6. RESULTADOS Y DISCUSIÓN
6.3. Aspectos moleculares y estructurales
6.3.1. Calorimetría de barrido diferencial
The geometry data file includes sections of text lines that help you to identify the parameters defined here.
You should read the section on geometry in Appendix A: A Note on Sign Convention for Angles and Velocit-ies (p. 127) to become familiar with sign conventions and angle definitions used in this file. An example of a geometry data file is given in Appendix C: Example of a Geometry Data File (*.geo) for a Radial Impeller (p. 130).
Section 1: Character strings identifying the geometry data (max 72 characters/line) The syntax is:
Character string - title(1) Character string - title(2) Character string - title(3)
Section 2: Number of quasi-orthogonal lines and scale factor (one line) The syntax is:
n_qo scale
Description Parameter
n_qo = number of quasi-orthogonal lines from inlet to outlet of the domain. From version V1.31 onwards the maximum value of this parameter is unlimited.
n_qo
The scaling factor for all geometry data that is input.
scale
Screen Output Files (screen.scn)
Description Parameter
• Usually the geometry data is input in SI units (that is, all values are expected in m and not mm) and then this value is 1.0.
• If the input geometry data comes from a CAD system then it may be in mm. In this case, the value of scale must be 0.001. Similarly the value can be adjusted to allow the geometry data to be input in other systems of units;
for example, inches.
• This scale factor only scales the data in the geometry input file and has no effect on other dimensions elsewhere; for example, it does not scale the reference diameter, which must be input with units of metres, in the aerodynamic file.
• If you specify scale = 0.0, unity is used.
For each quasi-orthogonal, the following data is required to define the flow channel for the meridional through-flow calculation and the meridional spacing of the quasi-orthogonals. Note that some of this data is also repeated in the section on the blade geometry. This duplication allows calculations to be made in a channel that is not the same as the hub and casing line of the actual blade definition (blade cropping).
Section 3: Definition of quasi-orthogonal types and end points (n_qo lines: i = 1 to n_qo) The syntax (of a single line) is:
i r_hub(i) r_shr(i) z_hub(i) z_shr(i) n_blade(i) n_curve(i) i_type(i) i_row(i) i_spool(i)
Description Parameter
Number of a particular quasi-orthogonal line.
i
Notes:
• The actual value is not used by the program internally because it recounts the quasi-orthogonals as they are in-put. The number specified is only used as a guide to the location in the input file.
• This allows you to merge two different geometry files of, say, a rotor and stator, to a single stage geometry file without the need to renumber the quasi-orthogonals. In this case, the same number may appear more than once.
In a similar way, a single quasi-orthogonal may be re-moved without the need for renumbering the lines.
Radial coordinate at hub end of quasi-orthogonal [m].
r_hub(i)
Radial coordinate at casing end of quasi-orthogonal [m].
r_shr(i)
Axial co-ordinate at hub end of quasi-orthogonal [m].
z_hub(i)
Axial co-ordinate at casing end of quasi-orthogonal [m].
z_shr(i)
Notes on co-ordinates:
• r_hub may not be close to zero; adapt the grid if neces-sary to avoid small values of r_hub.
Description Parameter
• The aspect ratio of the quasi-orthogonal lines determines the stability of the solver. The lines should not be too closely spaced.
• The end coordinates of the leading and trailing edges of blade rows should be included in the list of coordinates.
• The end coordinates of the leading edge of a splitter vane should be included in the list of coordinates.
Number of blades in blade row.
n_blade(i)
Notes:
• = 0 in duct regions.
• The number of blades changes at a splitter blade leading edge in a compressor or at a splitter vane trailing edge in a turbine, and changes again for multiple splitters. This is the only information that the program has about the splitters, so the location of the splitter vane leading or trailing edge needs to be a quasi-orthogonal line in the input data.
Number of defining points along the ith quasi-orthogonal line.
n_curve(i)
Notes:
• = 1, a special case for duct stations. This indicates that there are 2 defining points (as for n_curve(i) =2) but that no further information for this calculating station is provided in section 4 below, because it is already fully defined by the hub and casing points given in section 3.
