VORTEX [GENERATOR] {MODEL WENDT ZONE iz1 BOUNDARY {I1 | IMAX | J1 | JMAX | K1 | KMAX} \ [SUBSET I range J range K range] ZONE iz2 BOUNDARY {I1 | IMAX | J1 | JMAX | K1 | KMAX} \ [SUBSET I range J range K range] NUMBER ival vg_boundary {XLOC xl | YLOC yl | ZLOC zl} chord height alpha \ [VEL vmax] [DEL delta] | MODEL BAY ZONE izone NUMBER ival VANE_SPEC imin imax jmin jmax kmin kmax vg_boundary alpha area \ [model_constant]} ENDVORTEX |
This keyword block is applicable to three-dimensional cases with
structured grids, and enables the user to specify the effects of vortex
generators in the flow using a choice of two models:
The Wendt model
The various elements of the VORTEX GENERATOR input block are
defined as follows:
VORTEX [GENERATOR] |
Defines the beginning of the vortex generator keyword input block.
ENDVORTEX |
Ends the vortex generator input block.
{MODEL WENDT | MODEL BAY} |
The main part of the VORTEX GENERATOR block is divided into two sections, corresponding to input for the Wendt and BAY models. Either MODEL WENDT or MODEL BAY must be specified, but not both.
Wendt Model
The Wendt model uses a discontinuous change in secondary velocity across a zonal interface boundary in order to simulate the vortices produced by an array of vane-type vortex generators. The model determines the strength of each vortex based on the generator chord length, height and angle of incidence with the incoming flow, as well as the incoming flow core velocity and boundary layer thickness. Each vortex center is placed at the grid point closest to the location determined by the user-specified generator location on the boundary, and the generator height.
Note that the Wendt vortex generator model is derived from experimental data taken at axial stations which were one chord length downstream of the trailing edge of the generators, and therefore the secondary velocities produced by the model simulate vortices at this station, rather than at the generator trailing edges. For most accurate results, the boundary where the vortex generator boundary condition is applied should be at this one chord length station.
The following restriction applies:
The elements of the VORTEX GENERATOR input block applicable to
the Wendt model are defined as follows:
ZONE iz1 BOUNDARY {I1 | IMAX | J1 | JMAX | K1 | KMAX} \ [SUBSET I range J range K range] ZONE iz2 BOUNDARY {I1 | IMAX | J1 | JMAX | K1 | KMAX} \ [SUBSET I range J range K range] |
These two lines define the location of the vortex generator array. The relevant zones are given by the values of iz1 and iz2, and the relevant boundaries within zones iz1 and iz2 are specified via the BOUNDARY keyword parameter.
iz1 | The "upstream" zone. The secondary velocities will be increased when passing information from this zone to iz2. | ||
---|---|---|---|
iz2 | The "downstream" zone, i.e., the zone receiving increased secondary velocities from zone iz1. Secondary velocities will be decreased when passing information from this zone back to zone iz1. |
Note that the secondary velocity is the flow in a plane normal to the primary velocity. For example, for a vortex generator array at an i-interface boundary, the primary flow is in the i direction, and the secondary velocity is in the j and k directions.
The SUBSET parameter may be used to specify that the change in secondary velocity occurs only over a part of the zone boundary. Otherwise, it is assumed that the change occurs over the entire boundary. The range parameters define the part of the zone boundary over which the change occurs, and take one of the following forms:
index1 index2 | Starting and ending indices in the specified direction. LAST may be used for the last index. | ||
---|---|---|---|
ALL | Equivalent to 1 LAST. |
The starting and ending indices for the appropriate I,
J, or K parameter (depending on the boundary
specified) must be the same, and correspond to that boundary.
NUMBER ival |
This defines the number of vortex generators in the vortex generator
array (i.e., on the specified boundary).
vg_boundary {XLOC xl | YLOC yl | ZLOC zl} chord height alpha \ [VEL vmax] [DEL delta] |
Defines the location and geometric parameters of each vortex generator. A separate line of input must be included for each generator.
