SpinOffs

The great engineer, Dr. Nikola Tesla, is best known for his work with alternating current (AC) electricity, but, did you know that he patented a bladeless type of turbomachinery in 1913? Called the Tesla Turbine, he developed it while trying to make an engine that was light enough to power his ultimate goal of building a “flying machine”. Tesla-type turbines can also be referred to as multiple-disk, friction, shear-force, or boundary layer turbomachinery.

The Refprop program

The calculations in the National Institute of Standards and Technology (NIST) Refprop program are generally considered the most accurate thermo-fluid models available.  The routines are widely used in many applications. 

The models

Several different models are embedded in the Refprop formulation. The most important are the  Benedict-Webb-Rubin equations of state for the pressure-temperature-density relationship. 

Space launch vehicles can exhibit self-excited longitudinal oscillations, also known as “Pogo” — so named because the phenomenon vibrates the rocket up and down in a manner similar to bouncing on a pogo stick. The vibrations severely impair the astronauts’ ability to pilot or respond to emergencies and can cause structural failure of the vehicle. NASA first became aware of the disastrous consequences from Pogo during the Gemini-Titan program. The issue continued to plague the agency through the Saturn V Moon launch missions.

High-efficiency, low-cavitation pumps often require a screw type inducer to treat the inflow to the main radial/mixed flow pump blades. Efficiency and head rise, split between inducer and main pump, are questions explored during the design process. Another important design consideration is the tolerance to cavitation. Finding the best solution, when there is often a trade-off between two or more operational conditions, is difficult. We have found that multi-objective optimization, for single or multiple operating points, is the best tool to use.

Cavitation occurs in a pump when the bulk liquid pressure starts to approach the vapor pressure of the liquid, and cavities of vapor form as seen in Figure 1.  This figure shows the inlet of a cavitating pump tested in Concepts NREC’s water flow loop.  These cavities can degrade the head rise and efficiency of the pump, create instabilities, and cause significant damage to the pump impeller and other components.  To avoid these effects, a pump must operate with an inlet head that is at least as high as the required net positive suction head (NSPH) that the pump was designed to achieve.  The NPSH is the difference in the inlet head and the liquid vapor head (or vapor pressure converted to liquid head).  Many pumping systems would benefit from the ability to operate at lower NPSH and so reducing the required NPSH of a pump is often of great concern to pump designers.