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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 will 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 by number 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 LAYER#_THICKNESS_LOCATIONS is used to define a vector of normalized break locations (normalized by nozzle length) and the keyword LAYER#_THICKNESS_VALUES is used to define a vector of values at each break location, as seen above.
The LAYER#_DV keyword is used to specify which break locations and values are design variables. The first half of the entries in the LAYER#_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 additional keyword, LAYER#_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
The baffles (vertical structural panels perpendicular to the nozzle axis) are defined by specifying the number and material used with the BAFFLE keyword, along with definitions of normalized x-coordinate location, thickness and height. By default, currently baffle heights are resized to mate with the external aircraft geometry which is hard-coded in MULTI-F, so the provided height values are ignored. An example baffle specification is below:
BAFFLES= (6,PANEL)
BAFFLES_LOCATION= (0, 0.2, 0.4, 0.6, 0.8, 1)
BAFFLES_THICKNESS= (0.01, 0.01, 0.01, 0.01, 0.01, 0.01)
BAFFLES_HEIGHT= (0.2, 0.2, 0.2, 0.2, 0.2, 0.2)
BAFFLES_DV= (0, 1, 2, 3, 4, 0, 5, 6, 7, 8, 9, 10, 0, 0, 0, 0, 0, 0)
where 6 baffles are defined using the PANEL material. The BAFFLES_DV keyword is used to specify which baffle locations, thicknesses, and heights are design variables, in that order. See the design variables page for more information.
The stringers (long thin members running the length of the nozzle) are defined by specifying the number and material used with the STRINGERS keyword. Currently a piecewise-linear geometry is assumed for both the stringer thickness (circumferential direction) and height (radial direction). The stringer thickness and height geometry definitions share the same non-dimensional break locations which are specified in the STRINGERS_BREAK_LOCATIONS keyword. Height and thicknesses are defined in the vectors provided with the STRINGERS_HEIGHT_VALUES and STRINGERS_THICKNESS_VALUES keywords. A STRINGERS_DV keywords can be provided to specify which break locations, height values, and thickness values are design variables, in that order. See the design variables page for more information.
It is common to specify that the stringers height coincides with the baffle height. In this case the BAFFLES_LOCATION string can be provided instead of a vector for the STRINGERS_BREAK_LOCATIONS keyword and the BAFFLES_HEIGHT string can be provided instead of a vector for the STRINGERS_HEIGHT_VALUES keyword. In this case, STRINGERS_DV should not be specified.
An example stringer parameterization is:
STRINGERS= (4,GR-BMI)
STRINGERS_BREAK_LOCATIONS= BAFFLES_LOCATION
STRINGERS_HEIGHT_VALUES= BAFFLES_HEIGHT
STRINGERS_THICKNESS_VALUES= (0.01, 0.01, 0.01, 0.01, 0.01, 0.01)