Instantaneous pressure and material acceleration measurements using a four-exposure PIV system
- 1.6k Downloads
This paper describes a non-intrusive technique for measuring the instantaneous spatial pressure distribution over a sample area in a flow field. A four-exposure PIV system is used for measuring the distribution of material acceleration by comparing the velocity of the same group of particles at different times and then integrating it to obtain the pressure distribution. Exposing both cameras to the same particle field at the same time and cross-correlating the images enables 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 in synthetic images. An omni-directional virtual boundary integration scheme is introduced to integrate the acceleration while minimizing the effect of the local random errors in acceleration. Further improvements are achieved by iterations to correct the pressure along the boundary. Typically 3–5 iterations are sufficient for reducing the incremental mean pressure change in each iteration to less than 0.1% of the dynamic pressure. 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 turbulent flow field and sample results are presented.
KeywordsParticle Image Velocimetry Pressure Distribution Shear Layer Interrogation Window Synthetic Image
This work is sponsored by the Office of Naval Research of the United States (Program Officer Dr. Ki-Han Kim). The authors would like to thank Yury Ronzhes for the mechanical design of the testing body and Stephen King for building the timing control device. Bo Tao’s participation at the initial stage of this project and Shridhar Gopalan and Jun Chen’s valuable assistance are also gratefully acknowledged.
- Brennen CE (1995) Cavitation and bubble dynamics. Oxford University Press, OxfordGoogle Scholar
- Chang K-A, Cowen EA, Liu PL-F (1999) A multi-pulsed PTV technique for acceleration measurement. In: International workshop on PIV’99—Santa Barbara, 3rd, Santa Barbara, CA, USA, 16–18 September 1999, pp 451–456Google Scholar
- Christensen KT, Adrian RJ (2002) Measurement of instantaneous Eulerian acceleration fields by particle-image velocimetry: method and accuracy. Exp Fluids 33:759–769Google Scholar
- Gurka R, Liberzon A, Hefetz D, Rubinstein D, Shavit U (1999) Computation of pressure distribution using PIV velocity data. In: International workshop on PIV’99—Santa Barbara, 3rd, Santa Barbara, CA, USA, 16–18 September 1999, pp 671–676Google Scholar
- Huang HT, Fiedler HE, Wang JJ (1993) Limitation and improvement of PIV, part II: particle image distortion, a novel technique. Exp Fluids 15:263–273Google Scholar
- Lin JC, Rockwell D (2001) Organized oscillations of initially turbulent flow past a cavity. AIAA J 39:1139–1151Google Scholar
- Liu X, Katz J (2003) Measurements of pressure distribution by integrating the material acceleration. In: Cav03-GS-14-001, Fifth international symposium on cavitation (CAV2003), Osaka, Japan, 1–4 November, 2003Google Scholar
- Liu X, Katz J (2004) Measurements of pressure distribution in a cavity flow by integrating the material acceleration. In: HT-FED2004-56373, 2004 ASME heat transfer/fluids engineering summer conference, Charlotte, NC, USA, 11–15 July, 2004Google Scholar
- Press WH, Teukolsky SA, Vetterling WT, Flannery BP (2002) Numerical recipes in C/C++. The Press Syndicate of the University of Cambridge, CambridgeGoogle Scholar
- Roth GI (1998) Developments in particle image velocimetry (PIV) and their application to the measurement of the flow structure and turbulence within a ship bow wave. PhD dissertation, Johns Hopkins UniversityGoogle Scholar
- Southwell WH (1980) Wave-front estimation from wave-front slope measurements. J Opt Soc Am 70:998–1006Google Scholar