Document ID: chunk:federal_register_of_legislation:F2024L00446:reg:6600:p20
Version: federal_register_of_legislation:F2024L00446
Segment Type: reg
Provision Reference: reg 6600 (pt 20/28)
Character Range: 847692–850734

with a measurement frequency of at least 0.1 Hz;
                  (h) Vehicle mass accuracy measured on the same weighing scale before and after the test: ±10 kg (±20 kg for vehicles > 4,000 kg);
                  (i) Tyre pressure accuracy: ±5 kPa;
                  (j) Wheel rotational speed accuracy: ±0.05 s-1 or 1 per cent, whichever is greater.
              3.2. Wind tunnel criteria
              3.2.1. Wind velocity
              The wind velocity during a measurement shall remain within ±2 km/h at the centre of the test section. The possible wind velocity shall be at least 140 km/h.
              3.2.2. Air temperature
              The air temperature during a measurement shall remain within ±3 °C at the centre of the test section. The air temperature distribution at the nozzle outlet shall remain within ±3 °C.
              3.2.3. Turbulence
              For an equally-spaced 3 by 3 grid over the entire nozzle outlet, the turbulence intensity, Tu, shall not exceed 1 per cent. See Figure A4/1.
Figure A4/1
Turbulence intensity

           where:
           Tu is the turbulence intensity;
           u' is the turbulent velocity fluctuation, m/s;
           U∞ is the free flow velocity, m/s.
              3.2.4. Solid blockage ratio
              The vehicle blockage ratio  expressed as the quotient of the vehicle frontal area and the area of the nozzle outlet as calculated using the following equation, shall not exceed 0.35.
              where:
              𝜀sb is the vehicle blockage ratio;
              Af is the frontal area of the vehicle, m²;
              Anozzle is the nozzle outlet area, m².
              3.2.5. Rotating wheels
              To properly determine the aerodynamic influence of the wheels, the wheels of the test vehicle shall rotate at such a speed that the resulting vehicle velocity is within ±3 km/h of the wind velocity.
              3.2.6. Moving belt
              To simulate the fluid flow at the underbody of the test vehicle, the wind tunnel shall have a moving belt extending from the front to the rear of the vehicle. The speed of the moving belt shall be within ±3 km/h of the wind velocity.
              3.2.7. Fluid flow angle
              At nine equally distributed points over the nozzle area, the root mean square deviation of both the pitch angle α and the yaw angle β (Y-, Z-plane) at the nozzle outlet shall not exceed 1°.
              3.2.8. Air pressure
              At nine equally distributed points over the nozzle outlet area, the standard deviation of the total pressure at the nozzle outlet shall be less than or equal to 0.02.
           where:
           σ is the standard deviation of the pressure ratio;
            is the variation of total pressure between the measurement points, N/m2;
           q is the dynamic pressure, N/ m².
              The absolute difference of the pressure coefficient  over a distance 3 metres ahead and 3 metres behind the centre of the balance in the empty test section and at a height of the centre of the