Aerothermal Modeling using AeroTPS®

Introduction

Analyzing high-speed vehicles (hypersonic or re-entry) is a complex process. Until recently, each steps of this process was performed separately by different analysts using different software, often at separate organizations or sites. This process typically includes the following steps:

• Calculating aerothermal loads. Any change to the vehicle altitude, attitude, and Mach number requires a new set of aeroheating loads to be calculated, sometimes including complex interactions with shock fronts. Methods range from engineering approaches to full CFD solutions. It is computationally intractable to solve all possible conditions with a full CFD method, so some means of reusing data or interpolating and extrapolation from finite sets of runs is often required.
• Simulating the thermal protection system (TPS) response, including charring and ablation. The TPS calculations are typically 1-D solutions at specified locations around the outer mold line (OML), the surface of the vehicle. Closure with the external boundary layer is usually required. Because of the expense and because of the traditional separation of tools and analysts,  these 1-D solutions have typically assumed a static thermal boundary condition on the inner surface: a “reservoir” wall.
• Calculating thermal response of the structure below the TPS. The temperatures of the TPS support is critical to ensure the structural materials do not fail, or that sensors or cryogenic tanks and lines are adequately shielded.  A 3-D analysis is typical, using the results of the TPS analysis as the boundary condition around the vehicle (using a heat flux through the reservoir wall as a fixed input).

When performed separately, these steps require extensive communication between the analysts and data exchange between software to ensure each step keeps pace with the other steps. With the advent of AeroTPS®, C&R Technologies is automating this process, and enabling integrated sizing to be performed and “what if” scenarios to be investigated. The key improvements include:

• Calculating aeroheating loads. Aeroheating loads can be calculated by engineering methods, or by running CFD calculations, or by a unique hybrid approach (inviscid farfield CFD solutions providing coefficients of pressure to fast-solving boundary-layer methods). The CFD calculations can either be a transient solution for a given trajectory, or a matrix of steady-state solutions for a range of Mach numbers and angles-of-attack.
• Interpolating the CFD-solution matrix. If a matrix of CFD solutions is created, it can be interpolated for the trajectory of interest, largely dissociating the production of CFD solutions from the selection or prediction of the trajectory. When multiple trajectories are being evaluated (including sensitivity analyses), this option significantly reduces the number of CFD solutions required by reusing the stored solutions.
• Calculating thermal protection system (TPS) response, including charring and ablation. The TPS calculations are typically 1D solutions at specified locations around the outer mold line (OML), the surface of the vehicle. These 1D solutions will usually have a static thermal boundary condition on the inner surface.
• Calculating thermal response of the structure below the TPS. The temperatures of the TPS support is critical to ensure the structural materials do not fail. A 3D analysis is typical, using the results of the TPS analysis as the boundary condition around the vehicle.

AeroTPS is feature in the Thermal Desktop suite that allows the integration of the simplified aerothermal solution, the application of a trajectory-specific CFD solution, or the interpolation of a CFD-solution matrix with the TPS solution and the 3D finite element and/or finite difference thermal solution.

AeroTPS Integrated Solution

The AeroTPS integrated solution includes the following products (each licensed separately by their respective developers). Each product adds its own set of capabilities to the integrated solution.

• zPOD, developed by Zona Technology, Inc.
  • Constructs matrix of CFD steady state solutions (Mach and angle-of-attack)
  • Quickly interpolates CFD matrix for given trajectory
• ATAC, developed by ITT Industries
  • Imports CFD results or calculates aeroheating loads using engineering calculations, or applies a hybrid method (inviscid CFD plus engineering boundary layer solution)
• Calculates simplified aeroheating load calculations
• Calculates 1D TPS response including charring and ablation
• Provides shapes change calculations
• Thermal Desktop with SINDA/FLUINT, developed by Cullimore and Ring Technologies
  • Provides the graphical interface to ATAC and zPOD
  • Creates geometry for ATAC
  • Creates thermal/fluid model
  • Links ATAC and SINDA models
  • Initiates and controls solution
  • Provides postprocessing visualization

Figure 1 - Added menus and toolbars in Thermal Desktop (click image for larger view)

The AeroTPS interface includes a graphical interface for ATAC. This interface allows creation of a new ATAC model or importing an existing ATAC model, and initiating a stand-alone or coupled ATAC solution.

If a new ATAC model is being created, the user has the option of several surfaces of revolution (cone, sphere, cylinder, or 4-point arbitrary curve) or a general patch for arbitrary geometry. In addition to geometry creation, the interface includes the following data managers:

• Material manager
  • Property files
  • Roughness algorithms
  • Blowing correction factors
• Surface thermo-chemistry manager
• Environment manager
• Flow transition regimes and algorithms manager

Figure 2 - Orbiter geometry created using spherical nose cone and general patches created using CAD geometry

Figure 3 - Apollo module generated with sphere, 4-point curve and cone. Left image shows calculation points. Right image shows pressure calculated by ATAC.

While Thermal Desktop can be used to create and launch a stand-alone ATAC run, the real power of AeroTPS is found in the option to run an integrated ATAC/SINDA simulation. During the integrated solution, ATAC and SINDA are run simultaneously: the assumptions regarding the reservoir wall are eliminated: temperatures and fluxes are exchanged at user-defined intervals in order to conserve energy across the interface. The user-defined interval is determined by two simple controls: a maximum time interval and a maximum energy exchange criteria. This co-solution allows accurate thermal modeling below the TPS, including all capabilities of SINDA/FLUINT (heat loads, heat pipes, radiation, coolant loops, electronics and sensors, cryogenic tanks, etc.).

When the AeroTPS interface is purchased and installed along with zPOD, ATAC, Thermal Desktop and SINDA/FLUINT, a fully integrated aerothermal solution may be performed. The AeroTPS interface may also be purchased and installed with ATAC only to serve as a graphical user interface for ATAC. AutoCAD Version 2004 and higher is required for the use of AeroTPS.

Figure 4 - Interpolation allows independent meshes and calculation points	Figure 5 - Comparison of typical TPS 1-D model to ATAC/SINDA integrated model

A beta version of AeroTPS is included with Thermal Desktop, Version 5.2. Users wishing to try the interface or test the integated solution are encouraged to contact C&R Technologies for more information (a licensed copy of ATAC is required for integrated solutions).

Customization and Consulting

C&R also provides consulting and custom software solutions to specifically meet your needs.