SATPC0036077 Tab 04 4 SOW.pdf

Performance Enhancements in Loci-STREAM for Rocket Engine

Combustion Applications

1. Background

The Fluid Dynamics Branch at NASA/MSFC has a need for robust, high-performance CFD tools to model mixing of propellants in tanks as well as reacting flows inside a Liquid Rocket Engine (LRE) Thrust Chamber Assembly (TCA). Due to the extreme environment inside of a TCA, reacting flow testing of LRE hardware often provides limited insight into the dynamic fluid environment produced when propellants first mix and react. CFD tools capable of reacting flow modeling within TCAs and simulation of individual components such as injectors, manifolds and ducting for a variety of propellants at various states can provide valuable insight into LRE performance and design as a complement to hot fire testing. Robust CFD tools to model propellant mixing in tanks as well as combustion are required to support current and future NASA missions.

The Loci-STREAM CFD tool is NASA/MSFC’s primary CFD simulation tool for the applications mentioned above. Over the past several years, NASA/MSFC has engaged, through several separate contracts, to develop new capabilities within Loci-STREAM to respond to these needs. In these projects, the development work was successful in implementing the new capability and demonstrating its use on the targeted application. Further development work is often required to mature the new innovation into a commercially valuable tool for general applications.

2. Scope

NASA/MSFC has the need for conducting reacting flow simulations using Loci-STREAM for a number of applications. NASA has identified several areas that require innovations to improve the functionality of certain models to enable utilizing Loci-STREAM for applications that are important to both NASA and industry. Specifically, injector applications involving investigation of combustion instabilities is one of the areas where NASA has identified that it requires additional support. An item of immediate interest to NASA is the investigation of combustion instability in an oxygen-methane (OX-CH4) multi-element, shear-coaxial, high-pressure combustor, referred to as the transverse instability combustor (TIC) rig, which has been experimentally studied at Purdue University.

The work will include only items pertaining to existing capability in Loci-STREAM. Limited additional development directly targeted toward an existing capability will be performed as necessary. The overall scope of this effort is two-fold:

(a) The contractor shall perform testing, validation and further improvement of previously developed and implemented features in Loci-STREAM, to advance Loci-STREAM toward an innovative, robust tool with enhanced usability by NASA and potential commercial industry partners.

(b) The contractor shall provide support for NASA/MSFC personnel for conducting reacting flow simulations using Loci-STREAM for rocket engine injectors.

3. Tasks

Task 1: Testing and Validation of the Homogeneous Reactor Model

A new capability is being developed in Loci-STREAM to allow for the generation of flamelet tables based on homogeneous reactor combustor simulations. Flamelet tables produced by this tool are compatible with the Loci-STREAM compressible_ flamelet_tf module. The tool is composed of three components:

1) The first component is a stand-alone program written in the C++ programming language that can be used to generate homogeneous reactor “flamelets”. Salient features of this capability include the following:

• Species and reaction mechanism input species critical property data is specified via a Cantera-style reaction mechanism and critical-properties database files.

• A so-called “complete” mixture Peng-Robinson equation of state (PR-EOS) for mapping the entire thermodynamic space of the combusting mixture (including the supercritical and subcritical regions) is employed. In the subcritical region, this PR-EOS allows for the presence of two-phase states.

2) The second component of the tool is the currently existing Loci-STREAM Flamelet Table Tool, which reads and aggregates “flamelets” produced by the stand-alone reactor into a flamelet table. The following additions to this capability to support homogeneous reactor “flamelets” have been made:

• A new flamelet reader has been incorporated to read homogeneous reactor flamelets.

• Additions have been made to link to the “complete” mixture PR-EOS provided by the stand-alone capability described above.

• Homogeneous reactor flamelet tables are essentially the same as the previous tables produced using flamelets from FlameMaster; however, certain variables are not appropriate for homogeneous reactor flamelets that contain two-phase thermodynamic states. These include the tabulated transport property parameters for thermal conductivity and viscosity. Thus, a new output format has been inserted into the tool for homogeneous reactor flamelet tables that contain two-phase states.

