40 C.F.R. §§ 1037.530–1037.534

3 sections in range

§1037.530. Wind tunnel procedures for calculating drag area ( C d A ).

40 C.F.R. § 1037.530

This section describes an alternate method for calculating drag area, CdA, for tractors using wind tunnel testing.

(a)

You may measure drag areas consistent with published SAE procedures as described in this section using any wind tunnel recognized by the Subsonic Aerodynamic Testing Association, subject to the provisions of § 1037.525. If your wind tunnel does not meet the specifications described in this section, you may ask us to approve it as an alternate method under § 1037.525(d). All wind tunnels and wind tunnel tests must meet the specifications described in SAE J1252 (incorporated by reference, see § 1037.810), with the following exceptions and additional provisions:

(1)

The Overall Vehicle Reynolds number, Re#w, must be at least 1.0·10 6. Tests for Reynolds effects described in Section 7.1 of SAE J1252 are not required.

(2)

For full-scale wind tunnel testing, use good engineering judgment to select a trailer that is a reasonable representation of the trailer used for reference coastdown testing. For example, where your wind tunnel is not long enough to test the tractor with a standard 53 foot box van, it may be appropriate to use a shorter box van. In such a case, the correlation developed using the shorter trailer would only be valid for testing with the shorter trailer.

(3)

For reduced-scale wind tunnel testing, use a one-eighth or larger scale model of a tractor and trailer that is sufficient to simulate airflow through the radiator inlet grill and across an engine geometry that represents engines commonly used in your test vehicle.

(b)

Open-throat wind tunnels must also meet the specifications of SAE J2071 (incorporated by reference, see § 1037.810).

(c)

To determine CdA values, perform wind tunnel testing with a tractor-trailer combination using the manufacturer's tractor and a standard trailer. Use a moving/rolling floor if the facility has one. For Phase 1 tractors, conduct the wind tunnel tests at a zero yaw angle. For Phase 2 and later vehicles, conduct the wind tunnel tests by measuring the drag area at yaw angles of +4.5° and −4.5° and calculating the average of those two values.

(d)

In your request to use wind tunnel testing, describe how you meet all the specifications that apply under this section, using terminology consistent with SAE J1594 (incorporated by reference, see § 1037.810). If you request our approval to use wind tunnel testing even though you do not meet all the specifications of this section, describe how your method nevertheless qualifies as an alternate method under § 1037.525(d) and include all the following information:

(1)

Identify the name and location of the test facility for your wind tunnel method.

(2)

Background and history of the wind tunnel.

(3)

The wind tunnel's layout (with diagram), type, and construction (structural and material).

(4)

The wind tunnel's design details— the type and material for corner turning vanes, air settling specification, mesh screen specification, air straightening method, tunnel volume, surface area, average duct area, and circuit length.

(5)

Specifications related to the wind tunnel's flow quality— temperature control and uniformity, airflow quality, minimum airflow velocity, flow uniformity, angularity and stability, static pressure variation, turbulence intensity, airflow acceleration and deceleration times, test duration flow quality, and overall airflow quality achievement.

(6)

Test/working section information— test section type (e.g., open, closed, adaptive wall) and shape (e.g., circular, square, oval), length, contraction ratio, maximum air velocity, maximum dynamic pressure, nozzle width and height, plenum dimensions and net volume, maximum allowed model scale, maximum model height above road, strut movement rate (if applicable), model support, primary boundary layer slot, boundary layer elimination method, and photos and diagrams of the test section.

(7)

Fan section description— fan type, diameter, power, maximum angular speed, maximum speed, support type, mechanical drive, and sectional total weight.

(8)

Data acquisition and control (where applicable)— acquisition type, motor control, tunnel control, model balance, model pressure measurement, wheel drag balances, wing/body panel balances, and model exhaust simulation.

(9)

Moving ground plane or rolling road (if applicable)— construction and material, yaw table and range, moving ground length and width, belt type, maximum belt speed, belt suction mechanism, platen instrumentation, temperature control, and steering.

(10)

Facility correction factors and purpose.

