Total Air Temperature Probe Flow Separation Trip
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Solution Overview
Problem
Conventional total air temperature (TAT) probes face challenges in icing conditions and boundary layer separation, leading to errors in air temperature measurement due to ice accumulation and deicing heater errors (DHE), which are difficult to correct.
Innovation Solution
A total air temperature probe design featuring a strut with a sensor passage angled relative to the airflow, a deicing heater to form a heated boundary layer, and a flow separation trip feature positioned to avoid the sensor, along with an optional thermal shield, reduces deicing heater error by preventing heated boundary layer contact with the sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If deicing heaters are used to prevent ice formation on the probe, then ice protection is improved, but deicing heater error (DHE) increases due to heated boundary layer contact with the sensor
Solution Approach 1:
The probe is divided into functionally distinct zones: a heated zone for ice protection and a separate sensing zone for accurate measurement. The sensor is positioned in a region isolated from the heated boundary layer, while heaters are applied to specific surfaces (elbow exterior, probe mount) that do not directly contact the sensor location, achieving both ice protection and measurement accuracy through spatial segmentation.
Solution Approach 2:
A thermal shield or cold wall structure acts as an intermediary barrier between the heated boundary layer and the temperature sensor. This intermediate element protects the sensor from direct thermal contact with the heated airflow, allowing the heaters to function for ice protection while preventing DHE from affecting measurements.
2Measurement precision
If bleed holes are used to control the boundary layer, then boundary layer control is improved, but flow stagnation occurs at high velocities causing DHE
Solution Approach 1:
The design extracts or eliminates the bleed hole system entirely, replacing it with alternative boundary layer control methods such as strategically positioned heaters and thermal shields. This removes the stagnation problem inherent in bleed hole systems at high velocities while maintaining boundary layer control through other means.
Solution Approach 2:
The approach changes the operational parameters from active bleed hole flow control to passive thermal management using heaters and shields. By changing from a flow-removal mechanism to a thermal-isolation mechanism, the system avoids stagnation issues while maintaining measurement accuracy across different flight conditions.
3Measurement precision
If the sensor is positioned in the main airflow path, then TAT measurement is improved, but ice accumulation on the sensor increases
Solution Approach 1:
Heated surfaces such as the elbow exterior and probe mount act as intermediary elements that prevent ice accumulation in the airflow path. These intermediate heated structures create a protective thermal environment that stops ice particles from reaching and accumulating on the sensor, while the sensor remains positioned in the main airflow for accurate measurements.
Solution Approach 2:
Heaters are positioned to preemptively heat the airflow and surrounding surfaces before ice particles can reach the sensor. This preliminary heating action prevents ice accumulation from occurring in the first place, allowing the sensor to remain exposed to the main airflow without contamination risk.
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 design reduces or eliminates deicing heater error, providing more consistent and accurate TAT measurements, especially at high altitudes, and minimizes sensitivity to boundary layer separation, thereby improving probe performance and reducing miscomparisons between multiple probes.
Implementation Method 1
A deicing heater is operatively connected to heat the probe head and to form a heated boundary layer within the primary flow passage
Implementation Method 2
A flow separation trip feature is defined on an interior surface of the probe head for tripping a boundary layer flow separation in flow in the primary flow passage
Data Source
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AI summary
A total air temperature probe (100) includes a probe head (102) having an airflow inlet (110), a main airflow outlet (112), a main probe head wall (108) and a flow separation bend wall (118). The flow separation bend wall (118) is opposite the main probe head wall (108) across a primary flow passage (120). A flow separation trip feature (122; 222) is defined on an interior surface of the main probe head wall (108) for tripping a boundary layer flow separation in flow in the primary flow passage (120), e.g., for reduction of deicing heater error.