Aerodynamic Loads Research Articles

Flow characteristics induced by a multiform windbreak in complex terrains with and without a train: A simplified method for calculating aerodynamic loads

This study aims to investigate common multiform windbreaks, aligned parallel to railway tracks and perpendicular to incoming wind, in complex terrains. Using unsteady simulations, the study analyzes airflow downstream of these windbreaks and the aerodynamic characteristics during train passage. It evaluates the wind-protection performance of various windbreak types and transitions and identifies factors that influence performance. Results indicate that the vertical surface walls offer stronger wind protection compared to slope walls or viaduct barriers. Flow patterns near transitions reveal that upstream airflow shifts longitudinally from high-performance windbreaks to lower-performance ones, reentering the railway line space from the latter. This suggests a design approach in which neighboring windbreaks exhibit similar performance to optimize protection. On aerodynamic characteristics of the train, the maximum side force on the leading vehicle is found proportional to wind speed and train speed to the powers of 1.6 and 0.5, respectively; train speed affects the pressure on the streamlined head and the vortices around the leeward side. A simplified calculation for aerodynamic loads on a vehicle is proposed and explored with a consideration of wind speed above the railway line. An error margin of the maximum side force by this simplified method is 8.4%, and the saving is at least 88.2% of the computational resources when assessing the crosswind stability of a vehicle. The proposed design for the multiform windbreak, along with the simplified calculation method, can improve the performance of a multiform windbreak and increase the efficiency of assessing crosswind safety for railway operations downstream of the windbreak.

Study on combined thermal protection scheme integrating supercritical CO2 regenerative cooling and fuel film cooling used for scramjet engines

Supercritical CO2 closed-Brayton-cycle demonstrates considerable application potential on hypersonic vehicles, effectively addressing power supply issues during prolonged flights. However, the CO2 flow rate is strictly limited by the cycle’s cooling source (aviation kerosene), rendering traditional regenerative cooling inadequate for sufficiently cooling the scramjet engine. To address this challenge, this study proposes an integrated cooling scheme that combines regenerative cooling, ceramic thermal-protective layer, and fuel film cooling. A two-dimensional coupled numerical model was developed, simultaneously considering the convective heat transfer of supercritical CO2 and the shear mixing of supersonic fuel film. The results indicate that the high-enthalpy gas imposes an extreme aerodynamic heat load on the regenerative cooling channel wall, resulting in a notable deterioration in heat transfer for supercritical CO2. Implementing kerosene film cooling within the combustor can effectively mitigate the abnormal heat transfer behavior of supercritical CO2 and significantly reduce viscous dissipation heat within the gas boundary layer. By optimizing the fuel film injection layout, this combined cooling scheme reduced wall heat flux by 43% and temperature by over 400 K compared to traditional regenerative cooling, thus providing effective thermal protection for the scramjet engine.

Study on flexural resilience of composite foam sandwich structures under hygrothermal environment

Under hygrothermal environments, the structural stability and strength of all-fiber composite aircraft are significantly affected during long-term flight use. The wing skin, as a critical structural component, plays a vital role in bearing and transmitting aerodynamic loads. Therefore, it is crucial to investigate the structural compressive stability and strength of the wing skin throughout the aircraft's entire life cycle under these conditions. This study employs a real wing carbon fiber foam sandwich structure to investigate the compressive stability and strength of the wing skin structure of a new energy aircraft under actual flight conditions, specifically during the entire process of the room temperature dry state (RTD) and elevated temperature wet state (ETW). Initially, three-point bending tests were conducted on carbon fiber reinforced polymer (CFRP) laminates, foam cores, and CFRP reinforced foam sandwich structures. The CFRP laminates fully rebounded after bending damage in both the RTD and ETW environments. While CFRP reinforced foam sandwich structures also rebounded fully in the RTD environment, their rebound performance diminished in hygrothermal conditions due to the thermoplastic mobility of the foam cores, resulting in only weak rebound capabilities. In hygrothermal environments, the thermoplastic mobility of the foam core leads to diminished resilience after bending damage, resulting in only weak rebound capabilities. Subsequently, compressive instability tests were conducted on the wing skin foam sandwich structure. The results indicated that the basic test study effectively predicted the structural test outcomes. Structural components in the RTD environment exhibited overall flexural instability under compressive load, with damage morphology resembling a circular curve; the damaged specimens fully rebounded after unloading. Conversely, specimens in the ETW environment displayed localized instability, characterized by a wrinkled damage profile, resulting in only weak rebound capabilities after unloading.