Notes, amendments, and revision history

Amendments

[81 FR 74048, Oct. 25, 2016, as amended at 86 FR 34476, June 29, 2021; 89 FR 29784, Apr. 22, 2024]

Authority

Authority: 42 U.S.C. 7401—7671q.

Source

Source: 81 FR 74048, Oct. 25, 2016, unless otherwise noted.

Amendments

[81 FR 74048, Oct. 25, 2016, as amended at 86 FR 34476, June 29, 2021; 89 FR 29784, Apr. 22, 2024]

§1037.532. Using computational fluid dynamics for calculating drag area ( C dA ).

40 C.F.R. § 1037.532

This section describes an alternate method for calculating drag area, CdA, for tractors using commercially available computational fluid dynamics (CFD) software.

(a)

For Phase 2 and later vehicles, use SAE J2966 (incorporated by reference, see § 1037.810), with the following clarifications and exceptions:

(1)

Vehicles are subject to the requirement to meet standards based on the average of testing at yaw angles of +4.5° and −4.5°; however, you may submit your application for certification with CFD results based on only one of those yaw angles.

(2)

For CFD code with a Navier-Stokes based solver, follow the additional steps in paragraph (d) of this section. For Lattice-Boltzmann based CFD code, follow the additional steps in paragraph (e) of this section.

(3)

Simulate a Reynolds number of 5.1 million (based on a 102-inch trailer width) and an air speed of 65 mi/hr.

(4)

Perform an open-road simulation (not the Wind Tunnel Simulation).

(5)

Use a free stream turbulence intensity of 0.0%.

(6)

Choose time steps that can accurately resolve intrinsic flow instabilities, consistent with good engineering judgment.

(7)

The result must be drag area (CdA), not drag coefficient (Cd), based on an air speed of 65 mi/hr.

(8)

Submit information as described in paragraph (g) of this section.

(b)

For Phase 1 tractors, apply the procedures as specified in paragraphs (c) through (f) of this section. Paragraphs (c) through (f) apply for Phase 2 and later vehicles only as specified in paragraph (a) of this section.

(c)

To determine CdA values, perform CFD modeling based on a tractor-trailer combination using the manufacturer's tractor and a standard trailer. Perform all CFD modeling as follows:

(1)

Specify a blockage ratio at or below 0.2% to simulate open-road conditions.

(2)

Assume zero yaw angle.

(3)

Model the tractor with an open grill and representative back pressures based on available data describing the tractor's pressure characteristics.

(4)

Enable the turbulence model and mesh deformation.

(5)

Model tires and ground plane in motion to simulate a vehicle moving forward in the direction of travel.

(6)

Apply the smallest cell size to local regions on the tractor and trailer in areas of high flow gradients and smaller-geometry features (e.g., the A-pillar, mirror, visor, grille and accessories, trailer-leading edge, trailer-trailing edge, rear bogey, tires, and tractor-trailer gap).

(7)

Simulate a vehicle speed of 55 mi/hr.

(d)

Take the following steps for CFD code with a Navier-Stokes formula solver—

(1)

Perform an unstructured, time-accurate analysis using a mesh grid size with a total volume element count of at least 50 million cells of hexahedral and/or polyhedral mesh cell shape, surface elements representing the geometry consisting of no less than 6 million elements, and a near-wall cell size corresponding to a y+ value of less than 300.

(2)

Perform the analysis with a turbulence model and mesh deformation enabled (if applicable) with boundary layer resolution of ±95%. Once the results reach this resolution, demonstrate the convergence by supplying multiple, successive convergence values for the analysis. The turbulence model may use k-epsilon (k-ε), shear stress transport k-omega (SST k-ω), or other commercially accepted methods.

(e)

For Lattice-Boltzmann based CFD code, perform an unstructured, time-accurate analysis using a mesh grid size with total surface elements of at least 50 million cells using cubic volume elements and triangular and/or quadrilateral surface elements with a near-wall cell size of no greater than 6 mm on local regions of the tractor and trailer in areas of high flow gradients and smaller geometry features, with cell sizes in other areas of the mesh grid starting at twelve millimeters and increasing in size from this value as the distance from the tractor and trailer increases.

