Ground Vehicle Air Data System Using Static Pressure Reference Tank
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Solution Overview
Problem
Conventional methods for determining the drag coefficient and pressure coefficients of truck/trailer combinations are inaccurate due to the placement of static pressure probes within disturbed airflow, leading to measurement biases and errors in freestream static pressure readings.
Innovation Solution
An air measurement system that includes an insulated air tank connected to the outside atmosphere, allowing for accurate static pressure reference, a total pressure probe to measure airflow, and differential pressure probes to calculate dynamic pressure, enabling precise determination of drag and pressure coefficients by isolating the static pressure from the vehicle's influence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the static pressure probe is placed close to the vehicle to keep the measurement system compact, then the device complexity is reduced, but the measurement precision deteriorates due to exposure to disturbed airflow
Solution Approach 1:
The air tank captures and stores the freestream static pressure before the vehicle motion disturbs the airflow. By performing the pressure capture action in advance (when the vehicle is stationary or at low speed), the system preserves the accurate freestream pressure reference without needing to place the probe in undisturbed airflow during high-speed operation.
Solution Approach 2:
The air tank acts as an intermediary medium that decouples the static pressure measurement from the disturbed airflow environment. Instead of directly measuring static pressure in the fluctuating airflow near the vehicle, the system uses the air tank to transfer and preserve the freestream pressure reference, eliminating the harmful influence of flow disturbances on the measurement.
2Measurement precision
If the static pressure probe is placed far from the vehicle into the freestream to improve measurement accuracy, then the measurement precision improves, but the device complexity and cost increase due to very long probes
Solution Approach 1:
The system performs the static pressure capture action in advance during low-speed or stationary conditions when freestream pressure is easily accessible. The air tank stores this pre-captured pressure reference, eliminating the need for long probes that would be required to reach undisturbed airflow during high-speed operation.
Solution Approach 2:
The air tank creates a copy of the freestream static pressure condition and stores it for later use during vehicle operation. This pressure copy serves as a reference that can be used to calculate dynamic pressure and drag coefficient without requiring continuous access to the actual freestream environment, thereby eliminating the need for long probes.
3Device complexity
If conventional static pressure probes are used in disturbed airflow, then the measurement system remains simple, but the measurement precision deteriorates due to bias errors from location-dependent readings
Solution Approach 1:
The system captures the accurate freestream static pressure in advance before vehicle motion creates flow disturbances. By performing the pressure measurement action preliminarily (when the vehicle is stationary or at rest), the air tank stores a reference pressure that is free from location-dependent bias errors that would occur during vehicle operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method provides accurate and cost-effective determination of drag and pressure coefficients by using the air tank's static pressure as a reference, reducing measurement inaccuracies and bias errors, and allowing for precise calculations of drag and pressure coefficients.
Implementation Method 1
an air tank configured to be carried by a vehicle; a valve connecting the air tank with outside atmosphere
Implementation Method 2
measuring a total pressure with a total pressure probe carried by the vehicle
Implementation Method 3
determining a dynamic pressure as a differential pressure between a first pressure measured by the total pressure probe and a second pressure in the air tank
Implementation Method 4
the air tank includes thermal insulation
Data Source
AI summary
Ground vehicle air data systems, and associated methods are disclosed herein. In one embodiment, a method for determining a drag coefficient of a vehicle includes the steps of: while the vehicle is at rest, opening a valve that connects an air tank with an outside atmosphere; while the vehicle is at rest, closing the valve that connects the air tank with the outside atmosphere; and while the vehicle is in motion, measuring a total pressure with a total pressure probe carried by the vehicle.