Extension of frequency modulated Doppler global velocimetry for the investigation of unsteady spray flows

• Frequency modulated Doppler global velocimetry is enhanced for field measurements.
• The progress is achieved by using either a scanner or a high-speed camera.
• When combined with particle imaging velocimetry, 2d3c measurements are obtained.
• Field measurement rates of ≥1kHz are demonstrated.
• As a result, velocity oscillations and transients are measured in an unsteady spray.

For the optimization of fuel injection, measurement techniques with a high temporal resolution below one millisecond are required to resolve the fuel spray velocity field in time. Since the measurement rate is usually too low to capture the temporal behavior of a single injection at once, a single measurement is performed during the injection and the injection is repeated with a variable time delay of the measurement. Consequently, non-stationary characteristics of the fuel spray cannot be resolved. For this purpose, a high measurement rate ≥1kHz is necessary in addition to the high temporal resolution. While time-resolved particle imaging velocimetry (PIV) is capable of achieving such high measurement rates, Doppler global velocimetry (DGV) is either too slow or is restricted to velocity profile (1d) measurements. However, DGV is considered to be a useful alternative or complement to PIV due to its high optical robustness.For this reason, the frequency modulated DGV is enhanced to provide field (2d) measurements with rates of ≥1kHz. This is achieved either by using a micro scanner or by applying a high-speed camera. Both setups provided time-resolved velocity field measurements in a spray test object without repetition of the spray cycle. During each single run, the same characteristic oscillations were identified and the decrease of the velocity at the ending of the spray injection was resolved. Hence, the technique is applicable for analyzing transient, non-stationary spray phenomena.