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24 pages, 1779 KiB

Open AccessArticle

A Time-Domain Calculation Method for Gust Aerodynamics in Flight Simulation

by Zexuan Yang, Chao Yang, Daxin Wen, Wenbo Zhou and Zhigang Wu

Aerospace 2024, 11(7), 583; https://doi.org/10.3390/aerospace11070583 - 16 Jul 2024

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Abstract

Gusts have a significant impact on aircraft and need to be analyzed through flight simulations. The solution for time-domain gust aerodynamic forces stands as a pivotal stage in this process. With the increasing demand for flight simulations within gusty environments, traditional methods related [...] Read more.

Gusts have a significant impact on aircraft and need to be analyzed through flight simulations. The solution for time-domain gust aerodynamic forces stands as a pivotal stage in this process. With the increasing demand for flight simulations within gusty environments, traditional methods related to gust aerodynamics cannot fail to balance computational accuracy and efficiency. A method that can be used to quickly and accurately calculate the time-domain gust aerodynamic force is needed. This study proposes the fitting strip method, a gust aerodynamic force solution method that is suitable for real-time flight simulations. It only requires the current and previous gust information to calculate the aerodynamic force and is suitable for different configurations of aircraft and different kinds of gusts. Firstly, the fitting strip method requires the division of fitting strips and the calculation of the aerodynamic force under calibration conditions. In this study, the double-lattice method and computational fluid dynamics are used to calculate the aerodynamic force of the strips. Then, the amplitude coefficients and time-delay coefficients are obtained through a fitting calculation. Finally, the coefficients and gust information are put into the formula to calculate the gust aerodynamic force. An example of a swept wing is used for validation, demonstrating congruence between the computational results and experimental data across subsonic and transonic speeds, which proves the accuracy of the fitting strip method in both discrete gusts and continuous gusts. Compared with other methods, the fitting strip method uses the shortest time. Furthermore, the results of a calculation for normal-layout aircraft show that this method avoids the shortcomings of the rational function approximation method and is more accurate than the gust grouping method. Concurrently, gust aerodynamic force calculations were performed on aircraft with large aspect ratios and used in a real-time flight simulation. Full article

(This article belongs to the Special Issue Gust Influences on Aerospace)

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23 pages, 21901 KiB

Open AccessArticle

Numerical Study on Rotor–Building Coupled Flow Field and Its Influence on Rotor Aerodynamic Performance under an Atmospheric Boundary Layer

by Yang Liu, Yongjie Shi, Aqib Aziz and Guohua Xu

Aerospace 2024, 11(7), 521; https://doi.org/10.3390/aerospace11070521 - 27 Jun 2024

Viewed by 387

Abstract

In urban settings, buildings create complex turbulent conditions, affecting helicopter flight performance during missions and increasing safety risks during takeoff and landing. A numerical study on rotor–building coupled flow field is carried out to address rotor aerodynamic performance under building interferences in natural [...] Read more.

In urban settings, buildings create complex turbulent conditions, affecting helicopter flight performance during missions and increasing safety risks during takeoff and landing. A numerical study on rotor–building coupled flow field is carried out to address rotor aerodynamic performance under building interferences in natural atmospheric conditions. A high-fidelity atmospheric boundary layer (ABL) model described by an exponential law is established herein. The solution of the coupled flow field is based on the Reynolds-averaged Navier–Stokes (RANS) equations, with the rotor’s rotation achieved through the overset grid method. Based on the dominant wind features, the building flow field is distributed into four regions, where the updraft along the headwind side impacts the rotor, bringing about a 76% increase in pitching moment. On the lateral side of the building, distorted rotor wake squeezed upward into the rotor disk, leading to severe blade–vortex interaction (BVI). During low-altitude hovering over rooftops, the mixing of building shed vortices with forward flow wakes causes the formation of a circulation region on the rotor’s windward side, resulting in a thrust loss of approximately 7.8%. Meanwhile, the flow environment on the leeward side of the buildings is more stable. Therefore, it is recommended that helicopters adopt a headwind approach during rooftop operations. However, an 11.4% loss in the average hover figure of merit is observed due to consistent thrust losses caused by the recirculation region. Full article

(This article belongs to the Special Issue Gust Influences on Aerospace)

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16 pages, 2702 KiB

Open AccessArticle

Experimental Validation of a Passive-Adaptive Slat Concept and Characterization under Sinusoidal Fluctuations in the Angle of Attack

by Piyush Singh, Florian Schmidt, Jochen Wild, Johannes Riemenschneider, Joachim Peinke and Michael Hölling

Aerospace 2024, 11(5), 353; https://doi.org/10.3390/aerospace11050353 - 29 Apr 2024

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Abstract

This article presents an experimental investigation of a passive-adaptive slat concept, an aerodynamic control mechanism aimed at avoiding separation in the inwards region of a horizontal axis wind turbine blade. The passive-adaptive slat is designed to autonomously adjust its position due to the [...] Read more.

