An agricultural tractor is a sophisticated machine with a densely packed underhood compartment, presenting unique challenges in airflow management through its heat exchangers. The complexity of the design leads to non-uniform airflow patterns, as the fan-driven system draws air from front, top, and side openings. This variability makes it essential to establish a reliable correlation between test airflow and simulated airflow values.
Our investigation has revealed notable differences in the velocity values obtained from the Power Take-Off (PTO) test using various instrumentation. The handheld vane-type anemometer is widely utilized due to its accessibility, affordability, and simplicity. However, it is worth noting that this device can demonstrate discrepancies ranging from 70% to 90% when compared to Computational Fluid Dynamics (CFD) predictions, especially in heavy duty applications.
In this study, we have established a robust correlation between the airflow through the heat exchanger of a production tractor, as modeled in CFD, and the results obtained from the PTO test. To enhance measurement accuracy, we employed a matrix-type anemometer setup, incorporating a 3x3 grid of low resistance vane-type anemometers to cover the maximum possible area of the heat exchanger. Measurements were strategically taken behind the heat exchanger to minimize the effects of turbulence and non-uniformity, as this location typically presents a more unidirectional airflow.
Our findings clearly indicate that employing a handheld anemometer significantly narrows the discrepancy between CFD predictions and PTO test results reducing it from 70% to an impressive 15%. Moreover, our CFD analysis reveals an approximate 25% variation between velocities measured on the front and back faces of the heat exchanger. This underscores the challenges of relying on handheld anemometers, as they cannot be positioned behind the heat exchanger where airflow is more uniform, thus contributing to the observed discrepancies.
In conclusion, measuring airflow through the heat exchanger with a Matrix type anemometer placed behind it, can improves the correlation with CFD results to 84%.