• = 2 for a linear calculating plane in which only the end points of the quasi-orthogonal are defined. In this case, similar information can be found in section 4.
• > 2 for a non-linear or curved calculating plane.
• The number of defining points can vary from station to station but n_curve(i) should typically be the same for all stations because streamline section data is usually available on a fixed number of spanwise sections.
• Note that the hub and casing geometry information does not necessarily have to be the same as that defined in section 4. In this case the data in section 3 will be used to crop the blade row or to make a section through the blade information in section 4.
Parameter to identify type of calculating station:
i_type(i)
1 - for duct region
2 - for non-rotating blade row (stator)
Screen Output Files (screen.scn)
Description Parameter
Notes:
• The program internally identifies which lines are leading and trailing edges from the changes of type of blade row, and which line is the leading edge of a splitter vane (by the change in blade number).
• There must be at least two duct calculating stations up-stream of the first blade row, and downup-stream of the last blade row.
• A blade row must consist of at least two calculating sta-tions (leading and trailing edge). Typically a radial impeller will have around 15 calculating stations, because this gives a 6° turn between each station and improves the calculation of the curvature terms.
• There must be at least two blade calculating stations up-stream and downup-stream of a splitter vane leading edge.
• Other types of blade row may be defined at a later stage.
This parameter is used to identify type of blade row and stage of the quasi-orthogonal calculating station. In fact the pro-i_row(i)
gram can usually identify the type of blade row itself from the geometry and the context, so it is not necessary to specify these values at all and, in the first instance, this parameter may be set to zero. They are included here for special cases where the program may have difficulty with the rules that are coded to identify blade row types.
= n11 - radial compressor inlet guide vane1
= n12 - radial compressor inlet guide vane2
= n13 - radial compressor impeller blade
= n14 - radial compressor diffuser vane
= n15 - radial compressor return channel vane
= n16 - radial compressor axial de-swirl vane
= n21 - axial compressor inlet guide vane1
= n22 - axial compressor inlet guide vane2
= n23 - axial compressor rotor blade
= n24 - axial compressor stator vane
= n25 - axial compressor outlet guide vane
= n31 - radial turbine inlet guide vane1
= n32 - radial turbine inlet guide vane2
Description Parameter
= n33 - radial turbine impeller blade
= n34- radial turbine stator vane
= n35- radial turbine outlet guide vane
= n41 - axial turbine inlet guide vane1
= n42 - axial turbine inlet guide vane2
= n43- axial turbine rotor blade
= n44- axial turbine stator vane,
= n45- axial turbine outlet guide vane Notes:
The value of n determines which stage is being considered, such that a multistage axial compressor with an IGV would begin with values of 121 for the inlet guide vane, continue with values of 123 for the rotor, and 124 for the downstream stator, so that the next rotor would be 223, an so on. A double row of stators would be denoted as n24 and n25 for the successive blade rows.
Parameter to identify rotational speed of spool or shafts where different blade rows have different speeds.
i_spool
0 single shaft with one speed (ref_n) 1 first shaft with speed (ref_n1)
2 second spool with second speed (ref_n2) 3 third spool with third speed (ref_n3)
Note that counter-rotating blade rows can be dealt with by specifying negative speeds for the second spool. The program determines the number of different spools (n_spool) from the number of different values of i_spool(i) found in the geometry input file. (The maximum is set to be 3.)
Notes:
• The data is supplied on n_curve lines spaced fairly evenly from hub to casing. For example, if n_curve = 5, there may be points at 0%, 25%, 50%, 75%, and 100% of span. If n_curve = 2, there will be just two points, at 0% and 100% span.