(f)

You may ask us to allow you to perform CFD analysis using parameters and criteria other than those specified in this section, consistent with good engineering judgment. In your request, you must demonstrate that you are unable to perform modeling based on the specified conditions (for example, you may have insufficient computing power, or the computations may require inordinate time), or you must demonstrate that different criteria (such as a different mesh cell shape and size) will yield better results. In your request, you must also describe your recommended alternative parameters and criteria, and describe how this approach will produce results that adequately represent a vehicle's in-use performance. We may require that you supply data demonstrating that your selected parameters and criteria will provide a sufficient level of detail to yield an accurate analysis. If you request an alternative approach because it will yield better results, we may require that you perform CFD analysis using both your recommended criteria and parameters and the criteria and parameters specified in this section to compare the resulting key aerodynamic characteristics, such as pressure profiles, drag build-up, and turbulent/laminar flow at key points around the tractor-trailer combination.

(g)

Include the following information in your request to determine CdA values using CFD:

(1)

The name of the software.

(2)

The date and version number of the software.

(3)

The name of the company producing the software and the corresponding address, phone number, and Web site.

(4)

Identify whether the software uses Navier-Stokes or Lattice-Boltzmann equations.

(5)

Describe the input values you will use to simulate the vehicle's aerodynamic performance for comparing to coastdown results.

Notes, amendments, and revision history

Amendments

[81 FR 74048, Oct. 25, 2016, as amended at 86 FR 34476, June 29, 2021; 89 FR 29785, Apr. 22, 2024]

Authority

Authority: 42 U.S.C. 7401—7671q.

Source

Source: 81 FR 74048, Oct. 25, 2016, unless otherwise noted.

Amendments

[81 FR 74048, Oct. 25, 2016, as amended at 86 FR 34476, June 29, 2021; 89 FR 29785, Apr. 22, 2024]

§1037.534. Constant-speed procedure for calculating drag area ( C d A ).

40 C.F.R. § 1037.534

This section describes an alternate method for calculating drag area, CdA, for tractors using constant-speed aerodynamic drag testing.

(a)

Test track. Select a test track that meets the specifications described in § 1037.528(c)(3).

(b)

Ambient conditions. At least two tests are required. For one of the tests, ambient conditions must remain within the specifications described in § 1037.528(c) throughout the preconditioning and measurement procedure. The other tests must also meet those specifications except for the wind conditions. The wind conditions must be such that 80 percent of the values of yaw angle, ψ air, from the 50 mi/hr and 70 mi/hr test segments are between 4° and 10° or between −4° and −10°.

(c)

Vehicle preparation. Perform testing with a tractor-trailer combination using the manufacturer's tractor and a standard trailer. Prepare the tractor-trailer combination for testing as described in § 1037.528(b). Install measurement instruments meeting the requirements of 40 CFR part 1065, subpart C, that have been calibrated as described in 40 CFR part 1065, subpart D, as follows:

(1)

Measure torque at each of the drive wheels using a hub torque meter or a rim torque meter. If testing a tractor with two drive axles, you may disconnect one of the drive axles from receiving torque from the driveshaft, in which case you would measure torque at only the wheels that receive torque from the driveshaft. Set up instruments to read engine speed for calculating angular speed at the point of the torque measurements, or install instruments for measuring the angular speed of the wheels directly.

(2)

Install instrumentation to measure vehicle speed at 10 Hz, with an accuracy and resolution of 0.1 mi/hr. Also install instrumentation for reading engine speed from the engine's onboard computer.

(3)

Mount an anemometer on the trailer as described in § 1037.528(f).

(4)

Fill the vehicle's fuel tanks so they are at maximum capacity at the start of the measurement procedure.

(5)

Measure the weight over each axle to the nearest 20 kg, with a full fuel tank, including the driver and any passengers that will be in the vehicle during the test.

(d)

Measurement procedure. The measurement sequence consists of vehicle preconditioning followed by stabilization and measurement over five consecutive constant-speed test segments with three different speed setpoints (10, 50, and 70 mi/hr). Each test segment is divided into smaller increments for data analysis.

