Research On Typical Multidisciplinary Coupling Problems In Super/Hypersonic Flow Field

Super/hypersonic vehicles are the current research hotspot in the field of aerospace industry.With the increasing design Mach number of aircraft and the widespread adoption of thin-walled structures and flexible materials for optimizing aircraft performance,the problem of fluid-thermal-structural coupling in the flow field inside and outside the aircraft has become increasingly prominent due to the severe aeroelasticity and aerodynamic heating phenomena.Among them,the inlet system serves as an important part of the over/under turbine-based combined cycle(TBCC)engine,and the deformation and vibration behavior of its main aerodynamic component-splitter plate may prominently influence the propulsion performance under the pressure difference of both sides;while the blunt nose of the aircraft and its optimized configuration-spiked blunt body,which serves as the component that directly faces the high-speed freestream flow,may affect the aerodynamic characteristics and structural safety of the aircraft with its ability to stabilize the external flow field and to withstand thermal loads.Hence,it is of great importance to conduct multidisciplinary analysis targeting at key components of the aircraft forebody for its design and control.This thesis mainly carries out the following work:Firstly,a multidisciplinary analysis strategy based on computational fluid dynamics/computational structural dynamics(CFD/CSD)methods is established,and the fluid solver Fluent is integrated with the structural/thermal solver Abaqus through a coupling-process-control and data-exchange software Mp CCI(Mesh-based parallel Code Coupling Interface).The prediction accuracy of the deformation/vibration of the splitter plate/flexible panel in the inlet system,the calculation accuracy of fluid-thermal interaction,the simulation accuracy of the supersonic internal/external flow field,the selection basis for the turbulence model,and the feasibility of not incorporating the jet nozzle into the fluid domain are validated through five classic experimental benchmarks.Secondly,for the two common internal/external over/under TBCC inlet system,the effect of the fluid-structure interaction of the splitter plate on the performance of the inlet system is explored.Studies have shown that the flow field in turbojet mode of the internal over/under inlet system is able to absorb the disturbance of the splitter plate by self-adjustment,whereas the inlet in ramjet mode falls into the unstart state since the shock train loses stability quickly after being disturbed by the combined effect of the high back pressure and the difference of flowpath structure.In contrast,the fluid-structure interaction phenomenon in the external over/under inlet system is more complicated and challenging.The increase in the intensity of the cowl shock caused by the deformation of the splitter plate reshapes the pressure distribution in the entrance of the inlet,which enables the turbojet flowpath to resist larger back pressure disturbances.When disturbance comes from the upstream angle of attack variations,the increased shock intensity makes it easier to cause separation when interacting with the boundary layer at the inlet shoulder,which instead leads to the happening of inlet unstart in advance.Under the constant back pressure/dynamic back pressure of the ramjet mode,a method to suppress the drastic flow field oscillation through the fluid-structure interaction behavior of the flexible panel is proposed as well.Thirdly,for the structural optimization method represented by the spiked blunt body configuration,the advantages and disadvantages of the drag reduction and thermal protection schemes are explored and summarized under the background of fluid-thermal interaction.Studies have shown that although the aerodome has excellent heat protection performance that can reduce the peak heat flux of the spike nose and the blunt body reattachment area by 70.0%and 54.7%,respectively,the single use of spike still cannot avoid the large temperature gradient along the surface under long-term aerodynamic heating.For this reason,a new type of aerodome-jet scheme based on the sonic cooling jet and the hemispherical aerodome is further proposed.By introducing the double-aerodome configuration,the cooling jet and their combinations,it provides more comprehensive thermal protection for the blunt body.In addition,under the limited spike length,the application of the aerodome-jet scheme is validated,and another new scheme that combines the opposing jet and the aerospike is proposed.Based on the second scheme,the feasibility of the telescopic aerospike are discussed.Finally,a research on the flow field oscillation encountered by a special kind of aircraft forebody-the spiked cylinder during the super/hypersonic flight is conducted.The effect of the hemispherical aerodome on the suppression of flow field oscillation is studied.Results have shown that the flow mode outside the cylinder with a spike length of L/D=1.0 can be transformed from pulsation to oscillation when the aerodome size increases to D_A/D=23.0%.The driving mechanism of flow pulsation can be explained by the alternative domination of the axial movement of the high-pressure gas along the spike and the radial movement of the high-pressure gas along the windward surface of the cylinder.The exploration of the three-dimensional effect of the flow field has shown that the difference between the two-dimensional axisymmetric assumption and the three-dimensional calculation is narrow as long as flow pulsation can be suppressed by aerodome.Based on above simulation,the direct-connected wind tunnel is used to conducting blowing experiments on the spiked cylinder.The periodic pulsation process of the flow field outside the cylinder with a pointed spike is captured at non-zero angle of attack,and the effectiveness of the aerodome in suppressing flow pulsation is validated.In summary,the research work that focuses on the aircraft forebody includes three aspects:the fluid–structure interaction exploration and fluid–thermal interaction analysis of key components,and the suppression study of flow pulsation/oscillation.It provides a reference for the design of aircraft aerodynamic layout and thermal protection scheme of super/hypersonic vehicles,and also has guiding significance for promoting the engineering application of the combined cycle engine and spiked blunt body.