Wheel Geometry


This section covers information required for the wheel assembly: wheels, RRF internal faces, and contact patches/plinths.

Contents of Page:

Wheel Geometry Required Information

The wheel geometry has unique attributes for axis, origin, position, and radius. The user must enter all of these parameters when uploading wheel parts. The app interface for a wheel is shown in Image 1.

All wheels should define the axis of rotation with a negative Y component so that they are rotating in the same direction as the road would be moving.

The origin should be set at the center of the wheel. It is important for calculating the front to rear and left to right downforce and lift balance forces of the vehicle.

The radius is the linear distance from the origin to the outer circumferential edge of the tire. There are four wheel positions and the user should have a wheel for each position.

These attributes need to be defined for each wheel file uploaded.

Image 1: TS AUTO APP interface for wheel part details

There are four wheel positions which have named abbreviations as shown below. All references are from the drivers perspective. Select the correct wheel position for each part from the drop down bar.

Image 2: Wheel position nomenclature

Image 3: Wheel position selection

Wheel Origin and Radius

The following method should be used for extracting the rolling radius from tyre without a plinth. This methods uses ANSA but a similar technique could be used with Hypermesh or any CAD package.

Image 10: Wheel Assembly

Image 11: Curve Creation

1. Create arcs on the inboard and outboard faces of the wheel rims.

Image 12: Intersection curve between front and rear face

2. Create a curve from the inboard and outboard curve origins. Create a midpoint between the inboard and outboard origins. This midpoint will be the origin of your wheel.

Image 13: Contact patch free plane

3. Create a free curve between the front and rear of the tire centered at the wheel origin. The free curve needs to intersect the contact patch plane. Subdivide the curve into two. The distance between the wheel origin and free curve will be the rolling radius.

Wheel Axis

All wheels have axis of rotation with a negative Y component to ensure that they are rotating in the same direction as the road would be moving. Don’t make the mistake of having the left wheels using the opposite axis relative to the right wheels. The axis corresponds to the right-hand rule of rotation. If one were to make a thumbs-up with the right hand, when the thumb is pointed in the positive direction of the axis, the curl of the fingers would indicate the direction of positive rotation.

Image 14: Wheel and rotational axis

Axis Determination

Using the curve between the rear and front faces and wheel origin, create when determining the radius the axis for the wheels can be created. Select the wheel origin and move the point along the curve by one unit. The distance between these two points will be your rotational axis. Ensure that the direction of the axis is correct using the method described above.

Image 15: Rational axis determination

Rotating Reference Frame

Rotating reference frame regions, or RRFs, are completely sealed volumes that are enclosed by 2 or more simple surfaces called internal faces. The purpose is to isolate rotating parts that have features similar to spokes, fan blades or paddles so rotational momentum can be added to the airflow near these parts. Rotating reference frames require inside points and the section below outlines one way to obtain the inside point.

Image 16: RRF internal faces

Creation of RRF Internal Faces

Some general guidelines for the creation of RRF internal faces:

  • The RRF internal faces must be rotationally symmetric about the wheel axis
  • When possible, simple planar surfaces should be used
  • Non-rotating geometry such as calipers, brake pads and brake hoses should not be contained inside the rotating reference frame.
  • It is recommended that only rotating parts are contained within the RRF internal faces
  • You must ensure that the RRF internal faces volume is completely sealed. If it is not sealed then the volume of fluid will not be separated.

Inside Point

RRF internal faces requires an inside point. The inside point is a reference point between the RRF internal faces and outside any geometrically closed volumes.

These points must be outside of any geometry such as wheel spokes, fan blades or hubs, i.e., they must be in free air. If they are in a location that would not be visible to the naked eye on a production part, it likely is not a valid point location

Image 17: RRF internal faces and inside point

An example on the determination for the inside point is depicted below through images 19-20. When picking an inside point ensure that the point is between the RRF internal faces and outside any geometrically closed volumes. It is important to note that this inside point must not be coincident with the faces of any geometry passing through the RRF internal faces.

To determine the inside point if a trye with planar RRF internal faces, the area between the wheel spokes is an ideal space for the inside point. The area between the spokes is sufficient since the inside point will be out of range of any moving parts and not too close to the RRF internal faces.

Image 18: Planar RRF internal faces (left) and center slice of wheel and RRF internal faces

Image 19: Select three points in the wheel spoke region

1. If the geometry has a clean edge in the wheel spoke region, create a center of gravity point using that curve. If curve path is not clear select 3 points each at located at the largest radii.

Image 20: RRF inside point

2. Using a center of gravity feature, create a midpoint from the 3 points in step 1. This center of gravity point will be the inside point for the RRF internal faces. Image 20 shows that the inside point is in mid air and out of range of any moving parts.

Contact Patch

A contact patch is a planar surface at the bottom of the wheel that is in contact with the road. A plinth is a surface vertically extruded from the wheel's contact patch. A wheel modeled without a plinth tends to have a low quality region where the tire touches the ground. Using a plinth creates a more consistent interface with the ground and improves modeling performance.

TotalSim's App follows the best practice of modeling the vehicle with plinths. If the user has plinths created, they should be uploaded as a second part of the wheel. If plinths are not user created, TS AUTO has the capability to generate plinths for any vehicle.

Image 21: Wheel and plinth assembly in regards to the ground pane

Image 22: Contact patch and plinth

Secondary Rotating Parts and RRFs

If the wheels rotors have flow passing through, it is possible for the rotors to have their own RRFs covering the holes that allow for flow passage so that the pumping effect is captured for a spinning rotor. It is not always necessary for the wheel rotor to have RRFs. If the rotor is separated from the wheel it can be uploaded as an separated part type, "WheelSub". If a seconday wheel part is uploaded, a RRF is not needed for the simulation to run. If a wheel rotor is uploaded only, the position is need for the part details, while if a RRF for the secondary wheel part is uploaded, the user must provide the position and an inside point.

Image 23: Wheel rotor geometry

Image 24: TS AUTO APP geometry types