Data Analysis

Introduction

In the present study, particle image velocimetry (PIV) and hotwire anemometry (HWA) have been used for velocity field measurements in the spatial and temporal domains respectively. These measurements have been used to calculate the mean and statistical quantities describing the flow, i.e. mean and rms velocities, power spectra, vorticity, drag coeffcient, Strouhal number and turbulent kinetic energy. The details of calibration and data analysis procedures for these quantities are discussed below. The proper implementation of the measurement techniques is validated by comparing the recorded data against each other. The uncertainty in measurements is reported from a repeatability study. The measurements, experimental procedure and data analysis are validated from a comparison of Strouhal number and drag coeffcient data with the published literature a comparison of Strouhal number and drag coefficient data with the published literature.

Principle of Operation of PIV

Particle image velocimetry is a non intrusive technique for measuring the spatial distribution of the velocity within a single plane inside the flow The measurement is indirect, via the displacement of moving particle groups within a certain time interval. For this purpose the flow is seeded homogeneously with appropriate tracer particles. The concentration of the particles must be well adjusted with regard to the nest flow structures. It is assumed that the particles are small enough to move with the local flow velocity. A plane within the flow is illuminated twice within a short time interval by a laser sheet.