Polynomial Response Surface Approximations for the Multidisciplinary Design Optimization of a High Speed Civil Transport

Surrogate functions have become an important tool in multidisciplinary design optimization to deal with noisy functions, high computational cost, and the practical difficulty of integrating legacy disciplinary computer codes. A combination of mathematical, statistical, and engineering techniques, well known in other contexts, have made polynomial surrogate functions viable for MDO. Despite the obvious limitations imposed by sparse high fidelity data in high dimensions and the locality of low order polynomial approximations, the success of the panoply of techniques based on polynomial response surface approximations for MDO shows that the implementation details are more important than the underlying approximation method (polynomial, spline, DACE, kernel regression, etc.). This paper surveys some of the ancillary techniques—statistics, global search, parallel computing, variable complexity modeling—that augment the construction and use of polynomial surrogates

Investigation of Transpiration Cooling Effectiveness for Air-Breathing Hypersonic Vehicles

The thermal management of air-breathing vehicles presents formidable challenges. The high dynamic pressure flight trajectories, the necessity of reducing the aerodynamic drag, the extended flight duration time and the need for a reusable Thermal Protection System (TPS) are stringent requirements. The work presented in this paper is focused on transpiration cooling and investigates the effects of fluid injection into the hypersonic laminar boundary layers. In particular, a simulation model, which is composed of a coupled solution of Self-Similar Method (SSM) and a Difference-Differential Method (DDM), is introduced to study the transpiration cooling along a flat plate. The reduced order code is intended to assess the boundary layer characteristics and will serve as a research tool for the design and analysis of future experimental investigations in the UTA\u27s 2MW arc-heated facility that has been modified and is currently in use for TPS studies. The DDM solves a system of coupled algebraic and Partial Differential Equations (PDE) for the case of Pr=1 and Le=1. Self-Similar solutions are considered in order to compare the code results for the case without transpiration

Variable Transpiration Cooling for the Thermal Management of Reusable Hypersonic Vehicles

The overall aerodynamic performance of every flying vehicle is strongly dependent on near-wall effects. In the hypersonic regime, the viscous dissipation of the high-enthalpy flow over the vehicle is responsible for the generation of surface temperatures and heat fluxes that can easily exceed the thermo-mechanical limits of current materials. Based on these considerations, it is important to understand the physics that characterize the boundary layer and its interaction with the vehicleʼs surface in order to simulate its behavior for different surface parameters such as the type of material, surface manufacturing, surface coating, wall geometry, mass exchanges, etc. The work presented in this paper is focused on the mass exchanges at the surface, and investigates the cooling effectiveness of the proposed variable transpiration cooling concept for the case of hypersonic laminar boundary layers on a flat plate. A reduced order model that captures the relevant physics has been developed and implemented in a code that solves the Navier-Stokes equations written for stationary, non-reacting, hypersonic laminar boundary layers and neglecting the radiative thermal exchange. The code uses a coupled solution of Self-Similar Method and Difference Differential Method assuming a unitary Prandtl and Lewis number. Selected distributions of the coolant (air) transversal velocity at the wall have been considered to simulate the variable transpiration. The analysis reveals that the constant-linear wall velocity distribution minimizes the wall heat flux (for a specified wall temperature) along the flat plate if the total coolant mass-flow rate is kept constant. In addition, the saw-tooth wall velocity distribution allows for a reduction of nearly 37% of the required coolant mass with respect to the other cases. These results highlight the potential thermal-management implications of this concept applied to hypersonic vehicles. The comparison between the computationally inexpensive reduced order code (AERO-Code) and the high-fidelity Computational Fluid Dynamics code GASP shows similar qualitative and quantitative results on the heat fluxes and shear stresses prediction

Integrated Analysis for the Design of Tps based on Variable Transpiration Cooling for Hypersonic Cruise Vehicles

