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Many UAVs today have an S-bend inlet for the sake of stealth; however, the majority of them have a relatively gentle transition of the flow channel. This study presents an experimental investigation of the aerodynamic performance and swirl flow characteristics of a UAV inlet with double 90° bends, which is also integrated with an aircraft fuselage as well as a volute. The influences of angle of attack, sideslip angle, AIP Mach number and freestream speed are explored in detail. The influences of the deflectors installed ahead of the first 90° bend of the inlet and the baffle installed at the bottom of the volute are revealed. It is found that both the deflectors and the baffle are beneficial in enhancing the aerodynamic performance of the inlet and alleviating the intensity of the swirl flow inside the volute. [ABSTRACT FROM AUTHOR]

In this study, the influence laws of different parameters on the exclusion characteristics of hailstone and ice flake, and on the aerodynamic performance of the inlet are studied by numerical method. The motion of the hailstone and ice flake is simulated using the 6-DOF method. Results show that the inhalation of hailstone in the inlet decreases total pressure distortion by about 20%, and the total pressure recovery coefficient is essentially unchanged. Icing of the upper lip decreases the total pressure distortion of the inlet by about 22%, and the total pressure recovery coefficient decreases by 0.6%. The ice flakes on the inner and outer lip, when shed and brake by collision with the center body, will cause damage to the engine duct. The shedding and breaking of ice flake at an angle of 150° to the lip can result in a large amount of ice flake debris entering the engine duct, threatening the performance and structure of the engine in the rear. The motion characteristics of hailstone and ice flake under helicopter fuselage/rotor/inlet integration conditions are revealed. It also provides a reference on the numerical methods for the numerical study of hailstone/ice flake exclusion characteristics of helicopter fuselage/rotor/inlet integration conditions. [ABSTRACT FROM AUTHOR]

In the vertical take-off and landing (VTOL) state of tiltrotor aircraft, the inlet entrance encounters the incoming airflow at a 90° attack angle, resulting in highly complex internal flow characteristics that are extremely susceptible to gusts. Meanwhile, the flow quality at the inlet exit directly affects the performance of the aircraft's engine. This work made use of an unsteady numerical simulation method based on sliding meshes to investigate the internal flow characteristics of the inlet during the hover state of a typical tiltrotor aircraft and the effects of head-on gusts on the inlet's aerodynamic characteristics. The results show that during the hover state, the tiltrotor aircraft inlet features three pairs of transverse vortices and one streamwise vortex at the aerodynamic interface plane (AIP). The transverse vortices generated due to the rotational motion of the air have the largest scale and exert the strongest influence on the inlet's performance, which is characterized by pronounced unsteady features. Additionally, strong unsteady characteristics are present within the inlet. Head-on gusts mainly affect the mechanical energy and non-uniformity of the air sucked into the inlet by influencing the direction of the rotor's induced slipstream, thereby impacting the performance of the inlet. The larger head-on gusts have beneficial effects on the performance of the inlet. When the gust velocity reaches 12 m/s, there is a 1.01% increase in the total pressure recovery (σ) of the inlet, a 25.72% decrease in the circumferential distortion index (DC60), and a reduction of 62.84% in the area where the swirl angle |α| exceeds 15°. Conversely, when the gust velocity of head-on gusts reaches 12 m/s in the opposite direction, the inlet's total pressure recovery decreases by 1.13%, the circumferential distortion index increases by 14.57%, and the area where the swirl angle exceeds 15° increases by 69.59%, adversely affecting the performance of the inlet. Additionally, the presence of gusts alters the unsteady characteristics within the inlet. [ABSTRACT FROM AUTHOR]

In this paper, a novel flow perturbation model meant to investigate the effects of incoming wind shear on a hypersonic inlet/isolator is presented. This research focuses on the transient shock/boundary layer interaction and shock train flow evolution in a hypersonic inlet/isolator with an on-design Mach number of 6.0 under incoming wind shear at high altitudes, precisely at an altitude of 30 km with a magnitude speed of 80 m/s. Despite the low intensity of wind shear at high altitudes, the results reveal that wind shear significantly disrupts the inlet/isolator flowfield, affecting the shock wave/boundary layer interaction in the unthrottled state, which drives the separation bubble at the throat to move downstream and then upstream. Moreover, the flowfield behaves as a hysteresis phenomenon under the effect of wind shear, and the total pressure recovery coefficients at the throat and exit of the inlet/isolator increase by approximately 10% to 12%. Furthermore, this research focuses on investigating the impact of wind shear on the behavior of the shock train. Once the inlet/isolator is in a throttled state, wind shear severely impacts the motion of the shock train. When the downstream backpressure is 135 times the incoming pressure (p0), the shock train first moves upstream and gradually couples with a cowl shock wave/boundary layer interaction, resulting in a more significant separation at the throat, and then moves downstream and decouples from the separation bubble at the throat. However, if the downstream backpressure increases to 140 p0, the shock train enlarges the separation bubble, forcing the inlet/isolator to fall into the unstart state, and it cannot be restarted. These findings emphasize the need to consider wind shear effects in the design and operation of hypersonic inlet/isolator. [ABSTRACT FROM AUTHOR]