Assessment of typhoon-induced wind and wave effects on fatigue crack growth life in offshore wind turbines

ABSTRACT Fatigue and structural failures in OWT towers are common due to sustained aerodynamic and wave loads. This study predicts the remaining service life of 2.1MW jacket-type Offshore Wind Turbine (OWT) towers, focusing on fatigue crack growth life (FCGL). Using one-way fluid-structure interaction (FSI) simulations with Typhoon "Muifa" parameters, it analyzes stress under wind, wave, and current effects. FNK theory and linear elastic fracture mechanics are applied to calculate FCGL under various loads. The results indicate that the participation of waves and currents significantly affects the stress distribution in both the tower and the tower frame. During the crack propagation process, cracks initially propagate along the thickness direction and then extend along a straight path after penetrating the thickness. Under typhoon conditions, waves and currents cause a significant reduction in the FCGL of the tower, decreasing from 2.46 years to 1.48 years numerically.

Abrupt changing aerodynamic loads resulting in diminished ride comfort when two high-speed trains intersect in a tunnel

The lateral force exerted when two trains pass each other can adversely affect train safety, and this adverse effect becomes more pronounced as the train speed increases. When trains cross paths in tunnels, the aerodynamics differ from those in open lines due to the restrictive nature of tunnel walls. Utilizing the Renormalization Group (RNG) k-ε turbulence model and the “Mosaic” grid method, this research examines changes in aerodynamic load of the train and ride comfort during a intersection at 400 km/h in a tunnel and contrasts this with conditions at 350 km/h. The results indicate that the change in aerodynamic load on each carriage is more pronounced when the head train of the oncoming train passes than when its tail train passes, with the largest variation observed during the passing of both the head and tail trains. This alteration in aerodynamic load is primarily attributed to the air being pushed in the locomotive area and the negative pressure from the vortex structure between trains. When the speed is increased from 350 km/h to 400 km/h, the aerodynamic load on the train increases by approximately 20 % to 40 %, and the acceleration of the head train grows by 20 % to 50 %. The most noticeable decrease in ride comfort is observed in the head train, with the highest increase in the head train’s Overall Vibration Total Value (OVTV), which rises by 30.1 %.

Advanced heave control of a hydrofoil-based autonomous surface vehicle: CFD modeling with integrated variable propeller revolution control

An innovative control strategy employing the Proportional-Integral-Derivative (PID) algorithm is proposed to address the heave stability challenges in the in-house developed hydrofoil-based Autonomous Surface Vehicle (HASV). This method regulates the HASV's heave motion by adjusting the propeller's revolution speed. After confirming that the aerodynamic load on the superstructure contributes less than 2% compared to the hydrodynamic load, a detailed numerical simulation study and recirculating water tunnel test were conducted to validate the reliability of the established Unsteady Reynolds-Averaged Navier-Stokes (URANS) CFD model for the HASV substructure. The integration of the PD controller for propeller revolutions into the CFD free-running model, which incorporates fully nonlinear and viscous effects, was achieved using the ‘Region-Moving’ method for the background domain and the Body Force Method (BFM) for the propeller domain. By analyzing the impact of various PD coefficients on heave control, optimal settings for the HASV were determined. Subsequent studies examined the vehicle's capability in draft correction and draft maintenance under wave conditions. The results of direct CFD-PD simulations demonstrate that the proposed heave control method effectively stabilizes the HASV under complex nonlinear environmental conditions, offering valuable insights for addressing similar heave control challenges in hydrofoil-based vehicles.

