Imagine you’re a fighter pilot, heading into enemy territory undetected, thanks to the stealth technology of your aircraft. But how exactly does this technology work?
Well, to achieve a minimal radar and thermal signature, the turbojet engine of the aircraft must be hidden deep within the fuselage. In order to provide the engine with the necessary air flow, small rectangular inlets are connected to the wings using Serpentine ducts, which are essentially double-S-shaped tubes.
However, this configuration poses a challenge for the engine, as it requires a large volume of high total pressure air flow at the Aerodynamic Interface Plane, or AIP. As the air flows through the S-bend of the duct, it tends to separate from the walls, creating huge swirls of low total pressure air that flow into the engine. This can cause a significant loss of total pressure and efficiency.
To mitigate this problem, engineers must focus on controlling the secondary boundary layer flow and swirl vortex creation upstream of the AIP. By reducing the intensity of these vortices, the total pressure loss at the AIP can be minimized, allowing for more efficient engine operation and greater stealth capability.
Now imagine revolutionizing the stealth technology of an aircraft through the power of active flow control. Thanks to our experimental test rig, which combined a wind-tunnel and full-scale fiberglass serpentine duct, we did just that.
To achieve the best possible results, we analysed the most cutting-edge methods of flow control and ultimately chose Vortex-Generator Jets (VGJs) over passive control methods. These VGJs are installed on the duct wall at an angle to the flow direction, creating mixing in the boundary layer and reducing the intensity of swirl vortex roll-up, leading to a reduction in total pressure loss.
But it wasn’t easy. We tested countless design parameters, including the number of jet rows, angular separation of jets, velocity ratio of jet to duct flow velocity, pitch and yaw angles of the jets, and more. But in the end, we arrived at the perfect set-up, resulting in the optimal reduction of swirl and total pressure loss.
Key Measurements/Instrumentation:
Our team worked tirelessly to test various design parameters. And the results were fascinating: a 20% reduction in total pressure loss with the best configuration we could achieve.
But that is not all. Our preliminary tests showed that pulsed VGJs offer even greater potential for improvement. The advantages of Vortex-Generator Jets as a low-drag option for reducing boundary layer separation cannot be denied.
Through our work, we opened the door to a new era of stealth technology with potential to revolutionize the way we think about flow control.