This article presents an experimental investigation of a passive-adaptive slat concept, an aerodynamic control mechanism aimed at avoiding separation in the inwards region of a horizontal axis wind turbine blade. The passive-adaptive slat is designed to autonomously adjust its position due to the aerodynamic forces acting on it, without the need of any active control system or external power source. The slat opens when the angle of attack increases beyond a certain threshold so that stall is delayed and closes for smaller angles of attack to increase the lift-to-drag ratio of the airfoil. A thorough aerodynamic characterisation of the passive-adaptive slat is performed in the wind tunnel followed by testing it under different sinusoidal inflows generated by a 2D active grid. It is observed that the slat system is able to leverage the advantages of both a clean airfoil and an airfoil with a fixed slat. It has the capability of delaying stalls for higher angles of attack, as well as having higher lift-to-drag ratio for lower angles of attack. It is also observed that, for fluctuating inflow, the passive-adaptive slat is able to achieve similar mean lift values as an airfoil with fixed slat while showing significant reduction in the lift fluctuations. Full article

(This article belongs to the Special Issue Gust Influences on Aerospace)

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20 pages, 19914 KiB

Open AccessArticle

Investigation of the Internal Flow Characteristics of a Tiltrotor Aircraft Engine Inlet in a Gust Environment

by Haicheng Zhu, Xiaoming He, Yue Zhang, Daishu Cheng, Ziyun Wang, Yufeng Huang and Huijun Tan

Aerospace 2024, 11(5), 342; https://doi.org/10.3390/aerospace11050342 - 25 Apr 2024

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Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Gust Influences on Aerospace)

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18 pages, 8358 KiB

Open AccessArticle

Wind Tunnel Investigation of Transient Propeller Loads for Non-Axial Inflow Conditions

by Catharina Moreira, Nikolai Herzog and Christian Breitsamter

Aerospace 2024, 11(4), 274; https://doi.org/10.3390/aerospace11040274 - 30 Mar 2024

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Abstract

Recent developments in electrical Vertical Take-off and Landing (eVTOL) vehicles show the need for a better understanding of transient aero-mechanical propeller loads for non-axial inflow conditions. The variety of vehicle configurations conceptualized with different propellers in terms of blade geometry, number of blades, [...] Read more.

Recent developments in electrical Vertical Take-off and Landing (eVTOL) vehicles show the need for a better understanding of transient aero-mechanical propeller loads for non-axial inflow conditions. The variety of vehicle configurations conceptualized with different propellers in terms of blade geometry, number of blades, and their general integration concept results in aerodynamic loads on the propellers which are different from those on conventional fixed-wing aircraft propellers or helicopter rotors. Such varying aerodynamic loads have to be considered in the vehicle design as a whole and also in the detailed design of their respective electric propulsion systems. Therefore, an experimental approach is conducted on two different propeller blade geometries and a varying number of blades with the objective to explore the characteristics at non-axial inflow conditions. Experimental data are compared with calculated results of a low-fidelity Blade Element Momentum Theory (BEMT) approach. Average thrust and side force coefficients are shown to increase with inflow angle, and this trend is captured by the implemented numerical method. Measured thrust and in-plane forces are shown to oscillate at the blade passing frequency and its harmonics, with higher amplitudes at higher angles of inflow or lower number of blades. Full article

(This article belongs to the Special Issue Gust Influences on Aerospace)

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19 pages, 6507 KiB

Open AccessArticle

Development of a Novel Small-Scale Gust Generator Research Facility

by Zhenlong Wu, Tianyu Zhang, Yuan Gao and Huijun Tan

Aerospace 2024, 11(1), 95; https://doi.org/10.3390/aerospace11010095 - 19 Jan 2024

Viewed by 1123

Abstract

In this paper, a novel small-scale gust generator research facility was designed and examined for generating Sears-type gusts. The design scheme, integration with the wind tunnel, experiment and validation of its capability are presented in detail. To help design the gust generator and [...] Read more.