Optimization flutter response of laminated smart nanocomposite truncated conical shell under supersonic aerodynamic pressure using hybrid IGWO-DQHFEM

Given the wide application of conical shells in the aerospace and aircraft industry, there comes a need for dynamic analysis and optimum design of these structures against supersonic aerodynamic forces, which induce a phenomenon called flutter. As the key contribution of this paper, a new method has been developed and applied to optimize the dynamic and flutter control of truncated conical shells under supersonic aerodynamic loads. Here, a truncated conical shell with a layered configuration is considered for the optimization of supersonic aerodynamic conditions with smart control, shape, and size optimum design, wherein every layer is reinforced with carbon nanotubes (CNTs). Moreover, a conical shell is considered with piezoelectric properties to smartly control the aerodynamic behavior of the structure, so by applying voltage, it will be possible to control flutter or critical aerodynamic pressure and frequency. The objective of the optimization model is defined based on aerodynamic pressure and frequency of conical shells. Mathematical modeling of the structure with high accuracy is carried out to optimize the model. The supersonic aerodynamic force is considered employing piston theory, where seven variables are used through a high-order shear deformation theory. In the new numerical method, the differential quadrature hierarchical finite element method (DQHFM) is used for the solution of the coupled electro- dynamic equations of the structure and computing the frequency of the structure along with the flutter or critical aerodynamic pressure. The optimization model obtained by the DQHFM method is applied to search the optimum conditions using an Improved Grey Wolf Optimization (IGWO) method. In IGWO, the local search condition is proposed based on the optimum positions and statistical properties of agents in previous positions. Finally, the optimum size, shape, and smart control parameters of the structure such as the length and radius of the cone, cone apex angle, external voltage, CNTs volume fraction, number of layers, and airflow angle are drawn out and discussed by IGWO and DQHFM. The results show that by increasing the cone angle from 30 o to 60 o, the optimum voltage that has to be applied decreases. On the other hand, an optimal radius stabilizes at around 1 m and the optimum volume fraction of the CNTs is 10 %.

Aerodynamic and aeroacoustics investigation of tandem propellers in hover for eVTOL configurations

The present study investigates the aerodynamic interactions and the aeroacoustic footprint of a tandem propellers configuration typical of a multi-rotor eVTOL aircraft in hover conditions. In particular, an experimental campaign was conducted to collect a comprehensive aerodynamic and aeroacoustic database over two scaled propellers models in tandem. Aerodynamic loads and acoustic measurements were performed in an anechoic test chamber. Measurements also included flow field surveys using stereoscopic PIV technique. The configurations tested included twin propellers in side-by-side and staggered configurations with partial overlap between rotor disks. The activity was completed by numerical simulations performed with the mid-fidelity aerodynamic solver DUST. The analysis of experimental and numerical results enabled to provide a robust comprehension of the different flow mechanisms that characterise aerodynamic interaction between propellers wakes by changing longitudinal and lateral distances as well as blades sense of rotation. In particular, the effects of these interactions on both the aerodynamic performance and aeroacoustic footprint was investigated. Specifically, the partial overlap between propellers disks leads to a conspicuous reduction of aerodynamic performance of the propeller invested by front propeller slipstream as well as an increase of the acoustic emission of the dual propeller system.

Three-component aerodynamic load cells

Three-component aerodynamic load cells

Characteristics of Sudden Change in Aerodynamic Load of High-Speed Train Caused by Wind Barrier and Its Buffer Measure

When high-speed trains (HSTs) rapidly enter or exit the wind barrier area of the bridge, the quick change in the operating environment can lead to sudden changes in train aerodynamic loads, resulting in the deterioration of their aerodynamic performance and adversely affecting safe and stable operation. In this paper, the effects of wind barrier porosity, crosswind speed, and train speed on the sudden change in the aerodynamic load of the HST induced by wind barriers are analyzed, and the reasons for the sudden change from a flow field perspective are given. Additionally, the influences of the buffer structure with three lengths of 45 m, 90 m, and 135 m on the sudden change in the aerodynamic load of HSTs are studied. The results show that the lower the porosity of the wind barrier, the higher the crosswind speed, and the lower the speed of trains entering and exiting the wind barrier area, resulting in a greater degree of sudden change in the aerodynamic load of the HST. The buffer structure measuring 90 m in length is considered the most suitable, as it can significantly alleviate the sudden change in the aerodynamic load and effectively enhance the safety of train operations.