The thermal management of hypersonic air-breathing vehicles presents formidable challenges. Reusable thermal protection systems (TPS) are one of the key technologies that have to be improved in order to usehypersonic vehicles as practical, long-range transportation systems. Both the aerodynamic and the material performances are strongly related to the near-wall effects. The viscous dissipation within the hypersonic boundary layer, coupled with the high dynamic pressure flight trajectories, generates surface temperaturesfor which the strength and the environmental durabilityof the material can be widely exceeded.In this type of environment,active cooling systems have to be considered in order to afford long duration flights inhypersonicregime. Transpiration cooling represents apromising technique in terms of temperature reduction and coolant mass saving.In order to explore the potentialof this technique, it is important to understand the physics that characterize the boundarylayerand its interaction with the vehicle-s surface. The integrated analysis of the hypersonic boundary layer coupled with the thermal response of a porous mediumis performed here for aflat plate and a2-D blunt bodyconfiguration. A constant value of thetransversal wall velocity is used to simulate uniformtranspiration. A saw-tooth wall velocity distribution is used to simulatethe variable transpirationstrategy. An equalamount of coolantusage has been imposed in order to compare the cooling effectivenessin the two cases. The uniformtranspiration allows areduction of 49% onthe stagnation point heat flux in comparison with the case without transpiration. The variable transpiration reducesthe stagnation point heat fluxbyan additional7% with respect to the uniformtranspirationcase. The heat fluxes derivedfrom the solution of the hypersonic boundary layeras well as the imposed wall temperature are used to perform an integrated analysisthat includes the porous material.Thetest cases analyzed emphasize the importance of evaluatingthe influence of the material-s thermo-physical properties at the initial design stage.For the flight conditions consideredin this analysis a combination of low materialporosity and high thermal conductivity are necessary to generate the requiredinjection strategy. The integrated analysis is essential for the purpose of establishing the optimum transpiration strategy needed to maintain the surface temperatures in the required range. The change in the transpiration distribution along the vehicle surfaces (variable transpiration) allows to selectively cool down the structure in the regions where the higher heat fluxes are located (i.e. nose, leading edges)and diminishes the amount of requiredcoolant fluid.The transpiration for the blunt body can be limited tothe regionswhere thelocalwall heat flux is greater than or equal toapproximately20% of the stagnation point heat flux. This strategy allows the reduction of the total amount of coolant by 62% for the uniformtranspiration and by 58% for the variable transpiratio

Variable Transpiration Cooling: A New Solution for the Thermal Management of Hypersonic Vehicles

The overall aerodynamic performance of every flying vehicle is strongly dependent on near-wall effects. In hypersonic flows, the viscous effects near the wall have an even greater importance from the standpoint of thermal loads (i.e., heat flux and temperature distributions) and aerodynamic performance (i.e. L/D). Based on these considerations, it is important to understand the physics that characterize the boundary layer and its interaction with the vehicle\u27s surface to simulate its behavior for different surface parameters such as the type of material, surface manufacturing, surface coating, wall geometry, mass exchanges, etc. The work presented in this paper is focused on the mass exchanges at the surface, and investigates the cooling effectiveness of variable fluid injection into the hypersonic laminar boundary layer on a flat plate. A reduced order model that captures the relevant physics has been developed and implemented in a code that solves the Navier-Stokes equations written for stationary, no-reacting hypersonic boundary layer neglecting the radiative thermal exchange. The code uses a coupled solution of Self-Similar Method (SSM) and Difference-Differential Method (DDM) for a flat plate in the case of Pr=1 and Le=1. The variable transpiration is obtained choosing selected distributions for the coolant (air) velocity at the wall. The analysis of the minimization of the wall heat flux and of the coolant-s mass flow rate is performed. The comparison between the computationally inexpensive reduced order code and the CFD code GASP shows similar qualitative and quantitative results on the heat fluxes and shear stresses prediction

Integrated Analysis of Reusable Thermal Protection Systems Based on Variable-Transpiration Cooling

Reusable thermal protection systems are one of the key technologies that have to be improved to use hypersonic vehicles as practical, long-range, transportation systems. The proposed concept of variable-transpiration cooling is investigated in this work by coupling the hypersonic boundary-layer solution with the thermal response of a porous material. The simulations of the hypersonic boundary layers are obtained using an in-house-developed reduced-order model capable of handling generic injection velocity profiles at the porous wall and the high-fidelity computational-fluid-dynamics code Langley Aerothermodynamic Upwind Relaxation Algorithm. The material thermal response is included adopting a one-dimensional model for the porous medium. The integrated analysis is performed for a flat plate and a two-dimensional blunt-body configuration. A sawtooth wall velocity profile was chosen to represent the variable-transpiration strategy. The uniform transpiration on the blunt body allows for a reduction of the stagnation point heat flux by 48% in comparison with the case without transpiration. The variable transpiration reduces the stagnation point heat flux by an additional 8%. The integrated analysis highlights the coolant blockage effects, the potential offered by the variable-transpiration cooling, and the necessity of performing a coupled flow-material analysis, at the design stage, to define realizable combinations of porosity, thermal conductivity, and material thickness capable to guarantee the thermostructural integrity of the thermal protection system