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Nozzle Definition
A large number of parameters is required to fully define the nozzle including geometries and materials of each component. Each parameter must be specified in the config file although its value may be overwritten if it is specified as a design variable.
The inner wall is parameterized using a 3rd degree B-spline. It is specified by the WALL keyword and a vector of B-spline coefficient coordinates WALL_COEFS, ordered x-coordinate first, then r-coordinate. The WALL_COEFS_DV vector is the same size as WALL_COEFS and is used to specify which coefficient coordinates are design variables. See the design variable section for more details. For example:
WALL= (BSPLINE)
WALL_COEFS= (0.0000, 0.0000, 0.1500, 0.1700, 0.1900, 0.2124, 0.2269, 0.2734, 0.3218, 0.3218, 0.3230, 0.3343, 0.3474, 0.4392, 0.4828, 0.5673, 0.6700, 0.6700, 0.3255, 0.3255, 0.3255, 0.3255, 0.3255, 0.3238, 0.2981, 0.2817, 0.2787, 0.2787, 0.2787, 0.2797, 0.2807, 0.2936, 0.2978, 0.3049, 0.3048, 0.3048)
WALL_COEFS_DV= (0, 0, 0, 0, 0, 1, 2, 3, 4, 4, 5, 6, 7, 8, 9, 10, 11, 11, 0, 0, 0, 0, 0, 12, 13, 14, 15, 15, 15, 16, 17, 18, 19, 20, 21, 21)
In the above case, there are 18 coefficients. It is important that the first two and last two have the same x and r coordinates. In addition, there is a duplicated coordinate near the throat to ensure good behavior during optimization.
Wall layers are defined in order starting with LAYER1, then LAYER2 and so on, from innermost to outermost. Each layer definition follows this format:
LAYER1= (LAYER_NAME, LAYER_GEOMETRIC_PARAMETERIZATION, LAYER_MATERIAL_NAME)
For example, the inner thermal layer of the nozzle can be defined as:
% Inner thermal layer takes the heat load
LAYER1= (THERMAL_LAYER, PIECEWISE_LINEAR, CMC)
LAYER1_THICKNESS_LOCATIONS= (0, 0.3, 0.6, 1.0)
LAYER1_THICKNESS_VALUES= (0.03, 0.03, 0.03, 0.03)
LAYER1_DV= (0, 1, 2, 0, 3, 4, 5, 6)
where it is given the name THERMAL_LAYER, defined with a piecewise-linear geometry and associated with the CMC (ceramic matrix composite) material definition.
A piecewise-linear geometry must have the locations of its breaks and the value at those breaks defined. The keyword LAYERNAME_THICKNESS_LOCATIONS is used to define a vector of normalized break locations and the keyword LAYERNAME_THICKNESS_VALUES is used to define a vector of values at each break location, as seen above.
The LAYERNAME_DV keyword is used to specify which break locations and values are design variables. The first half of the entries in the LAYERNAME_DV vector correspond to the break locations and the second half correspond to the break values. See the design variable page for more information.
A constant thickness layer is defined using the CONSTANT layer geometric parameterization keyword. An addition keyword, LAYERNAME_THICKNESS is required to define the thickness of the layer, for example:
% Air gap between thermal and load layers
LAYER2= (AIR_GAP, CONSTANT, AIR)
LAYER2_THICKNESS = 0.005