Automotive Model Mounting
General Mounting Information
A vehicle ground plane is available for automotive model testing. The all-aluminum ground plane occupies the entire test section and has fairings that extend into the bellmouth and diffuser. The model mounting structure is isolated from the wind. Two multiple-point mounting systems are available for testing either heavy duty trucks or passenger vehicles. Each mounting system is concealed with the use of coverplates. A large turntable moves is synchronized so that rotates in conjunction with the model as it is yawed. The approximate test section size with the ground plane installed is 12-feet wide, 7-feet tall, and 15-feet long.
Front view of vehicle ground plane configured for 20% heavy-duty truck testing (6 post mounts)
A specialized car mounting apparatus is available for supporting a car model by four points. A car model is typically supported by some type of connection at each wheel, such as a post that enters up through the coverplate and into the center of the wheel.
The car mounting apparatus consists of an aluminum plate with two precision glide rails attached to each side of the plate. These rails support two fixtures: one for mounting the front wheels, one for mounting the rear wheels. The aluminum plate attaches to an adapter block that fastens to the external balance.
A lead-screw adjusts the fore/aft position of the front wheel mounting fixture. Another lead-screw adjusts the fore/aft position of the rear wheel mounting fixture.
The front and rear mounting fixtures are identical. Each fixture supports two steel mounting blocks. By adjusting a single screw, the mounting blocks move equidistant from the center of the beam allowing for variation of the track distance. A millimeter ruler attached to the fixture allows one to set an exact track distance between the two blocks.
Each block has been designed for handling a variety of mounting options. Currently, two mounting options have been fabricated for use with the car mount:
1. A 3-inch diameter pad with a 0.375-inch diameter post which protrudes up into the wheel of a car model
2. A threaded-rod mount that allows for ½-13 threaded posts to protrude up into the wheel of a car model
The following ranges of mounting positions can be set using the car mounting system:
Wheelbase and Track Positions for Car Mount
A total wheelbase of 58-inches can be accommodated without the use of adapters. The minimum wheelbase is 6-inches but could be smaller using adapters. The entire car mounting beam can be installed backwards if more travel is needed for the mounting of the front wheel.
Side view of 20% Volvo S60 car model
A 116-inch long aluminum beam is used to provide support for a six-point mounting system for 20% heavy-duty truck models. The beam width is 12-inches. Three aluminum cross-beams support the wheel mounting posts at the three axle locations. The rear four posts are fixed in position. The front two wheel mounting posts are on precision glide rails allowing for 35-inches of travel. The model geometry should be fixed so as to prevent the front wheels from moving during testing.
Truck mounting beam with six-point model attachment
Center-to-center distance for front wheel posts is 15.75-inches, mid-wheel posts is 17.25-inches, and rear wheel posts is 18.25-inches.
Side view of 20% Kenworth T2000 heavy-duty truck model
The center channel opening in the turntable is 27-inches wide and 124-inches long. The center channel opening is covered with coverplates. Two styles exist: clamp-down and screw-down.
The clamp-down coverplates come in a variety of sizes to allow for the filling of gaps. The larger coverplates have front and rear facing lips to interlock for reducing flow-through the ground plane. Available sizes of coverplates include: 0.125, 0.25, 0.5, 1, 2, 2.75, 3, 3.75, 5, 5.75, 11.75 inches.
Two specialized coverplates are available for the area where the mounting connections protrude through the ground plane surface and attach to the model. Each coverplate consists of a metal frame with two 11.5-inch diameter plastic disks. Each disk contains a 3-inch diameter hole that can be filled with a spacer to reduce the hole size to 0.75-inches. The two disks are geared so that they can be turned to locate the 3-inch diameter holes equidistant from the center of the coverplate.
Boundary Layer Suction System
The boundary layer height can be reduced through the use of suction on a porous plate located 80.5-inches ahead of the test section center (and turntable center). A 20-hp blower sucks the air through the porous plate, into a plenum, and then exhausts the air outside of the wind tunnel. The porous suction plate is 74-inches wide and 14-inches long and has a 10% porosity using holes of 0.127-inch diameter. The porous suction plate is flush with the ground plane surface.
A boundary layer rake and five-hole probe were used to measure the flow qualities in the test section with boundary layer suction operational. The suction system was designed to be able to add a secondary blower to provide more suction if necessary at a later date.
Up/Downstream Distribution of Displacement Thickness with
Boundary Layer Suction (-X is upstream, X=0 is test section center)
Left/Right Distribution of Displacement Thickness with
Boundary Layer Suction (-Y is left, Y=0 is test section center)