On the Effect of Current Stabilizer on Dynamics of a Small Hybrid Wind Power Generator

The use of small wind power generators remains quite relevant. In particular, they can be efficient for charging batteries in remote locations where there is no centralized power supply (including in the Arctic, Far East, etc.). They can also be used as part of missions to planets with atmospheres. One of the promising design solutions for a small wind power generator with a vertical axis of rotation is a hybrid device. It consists of two wind turbines that have a common axis of rotation: external (Darrieus wind turbine) and internal (Savonius rotor). This scheme represents a compromise between the relatively high power coefficient of the Darrieus turbine and the good startup characteristics the Savonius rotor. It is known that one of the typical battery charging modes is constant current charging. Here we consider a hybrid installation, the generator of which is connected to a current stabilizer. The load is simulated with an active resistance. It is assumed that the generator is a DC generator. A closed mathematical model of the studied system is constructed. The aerodynamic load is described using the quasi-steady approach. It is assumed that the characteristic time of electrical processes is much smaller than the characteristic time of mechanical processes. The influence of load resistance on the behavior of the system is investigated. It is shown that, under certain conditions, several steady modes (up to five) exist in the system. In this case, at least two of them are attracting. Therefore, the hysteresis of the angular speed of the steady mode is possible when the load resistance changes. It should be noted that in a number of situations, an unstable steady mode (which corresponds to a lower angular speed of the turbine than a stable one) may be preferable (for example, to reduce the load on bearings). In this regard, a resistance control strategy has been proposed to ensure stabilization of the unstable stationary regime.

Study Of Tandem Rotor Dual Wake Interaction With Downstream Stator Under Unsteady Numerical Approach

Abstract This paper highlights the intricate rotor-stator interaction between a tandem bladed rotor and a single-bladed stator in the light of unsteady numerical simulations. A low speed tandem bladed compressor stage has been conceptualized and experimentally validated against targeted performance goal. With the evident pressure rise capability of the tandem bladed compressor stage, it becomes obligatory to investigate the rotorstator interaction owing to its dominant effect on overall stage performance. The multi-passage rotor-stator unsteady simulations have been performed using blade transformation methods in ANSYS CFX. Due to the presence of two highly loaded rotor blades, the tandem rotor exhibits peculiar rotorstator interaction in terms of multiple wake impingement on the stator. Incorporating tandem blading on the rotor instead of the stator (which is more common) constricts the design envelope in terms of choice of blade axial overlap and percentage pitch. The variation of aerodynamic loading from hub to tip for both the rotor blades results in spanwise varying wake strength. The initially distinct wake structures merge resulting into a thicker wake. Additionally, the rotor blades are highly loaded in the tip region which results in the complex interaction between end-wall boundary layer and tip leakage flow. Cumulatively, these conditions constitute a challenging aerodynamic field for the downstream stator. The study focuses on the qualitative interaction between the rotor wakes and blockage with the downstream stator and put forwards some aspects of the tandem rotor-single stator stage design especially for core compressors of aero engine application.

A Comparison of the Capture Width and Interaction Factors of WEC Arrays That Are Co-Located with Semi-Submersible-, Spar- and Barge-Supported Floating Offshore Wind Turbines

This research paper explores an approach to enhancing the economic viability of the heaving wave energy converters (WECs) of both cylinder-shaped and torus-shaped devices, by integrating them with four established, floating offshore wind turbines (FOWTs). Specifically, the approach focused on the wave power performance matrix. This integration of WECs and FOWTs not only offers the potential for shared construction and maintenance costs but also presents synergistic advantages in terms of power generation and platform stability. The study began by conducting a comprehensive review of the current State-of-the-Art in co-locating different types of WECs with various foundation platforms for FOWTs, taking into consideration the semi-submersible, spar and barge platforms commonly employed in the offshore wind industry. The research took a unified approach to investigate more and new WEC arrays, totaling 20 configurations across four distinct FOWTs. The scope of this study’s assumption primarily focused on the hydrodynamic wave power performance matrix, without the inclusion of aerodynamic loads. It then compared their outcomes to determine which array demonstrated superior wave energy under the key metrics of total absorbed power, capture width, and interaction factor. Additionally, the investigation could serve to reinforce the ongoing research and development efforts in the allocation of renewable energy resources.

