Measurement of density field in fluids using self-optimizable background oriented schlieren (BOS) technique with flexible dynamic range*

We developed self-pattern determinable background oriented schlieren (BOS) technique using projected pattern using a projector, which technique has a potential for adjusting the dynamic range for measuring various density fields, such as a turbulent flow and acoustic field. BOS can measure the density field only requiring a background pattern and a camera. With comparing two background images, i.e. one with targets and another without, displacement field related to the measurement target is calculated using displacement detection technique. Existing BOS measurement utilizes a fixed background pattern. Our new method optimizes the suitable background pattern generated by a projector, based on one distorted image in Fourier domain (k-space) in each experimental condition. Our proposed method was compared with previous BOS method and theoretical values. This novel technique could quantify the density field with flexible dynamic range which is optimized for the density field.