• The blade data and quasi-orthogonal data in section 4 may extend outside of the flow channel defined by the meridional coordinates given in section 3. In a normal calculation, the data overlaps partly with that given in section 3, because the end points of the quasi-orthogonal lines are defined twice (except for duct calculating stations with n_curve(i) = 1; see above). The flow channel defined in section 3 is generally congruent with the blade hub and shroud defined in section 4. The
Screen Output Files (screen.scn)
allows a calculation to be made in a cropped or trimmed flow channel only by changing the data in section 3; section 4 does not need to be changed.
• The end points of the quasi-orthogonal lines, as defined by coordinates r_hub(i),r_shr(i), z_hub(i), and z_shr(i), should lie along the quasi-orthogonal lines as defined by r_qo (j,i) and z_qo(j,i) below. In many cases, the end points will be coincident with the blade data, but if this is not the case, it is not acceptable to define end points that do not lie on the blade data point.
• All the angles are specified in degrees because this is more convenient in those cases where it may be necessary to define the geometry by hand, and also allows a simple consistency check, but in-ternally the program converts them into radians. Further description of the angles is provided in Appendix A: A Note on Sign Convention for Angles and Velocities (p. 127).
The sections above define only the hub and casing walls and provide information on the type of calculating station. The detailed orientation and position of the curved quasi-orthogonal line and the details of the blade surface geometry are provided in the next section.
Section 4: Geometry of quasi-orthogonal line and blade The syntax (of the single line) is:
i j r-qo(j,i) theta_qo(j,i) z_qo(j,i) thu_qo(j,i) gamma_r_qo(j,i) gamma_z_qo(j,i)
Description Parameter
Number of a particular quasi-othorgonal for data input (in-creasing from inlet to outlet). Note that this value is not read i
in as input data but is simply used as orientation in the data file when examining the geometry input data.
Number of streamline for data input (increasing from hub to shroud). Note that this value is not read in as input data but j
is simply used as orientation in the data file when examining the geometry input data. Note that for each q-o (i), the spanwise data is entered (j) before continuing with the next q-o.
Radial coordinate of point j along q-o (i) [m].
r_qo(j,i)
Circumferential coordinate of blade camber line at point (r_qo,z_qo) [degrees].
theta_qo(j,i)
Note:
• The angular coordinate (theta) is taken as positive in the direction of rotation and negative in the other direction.
• In a duct region this angle may be zero.
• This angle is not used by the program but helps to visu-alize the blade shape and may be useful for plots of the blade shape.
• In a region where there is a splitter vane this angle is the blade camber angle of the main blade and not of the splitter.
Axial coordinate of point along quasi-orthogonal [m].
z_qo(j,i)
Circumferential thickness of blade at point (r_qo,z_qo) [m].
thu_qo(j,i)
Description Parameter
Note:
• In a duct region this thickness should be specified as zero.
• In a region where there is a splitter vane this thickness is the mean thickness of the main blade and the splitter.
• At leading and trailing edges the value supplied is not used by the program, but the calculating station is taken to be at the limit of the chord with zero thickness.
• The thickness is not the thickness normal to the camber line.
Lean angle of the blade with a radial line [degrees] as defined in Appendix A: A Note on Sign Convention for Angles and Velo-cities (p. 127).
gamma_r_qo(j,i)
Lean angle of the blade with an axial line [degrees] as defined in Appendix A: A Note on Sign Convention for Angles and Velo-cities (p. 127).
gamma_z_qo(j,i)
Notes:
• This geometry includes the coordinates of the blade camber surface (r-qo(j,i),theta_qo(j,i), z_qo(j,i)) so that it would theoretically be possible for the program to differentiate this inform-ation to determine the slope angles of the surface (gamma_r_qo(j,i),gamma_z_qo(j,i)).
This is not done for two reasons. Firstly, experience shows that with the crude grids typically used for throughflow calculations, this differentiation would be an unwanted source of error leading to poor estimates of the blade angles, so a system was chosen in which the blade angles are supplied.
In fact the value of theta_qo(j,i) is not used by the program and can be specified as zero.
Secondly, in many cases the slope angles of a blade row are known (inlet and outlet angles) whereas the circumferential coordinate is unknown.