(1)

Precondition the vehicle and zero the torque meters as follows—

(i)

If you are using rim torque meters, zero the torque meters by lifting each instrumented axle and recording torque signals for at least 30 seconds, and then drive the vehicle at 50 mi/hr for at least 30 minutes.

(ii)

If you are using any other kind of torque meter, drive the vehicle at 50 mi/hr for at least 30 minutes, and then allow the vehicle to coast down from full speed to a complete standstill while the clutch is disengaged or the transmission is in neutral, without braking. Zero the torque meters within 60 seconds after the vehicle stops moving by recording the torque signals for at least 30 seconds, and directly resume vehicle preconditioning at 50 mi/hr for at least 1.25 mi.

(iii)

You may calibrate instruments during the preconditioning drive.

(2)

Perform testing as described in paragraph (d)(3) of this section over a sequence of test segments at constant vehicle speed as follows:

(i)

(300 ±30) seconds in each direction at 10 mi/hr.

(ii)

(450 ±30) seconds in each direction at 70 mi/hr.

(iii)

(450 ±30) seconds in each direction at 50 mi/hr.

(iv)

(450 ±30) seconds in each direction at 70 mi/hr.

(v)

(450 ±30) seconds in each direction at 50 mi/hr.

(vi)

(300 ±30) seconds in each direction at 10 mi/hr.

(3)

When the vehicle preconditioning described in paragraph (d)(1) of this section is complete, stabilize the vehicle at the specified speed for at least 200 meters and start taking measurements. The test segment starts when you start taking measurements for all parameters.

(4)

During the test segment, continue to operate the vehicle at the speed setpoint, maintaining constant speed and torque within the ranges specified in paragraph (e) of this section. Drive the vehicle straight with minimal steering; do not change gears. Perform measurements as follows during the test segment:

(i)

Measure the angular speed of the driveshaft, axle, or wheel where the torque is measured, or calculate it from engine speed in conjunction with gear and axle ratios, as applicable.

(ii)

Measure vehicle speed in conjunction with time-of-day data.

(iii)

Measure ambient conditions, air speed, and air direction as described in § 1037.528(e) and (f). Correct air speed and air direction as described in paragraphs (f)(1) and (2) of this section.

(5)

You may divide a test segment into multiple passes by suspending and resuming measurements. Stabilize vehicle speed before resuming measurements for each pass as described in paragraph (d)(3) of this section. Analyze the data from multiple passes by combining them into a single sequence of measurements for each test segment.

(6)

Divide measured values into even 10 second increments. If the last increment for each test segment is less than 10 seconds, disregard measured values from that increment for all calculations under this section.

(e)

Validation criteria. Analyze measurements to confirm that the test is valid. Analyze vehicle speed and drive torque by calculating the mean speed and torque values for each successive 1 second increment, for each successive 10 second increment, and for each test segment. The test is valid if the data conform to all the following specifications:

(1)

Vehicle speed. The mean vehicle speed for the test segment must be within 1.00 mi/hr of the speed setpoint. In addition, for testing at 50 mi/hr and 70 mi/hr, all ten of the 1 second mean vehicle speeds used to calculate a corresponding 10 second mean vehicle speed must be within ±0.2 mi/hr of that 10 second mean vehicle speed. Perform the same data analysis for testing at 10 mi/hr, but apply a validation threshold of ±0.1 mi/hr.

(2)

Drive torque. All ten of the 1 second mean torque values used to calculate a corresponding 10 second mean torque value must be within ±50% of that 10 second mean torque value.

(3)

Torque drift. Torque meter drift may not exceed ±1%. Determine torque meter drift by repeating the procedure described in paragraph (d)(1) of this section after testing is complete, except that driving the vehicle is necessary only to get the vehicle up to 50 mi/hr as part of coasting to standstill.

