Abstract: Experimental study on the performance characteristics line of the turbine flow sensor is made, with a high precision experimental facility, which can regulate the viscosity and the flow of the diesel oil, and another one for the flow of the water. It is found that a zigzag appears at the performance characteristics line of the different sample of turbine flow sen-sor at low flow rate, even changing the characteristics of the fluid that is measured. The rang of the zigzag variation is great than ±0.5%. But the value of Reynolds number, where the second peak appears, varies when the characteristics of the liquid and the sample of the turbine flow sensor are changed. The analysis of this phenomenon and the stress of the rotor are shown. The boundary layer flow is formed when the fluid passes the turbine flow sensor. The transition of the modes of flow in the boundary layer leads a sudden increase of the driv-ing torque of the rotor. Maybe, this is the reason for the zigzag variation of the line.

Key words: Boundary layer, Modes of flow, Performance characteristics line, Transition, Turbine flow sensor, Lubricant, Minimum quantity lubrication, Oil mist characteristic, Penetration characteristic