Gust is a common atmospheric turbulence phenomenon encountered by aircraft and is one major cause of several undesired instability problems. Although the response of aircraft to the incoming gust has been widely investigated within the subject of external-flow aerodynamics in the past decades, little attention is paid to its effects on the internal flow within aircraft engines. In this paper, a newly implemented Field Velocity Method (FVM) in OpenFOAM is used to simulate the flow field and aerodynamic responses of a serpentine inlet exposed to non-stationary horizontal sinusoidal gusts. Validations are performed on the results obtained based on the baseline Computational Fluid Dynamics (CFD) solver and the gust modeling method. Finally, the flow field and aerodynamic characteristics of the serpentine inlet under horizontal sinusoidal gust conditions are comprehensively investigated. It is found that the gusts not only significantly change the flow structure but also play an unfavorable role in the total pressure distortion of the serpentine inlet. This finding shows the necessity to consider gust effects when designing and evaluating the performance of aircraft engines. [ABSTRACT FROM AUTHOR]

Turboprop aircraft plays an important role in the field of regional airliners and military transport. During take-off or landing, turboprop aircrafts frequently encounter bird flocks that can be ingested into the engine inlet, thereby posing a significant threat to flight safety. Consequently, the aerodynamic characteristics and bird ingestion characteristics of turboprop inlet are investigated in this article. An unsteady computational fluid dynamics (CFD) approach has been proposed to calculate bird ingestion characteristics in a turboprop inlet with different bulge heights under propeller interference by combining a self-developed collision-rebound model with the overset mesh method and 6-degree of freedom (6-DOF) motion method. Considering the characteristics of bird strikes, a parameterized controlled bulge of turboprop inlet with a scavenge duct has been designed. Moreover, the trajectory characteristics of the bird, bird-inlet coupling flowfield characteristics and the aerodynamic characteristics are analyzed in depth. The bulge of the inlet plays a positive role in preventing the bird object from entering the engine duct at a 23° incidence angle. The bird rebounds from the upper bulge and is discharged through the scavenge duct at Ma AIP =0.45. The results show that the growth of inlet bulge height has the minimal influence on the total pressure recovery coefficient σ, with only approximately 0.3% variation within the bulge height range of interest. However, it significantly affects the total pressure distortion DC60 with an increase up to 84%. [ABSTRACT FROM AUTHOR]

The flow response hysteresis in a mixed-compression supersonic inlet's throttling/unthrottling process is unconducive to its practical engineering applications. To suppress such hysteresis, herein, a flow control method based on a distributed bleed system in the inlet's internal contraction part was proposed and applied to a rectangular supersonic inlet with a designed Mach number of 4.0 and an internal contraction ratio of 1.5. All tests were conducted in a supersonic wind tunnel at a freestream Mach number of 2.9, and the relevant test data were obtained using the high-speed schlieren and dynamic pressure measurement systems. The results indicate that the distributed bleed system improved the uncontrolled inlet's unstart throttling ratio from 43.8% to 47.3% and the restart throttling ratio from 29.4% to 47.1%, and it essentially eliminated the flow response hysteresis during the throttling/unthrottling process. Moreover, the hysteresis mechanism of the uncontrolled inlet, dominated by the separation-induced flow structures in the internal contraction part, was investigated to help elucidate the targeted control mechanism of the bleed system that suppresses the hysteresis. Finally, the specific flow phenomena in the oscillation of the controlled inlet were examined to study the bleed system's impact on the unsteady flowfield, including the coupled flow of the mainstream with the bleed system and complex wave motion structures. • Flow response hysteresis in a mixed-compression supersonic inlet's downstream throttling/unthrottling process is experimentally investigated. • An effective hysteresis suppression method based on a distributed bleed system is proposed. • New flow phenomena in the oscillation of the inlet under bleed control were examined. [ABSTRACT FROM AUTHOR]