Project example: NMR Microturbine

Nuclear magnetic resonance (NMR) spectroscopy is a popular research technique used to determine physical and chemical substances and properties. Samples are spun in a strong, static magnetic field and exposed to high-frequency pulses.

Fig. 1: Contour plot of the flow rates around the microturbine — Contour plot of the flow rates around the microturbine

A gas-powered microturbine 1.3 mm or less in diameter generates this rotation. The high frequencies of up to 100 kHz, which are key in this process, cause lossy flow effects such as recirculation, separations and compression shock.

Fig. 2: Flow curve for a drive nozzle — Flow curve for a drive nozzle

Maximising the speed at a defined system pressure requires optimising the turbine geometry and the housing.

The goal of this project was to investigate the flow conditions at different operating speeds to derive approaches for increasing the efficiency of the turbine.

Findings

Fig. 3: Pressure distribution on the microturbine — Pressure distribution on the microturbine

The results of the simulation show excellent conformance with the measurement series.

The simulations showed that with this system configuration’s periodic pressure peaks will occur on the convex sides of the vanes, inducing a section modulus.

The findings further show that the seven drive nozzles negatively affect each other. This provided initial approaches for optimisation whilst adhering to the available production options.