The aerodynamic load experienced by an igloo under varying wind angles

Abstract. In this project, I investigated the aerodynamic load acting on an igloo structure when it is subjected to different wind angles. By using Computational Fluid Dynamics (CFD) simulations on COMSOL Multiphysics, I first analyzed a simple 2D cylinder case as a way to learn the software. After that, I studied a sample CFD case of a NACA 0012 airfoil that is published under the COMSOL website. Finally, I moved on to create my own igloo CFD case to study its aerodynamic load under varying wind angles (0-30 degrees in 3-degree increments). Understanding the aerodynamic load of this sample igloo can be useful in learning how igloos behave in extreme weather conditions and fast wind velocities. It is also beneficial to know when will the igloo experience the least force when built under a non-level surface and the wind is hitting the structure at an angle.

Investigation of dynamic stall models on the aeroelastic responses of a floating offshore wind turbine

Dynamic stall effects significantly affect the aerodynamic load prediction of wind turbines. In order to investigate the dynamic stall effects on the loads and responses of a 15 MW floating offshore wind turbine (FOWT), a novel dynamic stall model, namely IAG, is implemented within the widely-used simulation software package OpenFAST in this study. The superiority and accuracy of the IAG model are verified by comparisons against experimental data and numerical results from the Beddoes-Leishman (B-L) model. The results have shown that the IAG model is able to more accurately capture edges of the hysteresis loops of aerodynamic coefficients corresponding to various airfoils and operation states. The aeroelastic responses of a 15 MW floating offshore wind turbine under normal and extreme environmental conditions are calculated by employing the IAG model. The impact of dynamic stall models on blade loads and displacements has been analyzed. It is found that the B-L model produces larger loads and displacements under high wind speed and yaw error conditions, attributed to the insufficiently computational robustness of the B-L model under deep stall situations and the seriously dynamic stall circumstances. The 1st-order and 2nd-order bending modes of the blade are expected to be enhanced by the aerodynamic loads that are predicted using the B-L model. Consequently, the bending-torsional coupling effects would be enhanced, leading to an increase up to 64.7 % on the in-plane bending moment. This study has confirmed that the dynamic stall model should be properly selected properly for the fully coupled analysis of FOWTs.

Fluid-thermally-solid coupling analysis of aircraft leading edge

Abstract Aircraft are affected by aerodynamic loads during operation. To analyze the impact of the leading edge structure of aircraft under different flight angles of attack, this paper uses the fluid-heat-solid coupling calculation method. It combines CFD with the thermal-structure field solver and uses simulation software, with a flight altitude of 15 km, flight speed of 6 Ma, and flight Angle of attack of 0 ~ 20°. Considering the change of material parameters with temperature, the coupling of multiple physical fields in aircraft is simulated and analyzed. The simulation results show that the existence of the flight angle of attack makes the flow field shock wave position of the aircraft closer to the windward surface of the structure. The angle of attack exacerbates the structural deformation of the aircraft, with the maximum deformation occurring at a 20° angle of attack, which is 3.06 mm. The research results can provide a reference for aircraft design.

Hybrid Testing System Development for Single Point Mooring Lines FOWT’s

Abstract To advance the development of various concepts for floating offshore wind turbines, it is imperative to have access to experimental data. These data are used in the validation of the tools for the simulation of floating turbines and also for the tuning of the models. CENER has developed a hybrid testing methodology that enhances the performance of wave basin tests for scaled models of Floating Offshore Wind Turbines (FOWTs). This approach allows us to apply forces and moments from the wind turbine to the floating platform without needing to replicate wind within the testing facility or create a complex model of the wind turbine rotor. However, when it comes to testing single point moored (SPM) platforms, a unique challenge arises. These platforms have an additional degree of freedom as they can freely rotate around the vertical axis of their mooring attachment (yaw degree of freedom). These type of platforms can present important misalignments with respect to the wind depending on the combination of wind, wave and current directions. Consequently, accurately capturing the impact of misalignment on platform dynamics, especially in yaw, is essential to assess the platform’s ability to self-align with the wind direction, a key factor known as weathervaning capacity. The X1Wind platform is an innovative floating wind system, based on a single point mooring solution with a downwind wind turbine configuration that allows it to be passively self-orientated. The concept has been extensively tested on prototypes at real sea conditions as well as on scaled models at wave basins. For the last wave basin testing campaign, X1Wind has entrusted CENER with the development of the hybrid testing methodology adapted to the requirements of SPM platforms. The testing campaign has covered different wave and wind conditions, including misalignment scenarios and has shown a good dynamic behavior of the platform on yaw. This study outlines the advancements made in the CENER Software-in-the-Loop (SiL) hybrid testing system for wave basin tests of SPM platforms. In order to correctly introduce the direction of the aerodynamic forces on the wind turbine under misaligned conditions, improvements on the software and hardware (loads actuator) of the SiL system were developed and tested. An actuator system consisting of 6 propellers was used. The numerical model that calculates the rotor aerodynamic loading were expanded to take into consideration the direction of the aerodynamic loads with respect to the platform. Additionally, the drag of the wind over the tower and other platform elements must be considered, as they can play a relevant role in the generation of the weathervaning moment. The study concludes that the use of the upgraded SiL hybrid testing system is an effective and afordable solution for the testing of scaled SPM platforms at wave basin facilities. It also summarizes the different considerations that the system has to overcome for the particularity of this type of testing application.

