2010

Cavitating Pump Dynamics Test Facility for Vehicle System Stability Modeling

altThe facility consists of a magnetic bearing-supported pump flow loop with an inlet flow pulser, inlet flow conditioner, inlet bandwidth-enhanced electromagnetic flow (EMF) meter, test piece, discharge collector, exit flow conditioner, exit bandwidthenhanced EMF meter, exit flow pulser, flow conditioner, loop flow meter, and a throttle valve. The flow pulsers at the inlet and exit of the test piece provide the perturbations on top of the mean flow. The test rig loop is stiff and structurally robust to minimize structural vibration coupling with the flow pulsations. High-frequency pressure and flow measurements at the inlet and exit are the key measured parameters.

One particular concern is accurately measuring the small flow perturbations with the desired frequency response. Typical flow meters are low-frequency or averaging meters that cannot capture the frequencies of the pulsing flow in the loop. A bandwidth-enhanced EMF meter, developed for this application, allows accurate measurements of the pulsing flow. The meter is a regular EMF meter that is driven at a higher excitation frequency to cover the intended measurement bandwidth. In addition, special signal processing extracts the time-varying flow component from the signal to capture the flow rate changes with the pulsing.

A series of tests was conducted on the Space Shuttle Main Engine (SSME) low-pressure oxidizer turbopump (LPOTP) inducer to replicate what was done in the 1970s at Caltech, and confirm the results from this new test facility. The tests compared the hardware, test procedures, and data reduction techniques against the earlier successful results and show that CN has a validated dynamic transfer function test platform.

The test platform is now in operation and being used to ensure that the next generation of rocket launch systems is safe and reliable.

This article was written by Kerry Oliphant of Concepts NREC, White River Junction, VT. The work was completed under a NASA Marshall SBIR grant contract by Dr. Daniel O. Baun, Principal Investigator. For more information, visit http://info.hotims.com/28058-319.

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