• This system of geometry with the definition of two angles is designed for radial turbomachinery applications because it allows the complex shape of three-dimensional blades to be defined by the use of the two lean angles,gamma_r and gamma_z.
• In conventional axial turbomachinery throughflow programs, it is not usual to define the blade in much detail because often simulations are carried out with only inlet and outlet blade angles. This is also possible with Vista TF. In a ductflow calculation with only leading and trailing edges, the value of gamma_r can be set to 0°. Because the leading and trailing edges are not considered to have any blade force, this has no effect on the simulation. The value of gamma_z defines the inlet and outlet blade angles of sections through the blade at constant radius.
• Vista TF assumes that the geometry is always specified for a clockwise rotation (see Appendix A: A Note on Sign Convention for Angles and Velocities (p. 127)). If the geometry is correctly specified, a negative rotational speed is used, and Vista TF performs calculations assuming that the shaft is ro-tating in the wrong direction with all the wrong incidences, loading, an so forth. For the case where the geometry is specified for counterclockwise rotation, the value of i_flow in the .con file should be specified as a negative number, for example, -1 or -2. This causes the program to internally switch the angles from positive to negative, and vice-versa, before it proceeds to perform calculations as usual, assuming that the shaft rotates in the clockwise rotation.
• The next sections provide additional blade-row geometry data for use by the correlations in the program. Although this data is not always needed, the format of this section includes 8 real
para-Screen Output Files (screen.scn)
Section 5: Additional geometry data (n_curve(i) lines for each blade row) The syntax is:
j throat throat_pos clearance max_thickness te_thickness dummy dummy dummy
Description Parameter
Number of a particular streamline for data input (increasing from hub to shroud).
j
Throat width of section j [m].
throat
Note:
• If the value of zero is input then the program estimates the throat width from the blade angles and the blade thickness, taking into account that the throat is close to the leading edge for compressors and close to the trailing edge for turbines. For radial compressors this estimate is not particularly accurate and for cases close to choke you should provide more precise data here.
• For axial compressors it is assumed that the blade has a circular arc camber line and the program includes an es-timate of the throat area based on the geometrical rela-tionships for circular arc blades.
• For other blade types, you should specify the value.
Position of throat on this blade section.
throat_pos(i)
Note:
• If the value of zero is input then the program estimates the throat position from the blade angles and the blade thickness, taking into account that it is close to the leading edge for compressors and close to the trailing edge for turbines.
• For radial compressors this estimate is not particularly accurate and for cases close to choke you should provide more precise data here.
• For axial compressors it is assumed that the blade has a circular arc camber line and the program includes an es-timate of the throat position based on the geometrical relationships for circular arc blades.
• For other blade types, you should specify the value.
Tip clearance of hub section [m].
tip clearance
Tip clearance of shroud section [m].
hub/shroud
Note:
• If the first value is non-zero, this is interpreted as the hub clearance.
• If the last value (n_curve(i)) is non-zero, this is inter-preted as the casing clearance.
Description Parameter
• In a variable stator vane with a hub clearance and a clearance gap for the shaft, it is possible to have non-zero values on both the hub and the tip and then both will be taken into account in the loss correlations.
Maximum normal thickness of blade section [m].
max_thickness
Note:
• Although the circumferential thickness of the blade row is already specified in section 3, the location of the quasi-orthogonal lines may not coincide with the location of normal maximum thickness, so this value must be spe-cified separately.
• If the value of zero is specified then the program searches for the normal maximum thickness of the blade, as given in section 3, and uses it.
Trailing edge normal thickness of blade section [m].
te_thickness
Note:
• Although the circumferential thickness of the blade row is already specified in section 3, this value must be spe-cified separately.
• If the value of zero is specified then the program estimates the trailing-edge thickness of the blade from the circum-ferential thickness given in section 3, and uses it.
In order to allow for parameters that may be needed by other correlations in the future, the program includes three dummy parameters which should each be set to 0.0.
dummy