumps. Various vibration problems have been encountered with both the hydrogen and oxygen pumps. The vibration spectrum of the hydrogen and oxygen pumps has been analyzed by various techniques using synchronous tracking filters and FFT analyzers. The experimental data has been correlated to theoretical predictions of resonance frequencies.

Gunter, E. J.↗

NASA NTRS1980

Instability thresholds for flexible rotors in hydrodynamic bearings

Two types of fixed pad hydrodynamic bearings (multilobe and pressure dam) were considered. Optimum and nonoptimum geometric configurations were tested. The optimum geometric configurations were determined by using a theoretical analysis and then the bearings were constructed for a flexible rotor test rig. It was found that optimizing bearings using this technique produces a 100% or greater increase in rotor stability. It is shown that this increase in rotor stability is carried out in the absence of certain types of instability mechanisms such as aerodynamic crosscoupling. However, the increase in rotor stability should greatly improve rotating machinery performance in the presence of such forces as well.

Allaire, P. E.↗