Numerical Simulation On Aero-optical Effect By High-order Algorithm

With the progress of hypersonic/supersonic aircraft research,optical imaging technique has been an important direction in precision guidance field.When an imaging guidance vehicle experiences high-speed flight in atmosphere,severe distortion due to light propagation through the disturbed freestream around the optical dome would result in image aberration,jitter,intensity attenuation,and ultimately profound reduction of guidance precision,and such physical phenomenon is termed as aero-optical effect.To bridge the gap between theoretical study and engineering application,investigation on numerical aero-optics is conducted by the WCNS-E-5 high-order algorithm.Based on validation and verification procedure,flowfield simulation and aero-optical behavior,as well as aero-optical mitigation strategies,are issued concerning the flow models of mixing layer,boundary layer and supersonic turbulent boundary layer with tangential wall-injection film abstracted from the practical optical dome with tangential cooling film.In current thesis,recent advances of aero-optical effect have been reviewed in an interdisciplinary perspective of aerodynamics and optical engineering.The commonly-used evaluation parameters are introduced in the first place,followed by various theoretical,experimental and numerical methods summarized in sequence.Whereafter,the author puts an eye on the research progress from three aspects,namely the impact of aero-optical effects on image aberration,the methods for aero-optical suppression and the flow structure examination via novel aero-optical detection method.An additional discussion focuses on the difficulty in numerical verification and validation attempts for aero-optical problems.Future prospects based on the development stages of aero-optical effect are proposed in the end.The high-order numerical method and ray-tracing strategies are introduced,with ray-tracing performances of these strategies in steady shock-wave flowfield discussed in detail.Aero-optical simulation could be decoupled into flowfield calculation and ray-tracing post-processing without considering interaction between light and flow structures.For unsteady flowfield simulation,the spatial discretization in Navier-Stokes equations is dealt with the explicit fifth-order weighted compact nonlinear scheme(WCNS-E-5),and third-order Runge-Kutta or implicit dual-time-step method is employed for time integration.The parallel communication strategy of message passing interface(MPI)is used to enhance the efficiency of large grid amount for turbulent flow simulation.With regards to ray-tracing post-processing,the optical path definition,the first-order Euler and third-order Runge-Kutta methods are considered.The author simulates supersonic steady-state oblique shock wave flowfield with given inflow condition using two sets of uniform grid,and compares the calculated OPL and OPD with theoretical solutions.Current simulation implies that the optical path definition method is employed in following ray-tracing procedure due to better performance on OPL and OPD calculation,while the remaining two others show advantage in capturing light aberration.Aero-optical effect induced by mixing layer is investigated sequentially.The classical Ma_∞1.36/1.91 supersonic commingling flow is leveraged in following study,and vortex merging and aero-optical behaviors by inflow disturbance control are conducted by two dimensional simulation in the first place.In three-dimensional calculation,the widely-used measured mean-velocity and turbulent intensity profiles are induced for attesting flowfield validation,as well as grid independent analysis on aero-optical behavior performed for verification.The following sections touch on aero-optical mitigation schemes by inflow control,namely super-harmonic and sub-harmonic with varying phase shifts,and white-noise disturbance.Results show that the superposed disturbance with a given frequency would exert resonance effect somewhere possessing the same intrinsic unsteady value,possibly leading to more detrimental aero-optical effect around such position.Sub-harmonic disturbance without phase shift and the white-noise disturbance methods are promising for aero-optical suppression in whole computational domain,while the white noise is preferred in practical application.Lastly,wind-tunnel test on wavefront aberration induced by a Ma_∞0.8/0.1 subsonic case is employed for numerical comparison,and results imply that sufficiently specified experimental conditions are vital for validation procedure.The Ma_∞2.9 supersonic wall-bounded turbulent flow is numerically studied,as well as the flowfield evolution and aero-optical suppression behaviors by wall cooling and blowing and suction schemes.The impacts of computational domain size and grid spacing on flow evolution and wavefront aberration lay the groundwork,followed by the grid independent analysis with experimentally-measured aero-optical statistical relation employed for verification and validation.Regarding different wall temperature conditions,the rationality of ameliorating aero-optical effect by surface cooling is consolidated,and numerical data are mutually verified with the analytical solution deduced from Sutton model in supersonic velocity range.Exerting cooling strategy towards the turbulent section takes on the discernable aero-optical reduction efficiency among the schemes issued in our study.In aero-optical control by unsteady wall blowing and suction schemes applied to laminar section,a proper intensity modifying the whole region into laminar state is suggested,and a sufficiently high suction scheme could also mitigate turbulence-induced aero-optical effect.Moreover,steady blowing and suction strategies show profound prospect in improving imaging quality downstream as a result of reduced flowfield fluctuation.The last section issues physical behaviors of different inflow species under the same total pressure and total temperature,and the monatomic molecular gas Helium,which possesses low capability in light aberration,is suggested as the control injection evidenced by the comprehensive performance of aero-optical and aero-heating effect if under proper operating conditions when taking simultaneous account.The turbulent boundary layer with tangential wall-injection film,or naturally the combinational configuration of mixing layer and turbulent boundary flow,is investigated in the last chapter where both aero-optical effect and adiabatic wall temperature by several flow control strategies are concerned based on the grid independent analysis results.In parametric study by variable-controlling approach,injection Mach number,total temperature and total pressure are issued with time-averaged aero-optical response and wall temperature under adiabatic condition calculated.There exists a universal contradiction that mutual realization of both aero-optical suppression and thermal protection is a great challenge,so that optimization for injection operating condition is suggested.When taking the case with inflow white-noise disturbance as the baseline,wall steady suction control under proper intensity contributes to both aero-optical and adiabatic wall temperature reduction in whole computational domain.What’s more,when specifying disturbance of basic frequency at the inlet boundary as the baseline case,the inflow super-harmonic control scheme could realize aero-optical mitigation distinctively,while no method shows efficiency in wall thermal protection.Current thesis concentrates on the aero-optics in engineering application by means of high-order numerical simulation.Based on verification and validation attempts,the investigation procedure from acknowledgement to effective aero-optical suppression is performed concerning canonical mixing layer,wall-bounded turbulent flow and the combinational configuration in sequence,which has a range of implication towards hypersonic/supersonic target-seeking vehicle design.