vg_boundary | The minimum or maximum index, specified as IM, IX, JM, JX, KM, or KX, within the specified boundary surface (as specified by ZONE and SUBSET) where the generator is mounted. This boundary must have been defined as a viscous wall. As an example, for a vortex generator array at an i-interface boundary, either JM, JX, KM, or KX should be specified, where JM means the generator is at the j = 1 interface boundary, JX means it's at the j = j_{max} boundary, etc. | ||
---|---|---|---|
XLOC, YLOC, ZLOC | xl, yl, or zl is the x, y, or z coordinate location in inches of the base of the vortex generator on the already specified boundary surface and wall boundary. (Currently, only one coordinate direction and location may be specified. This may lead to ambiguity in specifying the locations for generators placed in complex duct geometries. This shortcoming will be addressed in future code updates.) | ||
chord | The chord length of the vortex generator in inches. Must be greater than zero. | ||
height | The height of the vortex generator in inches. Must be greater than zero. | ||
alpha | The angle of incidence of the generator in degrees. Must be non-zero. More specifically, it is defined as the angle the generator chord line makes with the primary flow direction. The sign of alpha is determined using the "right-hand rule" of vector mechanics. For a given generator, use a normal vector pointing into the wall (the thumb), and the primary flow direction (fingers). If the rotation from the primary flow direction towards the generator follows the right-hand rule, then the sign of alpha is positive. Otherwise, it is negative. A positive value of alpha generally results in a vortex with a counterclockwise rotation, and conversely. The recommended range of magnitudes for alpha is between 8 and 20°. | ||
VEL | vmax is the maximum velocity at the vortex generator station, in ft/sec. The default is for Wind-US to compute this value from the flow. It is currently recommended that this value be specified by the user. Must be greater than zero. | ||
DEL | delta is the boundary layer thickness of the incoming flow, in inches. The default is for Wind-US to compute this value from the flow. It is currently recommended that this value be specified by the user. Must be greater than zero. |
In selecting values for the above described parameters, keep in mind that the vortex generator model was derived from conservation of momentum and inviscid theory, correlated with experimental data having height/chord ratios between 0.13 and 2.62, height/delta ratios between 0.12 and 2.60, and for duct flows with core Mach numbers ranging from 0.20 to 0.60. Because of the theory used in its derivation, the model is intended to work well outside of the range of the experiments. However, there is one caveat: past experience indicates that the model does not work when the vortex generators are placed in regions of sonic flow.
Example
The following example illustrates the use of the Wendt vortex generator model for one vortex generator array located between zones 2 and 3. The interface between zones 2 and 3 corresponds to the i_{max} boundary of zone 2 and the i_{1} boundary of zone 3. The array contains two vortex generators, both mounted on the j_{max} viscous wall boundary of the zone interface with z coordinate values of −0.52 inches and 0.52 inches. The generators have the same geometric parameters: the chord length is 1.6 inches, the height is 0.4 inches, and the angle of incidence is 16°.
VORTEX GENERATOR MODEL WENDT ZONE 2 BOUNDARY IMAX ZONE 3 BOUNDARY I1 NUMBER 2 JX ZLOC -0.52 1.6 0.4 16.0 JX ZLOC 0.52 1.6 0.4 16.0 ENDVORTEX
See Also: BOUNDARY TVD
BAY Model
The BAY model is a source term model which models the side force produced by the vortex generator and adds it to the momentum and energy equations. This side force automatically adjusts its strength based on the local flow. The user specifies the grid points over which the force is to be applied (i.e., enclosing each vortex generator).
The elements of the VORTEX GENERATOR input block applicable to
the BAY model are defined as follows:
ZONE izone |
This line defines the zone containing the vortex generator array.
NUMBER ival |
This defines the number of vortex generators in the vortex generator
array.
VANE_SPEC imin imax jmin jmax kmin kmax vg_boundary alpha area [model_constant] |
This keyword line must be specified ival times, i.e. once for each vane. It is used to specify the grid points over which the model acts for each vane and the accompanying vane angle of incidence, planform area and model constant. These parameters are described in more detail below.
imin, imax | Minimum and maximum i indices defining the grid region enclosing the vortex generator | ||
---|---|---|---|
jmin, jmax | Minimum and maximum j indices defining the grid region enclosing the vortex generator | ||
kmin, kmax | Minimum and maximum k indices defining the grid region enclosing the vortex generator | ||
vg_boundary | The minimum or maximum index, specified as IM, IX, JM, JX, KM, or KX, indicating the viscous wall where the generator is mounted. Here JM means the vane is on the j = 1 boundary, JX means it's on the j = j_{max} boundary, etc. | ||
alpha | The angle of incidence of the vane chord line (in degrees) with respect to the coordinate grid line in the primary flow direction. Note: In instances where the leading edge of the vane corresponds to the maximum index of the VANE_SPEC range rather than the minimum (i.e., jmax or kmax approximately specify the leading edge of the vane), the sign of the angle must be negative in order to produce the correct directional rotation of the vortex. | ||
area | The vane area (in^{2}) | ||
model_constant | The model constant. The default value is 10. |
Example
The following example illustrates the use of the BAY vortex generator model for one vortex generator array located in zone 2. The array contains two vortex generators, both mounted on the j_{max} viscous wall boundary. The VANE_SPEC values of the zones are shown below. They both act over the same i and j indices but at different k indices on the wall. Both generators have the same angle of incidence with the primary flow direction grid line, 16°, and have planform areas of 0.21 in^{2}.
VORTEX GENERATOR MODEL BAY ZONE 2 NUMBER 2 VANE_SPEC 15 25 45 65 20 25 JX 16.0 0.21 VANE_SPEC 15 25 45 65 35 40 JX 16.0 0.21 ENDVORTEX
Last updated 1 Apr 2016