Theories And Experiments On Complex Flow Field Deflectometric Tomography

The visualization and measurement of complex flow are of major importance inaerodynamics. Compared with other methods applied to flow visualization andmeasurement, deflectometric tomography, a noncoherent method for studying phaseobjects, has many merits such as simple optical configuration, large dynamic range,having no special requirement to light source, and adaptation to tough environment. In thisthesis, a basically complete theoretical system for deflectometric tomography isconstructed, which is supposed to give its guidance in investigating beam deflectionperformances, designing testing configurations, projection extraction methods, andoptimum reconstruction algorithms. Two kinds of rotatable deflectometric systems aredesigned, which is able to capture projection data over an angular range of 180°. Based onthe research of fringe analysis techniques and wave-front retrieval techniques forprojection extraction, a further data processing method is supposed, in which thedeflectometric data are denoised by wavelet-based procedure after projection datareduction. Two kinds of new algorithms are developed to improve the reconstructionaccuracy and applicability of deflectometric tomography. First, a new iterative algorithm,deflection angle revision reconstruction technique, is derived from the basic deflectionformula and distinguished by a high degree of flexibility in reconstructing a distributionfrom limited view-angles projections. A smoothing scheme is supplied for the ill-posedreconstruction. The precision and convergence of the algorithm are analyzed through anumerical simulation. Second, Tikhonov regularization method is developed fordeflectometric tomography to reconstruct two-dimensional distribution. A modifiedregularization technique is applied to the linear projection equations and the conjugategradient method is used to compute the regularized solution for the least-square equations.In numerical simulation, the approach produces reliable reconstructions by computingunderdetermined equations and overdetermined equations respectively for asymmetricaldistribution. Besides, a curved ray algebraic inversion technique, associated geometricalray tracing algorithm, is suggested for the reconstruction of strongly refracting fields.Furthermore, the deflectometric tomography technique is employed to measure orreconstruct the temperature field of butane flame, asymmetric temperature distribution with double-peak-like structure, three-candle flame temperature field, density field inrocket exhausted jet, symmetric and asymmetric density fields in supersonic flow. Someother methods, such as direct thermocouple measurement and computing fluid dynamicalanalysis, verify the validity of the reconstruction results of deflectometric tomography, andprove the important value of the technology in measuring complex flow field.