In this paper, a novel small-scale gust generator research facility was designed and examined for generating Sears-type gusts. The design scheme, integration with the wind tunnel, experiment and validation of its capability are presented in detail. To help design the gust generator and validate the experimental results of the flow field characteristics generated by the developed gust generator, two numerical simulation methods, the field velocity method (FVM) and oscillating vane method (OVM), were utilized to detect the impacts of the geometrical parameters of the oscillating vanes and the downstream test model. The filtered experimental measurement results agree well with the numerical data, validating the capability of the developed gust generator to produce sinusoidal gusts. However, it should be noted that necessary measures are needed to prevent mechanical noise from interfering with the gusty flow field, which will be a focus of future research. Full article

(This article belongs to the Special Issue Gust Influences on Aerospace)

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22 pages, 11257 KiB

Open AccessArticle

Suction Control of a Boundary Layer Ingestion Inlet

by Lei Liu, Guozhan Li, Ban Wang and Shaofeng Wu

Aerospace 2023, 10(12), 989; https://doi.org/10.3390/aerospace10120989 - 24 Nov 2023

Viewed by 1351

Abstract

This study presents a numerical investigation of suction control in an aggressive S-shaped air intake with large boundary ingestion. The results show that the variation of suction control parameters such as suction location, suction pipe diameter, and suction angle all have an impact [...] Read more.

This study presents a numerical investigation of suction control in an aggressive S-shaped air intake with large boundary ingestion. The results show that the variation of suction control parameters such as suction location, suction pipe diameter, and suction angle all have an impact on the effectiveness of the flow control. In general, further upstream suction, such as near the throat, is favorable for the decrease of the second flow intensity and the area of the low-energy fluid region at the exit of the S-shaped inlet. However, it is bad for the total pressure recovery and the circumferential total pressure uniform distribution. From the perspective of the uniformity of the total pressure distribution at the air intake exit, there is an optimal location for suction between the throat and the separation start point. A bigger suction pipe diameter brings better effects as the suction location and suction angle keep constant, due to more low-energy fluid being sucked out. But this doesn’t mean the largest mass flow suction results in the biggest improvement. Overall, sucking at the 1st bend, with suction angle and suction pipe diameter equaling 15 degrees and 12 mm, respectively, is the optimal suction scheme here. Since the change rule of the cross-section area along the centerline has not changed during suction control, the second flow and complex surface streamline at the air intake exit cannot be eliminated, though they can be decreased a lot with reasonable suction control. Similarly, owing to large boundary ingestion, the remarkable low-energy fluid region always exists despite the significant reduction of the separation and second flow, which is very different from the results of this kind of micro-suction executed in the non-BLI S-duct. To pursue a higher improvement, suction combined with vortex generator vanes has been further studied. Corresponding results analysis shows that the hybrid flow control method has great potential and should be investigated in detail in the future. Full article

(This article belongs to the Special Issue Gust Influences on Aerospace)

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Review

Jump to: Research

13 pages, 2662 KiB

Open AccessReview

A Mini-Review of Recent Developments in Plenoptic Background-Oriented Schlieren Technology for Flow Dynamics Measurement

by Yulan Liu, Feng Xing, Liwei Su, Huijun Tan and Depeng Wang

Aerospace 2024, 11(4), 303; https://doi.org/10.3390/aerospace11040303 - 12 Apr 2024

Viewed by 994

Abstract

To uncover the underlying fluid mechanisms, it is crucial to explore imaging techniques for high-resolution and large-scale three-dimensional (3D) measurements of the flow field. Plenoptic background-oriented schlieren (Plenoptic BOS), an emerging volumetric method in recent years, has demonstrated being able to resolve volumetric [...] Read more.

To uncover the underlying fluid mechanisms, it is crucial to explore imaging techniques for high-resolution and large-scale three-dimensional (3D) measurements of the flow field. Plenoptic background-oriented schlieren (Plenoptic BOS), an emerging volumetric method in recent years, has demonstrated being able to resolve volumetric flow dynamics with a single plenoptic camera. The focus-stack-based plenoptic BOS system can qualitatively infer the position of the density gradient in 3D space based on the relative sharpness of the refocused BOS image. Plenoptic BOS systems based on tomography or specular enhancement techniques are realized for use in high-fidelity 3D flow measurements due to the increased number of acquisition views. Here, we first review the fundamentals of plenoptic BOS, and then discuss the system configuration and typical application of single-view and multi-view plenoptic BOS. We also discuss the related challenges and outlook on the potential development of plenoptic BOS in the future. Full article

(This article belongs to the Special Issue Gust Influences on Aerospace)

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