Approaches and Challenges in FEED and Detailed Design Process of Floating Substructures

Abstract In the FEED or detailed design phases, the floating foundation designers have to deal with complex structural design aspects and meet certification or class requirements for structural verifications, such as yield and buckling checks as well as fatigue checks for steel structures. The designer faces several challenges during the structural verification process, starting with the accurate definition of the complex external load state with the simultaneous action of aerodynamic, hydrostatic and hydrodynamic loads, inertia and mooring loads, followed by the processing and handling of very large load case tables required for the analysis of floating wind turbines, down to time efficient post-processing of the analysis results compatible with typical commercial project schedules. The paper discusses some of the currently existing and applied methodologies on how the structural checks are typically performed in these circumstances, and addresses their advantages and shortcomings. In addition, a new Global Influence Superposition (GIS) methodology that has been developed by Ramboll is presented, which is able to address many of the existing challenges in an efficient manner.

Monitoring the Wake of Low Reynolds Number Airfoils for Their Aerodynamic Loads Assessment

Experimental investigations are carried out to explore the aerodynamic performance and vortex shedding characteristics of S5010 and E214 airfoil-based wings to provide guidance for the design of MAVs and other low-speed vehicles. Force and wake shedding frequency measurements are carried out in a subsonic wind tunnel in the Reynolds number (Re) range of 4 × 104 - 1 × 105. The measurements with increasing Re show that the slope of the lift curve in the linear region increases by 14% for S5010, while this increment is 11% for E214. The peak lift coefficient of both airfoils reduces with reducing Re. For lower pitch angles, the influence of Re on drag coefficients is less significant, but at higher angles, the drag increases as the Re drops. Unlike pre-stall mountings, the pitch-down propensity of the airfoil enhances in the post-stall region for high Re flows. Moreover, the frequency of shed vortices reduces with rising angle of attack at a given Re. In contrast, the Strouhal number almost remains constant with varying Re at a fixed angle of attack. For S5010 and E214 airfoils, the Strouhal number is noticed to vary between 0.68 - 0.36 and 0.58 - 0.36, respectively, for pitch angle variation of 12°- 28°. The airfoils show a higher Strouhal number than the bluff body wakes, but this difference decreases for high angles of attack mountings. This finding reveals that the wake structure of the airfoil at a high post-stall angle behaves as bluff body wakes.

Aeroacoustic Analysis of Rotor in Forward Flight Considering Blade Elastic Deformation

Abstract A rotor aeroacoustic calculation model of the rotor in forward flight based on CAMRAD II and FW-H equation was established, which can involve blade elastic deformation. CAMRAD II was used to calculate the actual motion of the blade and the rotor’s unsteady aerodynamic load based on the elastic blade model. The blade dynamics module in the noise calculation program was replaced to consider the blade elastic deformation in forward flight based on the FW-H equation. The forward flight noise characteristics of a full scale rotor were researched. The research shows that the rotor has obvious torsion and flap elastic deformation. The blade elastic deformation has little effect on the directivity of noise in forward flight. In the main noise propagation direction, blade deformation affects the loading noise, resulting in a maximum variation of 3.0dB or more in total noise. In noise calculation, the accuracy of noise prediction can be improved by matching the position of the real blade tip.