How can you design an air intake system with uniform flow and pressure distribution?

2 How to achieve uniformity

There are several factors that can influence the uniformity of the flow and pressure at the inlet face, such as the shape, size, location, and angle of the air intake system, as well as the flight speed, altitude, and angle of attack of the aircraft. To achieve uniformity in this area, it is important to consider these factors and design the air intake system accordingly. Some common design methods include utilizing a bell-mouth shape with its smooth and gradual curvature that guides the flow towards the center of the inlet face; adding a centerbody or a spike that deflects the flow and creates a low-pressure region at the center of the inlet face; applying boundary layer control techniques such as suction, blowing, or vortex generators to modify the flow near the wall of the air intake system and prevent separation and distortion; and optimizing both the inlet area and mass flow rate to match the demand of the engine.

3 How to evaluate uniformity

To evaluate the uniformity of the flow and pressure at the inlet face, you need to measure and analyze the flow parameters, such as velocity, temperature, density, and pressure, at different locations and directions on the inlet face. For this purpose, you can use various instruments and methods, such as Pitot-static probes to measure the total and static pressure of the flow and calculate the velocity and Mach number. Additionally, thermocouples or thermistors can be used to measure the temperature of the flow and calculate the density and Reynolds number. Furthermore, pressure taps or transducers measure the static pressure of the flow to calculate the pressure coefficient and the pressure recovery factor. Lastly, flow visualization techniques such as smoke, dye, or oil can show the flow patterns and reveal any separation, shock waves, or stall.

4 How to improve uniformity

If the evaluation results show that the flow and pressure are not uniform across the inlet face, you need to identify the causes and implement corrective actions. These can include inlet distortion, which is a deviation from the ideal uniform flow and pressure caused by external factors like crosswinds, obstructions, or aircraft maneuvers. To reduce inlet distortion, you can use adaptive or variable geometry air intake systems to adjust their shape, size, and angle according to the flight conditions. Inlet bleed is another possible cause, which is a leakage of air from the air intake system to the surrounding environment through gaps or holes. You can minimize this by sealing these gaps or holes, or by using a secondary air system to recirculate the leaked air back to the air intake system. Inlet icing is another potential cause, which is a formation of ice on the surface of the air intake system due to low temperature and high humidity. To prevent this, you can use anti-icing or de-icing systems to heat the air or the surface of the air intake system, or apply a coating or material that repels water or ice.

5 How to test uniformity

Testing the performance and uniformity of the air intake system under realistic conditions is essential after its design and improvement. You can use various testing facilities and methods, such as wind tunnels, engine test cells, and flight tests. Wind tunnels are closed circuits that simulate the airflow and flight conditions around the air intake system and aircraft, allowing for the measurement of flow and pressure parameters at the inlet face. Engine test cells are enclosed chambers that mount the engine and air intake system to measure their performance and efficiency. Flight tests are the final and most reliable tests, as they involve flying the aircraft and air intake system in various scenarios. This allows for recording and analyzing data from sensors and instruments installed on the aircraft and air intake system, so as to evaluate their behavior and response.