Abstract: A non-intrusive technique for measuring the instantaneous spatial pressure distribution over a sample area in a flow field has been developed. This technique utilizes four-exposure PIV to measure the distribution of material acceleration, and integrates it to obtain the pressure distribution. Two cameras and perpendicularly polarized Nd:Yag lasers are used for recording four exposures on separate frames. Images 1 and 3 are used for measuring the first velocity distribution, whereas images 2 and 4 provide the second velocity map. The material acceleration is calculated from the velocity difference in sample areas shifted relative to each other according to the local velocity. Exposing both cameras to the same stationary particle field and cross-correlating the images enables the precision matching of the two fields of view. Application of local image deformation correction to velocity vectors measured by the two cameras reduces the error due to relative misalignment and image distortion to about 0.01 pixels. An efficient and accurate acceleration integration algorithm has also been developed. Validation tests of the principles of the technique using synthetic images of rotating and stagnation point flows show that the standard deviation of the measured pressure from the exact value is about 1.0%. This system is used to measure the instantaneous pressure and acceleration distributions of a 2D cavity flow field and sample results are presented. 1

In turbulence research, the velocity-pressure-gradient tensor in the Reynolds stress transport equation is critical for understanding and modeling of turbulence. Pressure is also of fundamental importance in understanding and modeling of cavitation. Motivated by the lack of experimental tools to measure the instantaneous pressure distribution away from boundaries, the paper introduces a non-intrusive method for simultaneously measuring the instantaneous velocity and pressure distribution over a sample area. The technique utilizes four exposure PIV to measure the distribution of material acceleration, and integrating it to obtain the pressure distribution. If necessary, e.g., for cavitation research, a reference pressure at a single point is also required. Two cameras and perpendicularly polarized Nd:Yag lasers are used