Shape Control of Plates Using Piezoceramic Elements

the potential error magnitudes associated with angle bias. The effect of turbulence is also shown in comparing Figs. 2a and 2b. As would be expected, the increased turbulence tends to increase the PPD when the mean flow angle is close to parallel to the fringe planes. However, the PPD is slightly reduced when the mean flow angle is close to perpendicular to the fringe planes. Of particular interest are the results shown in Fig. 3, which were obtained using V f / V p = 2. As a rule of thumb, LV users typically use this ratio to ensure uniform instrument response for all flow angles, based on predictions of the Whiffen et al. theory. The data presented in Fig. 3 show that uniform instrument response is not achieved at V//VP = 2. For optical and flow parameters that are representative of those present in this experimental setup, the simulation shows that, for practical limits of Vf/Vp, perfectly uniform response will not be achieved. For example, using these parameter values and Vf/ Vp = 4, the simulation predicts a minimum PPD of 87% at a mean flow angle of 90 deg. Although this PPD is relatively high, it still does not ensure isotropic instrument response. Acknowledgments This work was performed under the auspices of Grant NGT-50868 provided through the NASA Langley Research Center while the first author was in residence at West Virginia University. The authors wish to thank James F. Meyers for suggesting the research presented in this paper.