(f)

Calculations. Analyze measured data for each time segment after time-aligning all the data. Use the following calculations to determine CdA:

(1)

Onboard air speed. Correct onboard anemometer measurements for air speed using onboard measurements and measured ambient conditions as described in § 1037.528(f), except that you must first divide the test segment into consecutive 10 second increments. Disregard data from the final increment of the test segment if it is less than 10 seconds. This analysis results in the following equation for correcting air speed measurements:

(2)

Yaw angle. Correct the onboard anemometer measurements for air direction for each test segment as follows:

(i)

Calculate arithmetic mean values for vehicle speed, v, wind speed, w, and wind direction, ϕw, over each 10 second increment for each test segment. Disregard data from the final increment of the test segment if it is less than 10 seconds.

(ii)

Calculate the theoretical air direction, ψ air,th, for each 10 second increment using the following equation:

(iii)

Perform a linear regression using paired values of ψ air,th and measured air direction, ψ air,meas, from each 10 second increment for all 50 mi/hr and 70 mi/hr test segments to determine the air-direction correction coefficients, b0 and b1, based on the following equation:

(iv)

For all 50 mi/hr and 70 mi/hr test segments, correct each measured value of air direction using the following equation:

(3)

Road load force.

(i)

Average the sum of the corrected torques, the average of the wheel speed measurements, and the vehicle speed over every 10 second increment to determine, Ttotal, fnwheel, and v.

(ii)

Calculate a mean road load force, FRL[speed], for each 10 second increment using the following equation:

(4)

Determination of drag area. Calculate a vehicle's drag area as follows:

(i)

Calculate the mean road load force from all 10 second increments from the 10 mi/hr test segments from the test that was within the wind limits specified in § 1037.528(c), FRL10,test. This value represents the mechanical drag force acting on the vehicle.

(ii)

Calculate the mean aerodynamic force for each 10 second increment, Faero[speed], from the 50 mi/hr and 70 mi/hr test segments by subtracting FRL10,test from FRL[speed].

(iii)

Average the corrected air speed and corrected yaw angle over every 10 second segment from the 50 mi/hr and 70 mi/hr test segments to determine vair and ψ air.

(iv)

Calculate CdA for each 10 second increment from the 50 mi/hr and 70 mi/hr test segments using the following equation:

(v)

Plot all CdA values from the 50 mi/hr and 70 mi/hr test segments against the corresponding values for corrected yaw angle for each 10 second increment. Create a regression based on a fourth-order polynomial regression equation of the following form:

(vi)

Determine CdAwa-alt as the average of CdA values at 4.5° and −4.5° by applying Eq. 1037.534-7 at those angles.

(g)

Documentation. Keep the following records related to the constant-speed procedure for calculating drag area:

(1)

The measurement data for calculating CdA as described in this section.

(2)

A general description and pictures of the vehicle tested.

(3)

The vehicle's maximum height and width.

(4)

The measured vehicle mass.

(5)

Mileage at the start of the first test segment and at the end of the last test segment.

(6)

The date of the test, the starting time for the first test segment, and the ending time for the last test segment.

(7)

The transmission gear used for each test segment.

(8)

The data describing how the test was valid relative to the specifications and criteria described in paragraphs (b) and (e) of this section.

(9)

A description of any unusual events, such as a vehicle passing the test vehicle, or any technical or human errors that may have affected the CdA determination without invalidating the test.

Notes, amendments, and revision history

Amendments

[81 FR 74048, Oct. 25, 2016, as amended at 86 FR 34476, June 29, 2021; 88 FR 4642, Jan. 24, 2023; 89 FR 29785, Apr. 22, 2024]

Authority

Authority: 42 U.S.C. 7401—7671q.

Source

Source: 81 FR 74048, Oct. 25, 2016, unless otherwise noted.

Amendments

[81 FR 74048, Oct. 25, 2016, as amended at 86 FR 34476, June 29, 2021; 88 FR 4642, Jan. 24, 2023; 89 FR 29785, Apr. 22, 2024]

40 C.F.R. §§ 1037.530–1037.534

§1037.530. Wind tunnel procedures for calculating drag area ( C d A ).

Amendments

Authority

Source

Amendments

§1037.532. Using computational fluid dynamics for calculating drag area ( C dA ).

Amendments

Authority

Source

Amendments

§1037.534. Constant-speed procedure for calculating drag area ( C d A ).

Amendments

Authority

Source

Amendments

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