Pressure Scanning in Aerodynamics – A Winning Formula
Race car aerodynamic optimisation continues to become more important in the search for performance advantage. A major part of a team’s budget is invested in enhancing and improving the aerodynamic performance of the car and a large team of aerodynamic specialists and facilities are employed in achieving this. Aerodynamic efficiency is a major contributor to a winning car. It is often said that a reduction in drag is less costly and easier to achieve than a weight reduction or a power increase. It is paradoxically challenging for the engineer to attain huge levels of downforce to enhance cornering performance without compromising car forward speed by increasing drag.
Stringent regulations governing car shapes and sizes leaves the aerodynamicist considering every part in order to reduce drag and gain competitive advantage. Front and rear aerofoils, or wings, together with the bodywork surface push the car down to the road surface. Under the car, complex venturi shapes increase air velocity, creating a low-pressure “suction” effect, with minimal cost of drag. Winglets and other devices are fitted, in addition to the front and rear wings, to condition the flow for downstream aerodynamics, or directly generate downforce effects themselves.
This leads to highly-creative design shapes and ever-more complex air flow analysis. CFD (Computational Fluid Dynamics) becomes the prime tool for calculating airflow performance, but this is not enough. The data must be validated with extensive Wind Tunnel testing, as well as on-car testing, where possible. These three major forms of testing triangulate to gather useful data for analysis.
Where wind tunnel testing is utilised, a highly-detailed scale model (usually 60% scale) is constructed representing the full-size car. The model is installed in the wind tunnel, on a rolling road, to simulate moving ground effects, and subjected to extended testing over a wide range of wind velocities and directions, often up to 100 m/s. Data is gathered from numerous locations on the model to map the overall aero performance and identify any areas that require further analysis or evaluation. The model is supported from a multi-axis balance which measures the drag forces on the model very accurately and with great sensitivity.
The Measurement Challenge
Since the sport’s ruling body limits the amount of wind tunnel time allowed, the challenge is to collect accurate meaningful data and make every second of “wind-on” test-time count. The challenge for the engineer is to gather as much data as possible in the available time and to be able to quickly develop modifications to the model to install and validate improvements.
Typical models are fitted with numerous small pressure tappings that allow the localised pressure to be measured at a multitude (often many hundreds) of points on the aerodynamic surfaces. These tubes connect directly to the in-model pressure scanners for conversion to pressure measurements which are then time-stamped, synchronised and communicated to the computer systems via Ethernet or similar communications for mapping and further analysis. Tubing lengths should be kept as short as possible, whilst striving to collect data from the furthest model extremities. Similarly, finding space for the pressure scanners is usually a challenge, so manufacturers, like Scanivalve, strive to create smaller, more space-efficient solutions. Data collection rate is also a challenge, to ensure that as many measurements as possible, often thousands per channel per second, are gathered in the available time.
To discover how Evolution Measurement solved the problem, download the full application note here Evolution_Scanivalve Motor Sport App Note