3) The third component of the tool is the currently existing Loci-STREAM compressible flamelet_tf module. Two flamelet table types, one for premixed and counter-diffusion flamelet tables and another for homogeneous reactor flamelet tables.

The overall Homogeneous Reactor Model discussed above will be further investigated.

Specifically:

• The contractor shall rigorously test and validate the Homogeneous Reactor model (HRM) using suitable model problems involving both hypergolic and non-hypergolic propellants.

Hypergolic combustion involving MMH and NTO has been previously conducted with Loci- STREAM using the Flamelet Progress Variable (FPV) model. Hypergolic combustion cases will be tested using the HRM. Moreover, test cases using OX-H2 and OX-CH4 as propellants will also be used to examine the robustness of the HRM approach.

• The contractor shall do a performance comparison between the Flamelet Progress Variable (FPV) model (which employs diffusion flamelets) and the newly developed Homogeneous Reactor model. The contractor shall quantify and document the differences between the FPV and HRM approaches using heat release profiles, wall heat fluxes, etc.

Task 2: Investigation of the Extension of the Diffusion Flamelet Model in

Cantera to Subcritical Flows

Cantera was adopted as the platform for generation of flamelets – the implementation of the two-point flame control in Cantera has allowed for the generation of gaseous subcritical and supercritical flamelet tables. An area of interest has been subcritical flame modeling, which contains liquid and gas phases. The work that was done using the Homogeneous Reactor Model studied the feasibility of including a simple but consistent model for phase change. This model assumes that during phase change, all species have the same vapor/liquid phase split. Currently, the implementation of the Peng-Robinson equation of state in Cantera only allows for gas state queries. In this task, the contractor shall conduct work that will involve the creation of a class derived from the current Peng-Robinson implementation, which allows for the presence of two-phase solutions using the same simplifying assumption discussed earlier. This will allow for the one-dimensional flame solver to have boundary conditions that are liquid-like and that transition in the domain to gaseous as heat from a flame raises the temperature. This implementation will be tested using a subcritical OX-CH4 flame in the counterflow diffusion flame configuration to examine the density over the domain.

Task 3: Application Support to MSFC Personnel

Contractor shall provide support to NASA/MSFC personnel for conducting reacting flow simulations using Loci-STREAM for applications of interest to NASA. One such application involves investigation of combustion instabilities in rocket engines – of particular interest to NASA is oxygen-methane (OX-CH4) combustion in a multi-element, shear-coaxial, high-pressure combustor, referred as the transverse instability combustor (TIC) rig which has been experimentally studied at Purdue University. This experimental combustor exhibits self-sustained transverse instability due to the impact of the vortical structures on the chamber walls; These flow structures contain unburned fuel and oxidizer so that their impact at the wall produces a concentrated region of unsteady heat release, which in turn non-linearly couples with the transverse acoustic waves leading to the observed instability. NASA is interested in conducting high fidelity CFD simulations of this combustor using the flamelet modeling methodology implemented in Loci-STREAM to study the combustion instabilities in this device. Furthermore, the CFD results will be used to validate the low-order combustion stability analysis tool called the Stable Combustion of Rocket Engines (SCORE).

The contractor shall provide support to NASA/MSFC personnel in conducting these simulations including flamelet table generation using Cantera as well as troubleshooting issues that may arise during the course of the CFD simulations.

4. Deliverables

The following documentation, reporting and deliverables will be required:

a) Final report pertaining to items identified in Tasks 1 and 2.

b) Delivery of updated versions of the Loci-STREAM models and associated tools, as required.

c) An updated User’s Guide covering use of the new and/or altered features at the end of the period of performance.

5. Deliverable Products

Item

Due Date

Number of Copies

Format

Distribution

1. Final Report and final release version of Loci-

STREAM,

the User’s manual for Loci-

STREAM

and associated tools.

Completion of Effort

Electronic

ER and PS

6. Period of Performance

6 months