Wind Tunnel Tests Research Articles

Self-excited force characteristics and flow mechanisms of a 5:1 rectangular cylinder in torsional vortex-induced vibration and flutter

In this paper, the self-excited force characteristics, flow rules and vibration mechanisms of a 5:1 rectangular cylinder in torsional vortex-induced vibration (VIV) and flutter were investigated through wind tunnel tests and numerical simulations. The nonlinearity of the self-excited lifting moment is not monotonous but exhibits a peak within a specific reduced wind speed and amplitude range. The amplitude-dependent characteristics of dimensionless work and aerodynamic damping are the primary reasons for non-divergent vibration, which is mainly influenced by the amplitude-dependent phase difference. The reduced wind speed significantly affects the formation zone length and convection speed of the leading-edge vortex, thereby determining the distribution of surface pressure phase difference and dimensionless work. As the reduced wind speed increases, there is a positive and negative alternation in dimensionless work, leading to the occurrence of torsional VIV and flutter. While the torsional amplitude does not affect the distribution of phase difference, it merely influences the formation zone length, resulting in amplitude-dependent dimensionless work and accounting for the non-divergent vibration. The characteristics of vortex convection, pressure phase variation and dimensionless work of the 5:1 rectangular cylinder in torsional VIV and flutter follow similar rules, indicating that the two vibration forms share the same inherent essence.

Study on dynamics and power generation performance coupling of galloping-based triboelectric nanogenerator for harvesting broadband wind energy

In order to innovate the wind energy harvesting method based on galloping and improve galloping-based triboelectric nanogenerator wind energy harvesting performance, a galloping-based square cylinder triboelectric nanogenerator (GSC-TENG) is proposed in this work. The GSC-TENG consists of a square cylinder bluff body, a triboelectrification embedded in the bluff body, a cantilever beam and a base. The response of the aerodynamics and power generation performance of the GSC-TENG with a high mass ratio (m*=526.6) to the system damping ratio (0.0106, 0.0304 and 0.0568) and wind speed (0.6–12.4 m/s) are studied through CFD simulation and wind tunnel test. The critical wind speed, amplitude and power generation performance of systems with different damping ratios are analyzed in detail, and the wind speed range corresponding to the maximum amplitude is determined. By increasing the stiffness and damping ratio of the system, the output performance under high wind speed conditions can be enhanced and stabilized. Compared with the GSC-TENG with damping ratio 0.0106, the output power of the GSC-TENG with damping ratio 0.0568 at the wind speed of 4.0 m/s is enhanced by 141 times, which is up to 62.25 W/m3. To harness a broadband wind energy, a novel galloping-based TENG is introduced. Analyzing the dynamic characteristics of square cylinder bluff body with different damping ratios is of significant meaning to the design and improve of the galloping-based triboelectric wind energy harvester.

Streamline curvature effects generated by tornado-like flows on the aerodynamics of a low-rise structure

This paper examines the streamline curvature effects on the aerodynamic pressure patterns induced by tornado-like flows on a low-rise structure. The analysis derives from the detailed scrutiny of a wind tunnel test campaign carried out at the WindEEE Dome tornado simulator. The simulated tornado-like flows were characterized by a swirl ratio such that the cores were characterized by multiple vortices. The tornado-like vortex was slowly translated across the chamber of the simulator. Surface pressure measurements were acquired on both the building model surface and on a circular ground plate around it, and synchronized with velocity measurements gathered from four Cobra probes installed in the proximity of the corners of the structure. These Cobra probes allowed the definition of the tornadic streamlines. Multiple nominally identical repeats were carried out to gather a robust estimation of conditionally-averaged pressure and velocity measurements based on the position of the tornado-like vortex. When comparing different cases characterized by similar conditions of upstream wind direction, the mean aerodynamic pressure patterns were revealed to be sensitive to the streamline curvature. Moreover, these are distinct than those generated from straight-line ABL winds, consistently calibrated upon the measurements from the Cobra probes in the upstream proximity of the building.

Field measurements reveal insights into the impact of turbulent wind on loads experienced by parabolic trough solar collectors

To ensure efficient and reliable operation of a concentrating solar-thermal power (CSP) plant, its solar collector field needs to accurately focus sunlight. The optical efficiency and structural integrity of the solar collectors is significantly influenced by wind conditions in the field. In this study, we present insights into dynamic wind loading on parabolic trough CSP collectors. We derive novel conclusions by analyzing a first-of-a-kind measurement campaign of wind and structural loads, performed at an operational CSP plant. Previous research primarily relied on wind tunnel tests and simulations, leaving uncertainty about wind loading effects in operational settings. We demonstrate that the parabolic trough field significantly alters the turbulent wind field within the collector field, especially under winds perpendicular to the trough rows. Our measurements within the trough field show reduced wind speeds, changes in wind direction and turbulence properties, and vortex shedding from the trough assemblies. These modifications to the wind field directly impact both static and dynamic support structure loads. Our measurements reveal higher wind loads on trough assemblies compared to those observed previously in wind tunnel tests. The insights from this study offer a novel perspective on our understanding of wind-driven loads on CSP collectors. By informing the development of next-generation design tools and models, this research paves the way for enhanced structural integrity and improved optical performance in future parabolic trough systems.

Sustainable Manufacturing of Multifunctional Fluorine-Free Superslippery Flexible Surfaces.

Surface contamination and friction result in significant energy losses with widespread environmental impact. In the present work, we developed fluorine-free super-slippery surfaces employing environmentally friendly and simple biofuel-based flame treatment of polydimethylsiloxane (PDMS). Through a unique combination of processing parameters, highly transparent (>90%) and flexible films were engineered with omniphobic, anti-icing, and ultra-low friction properties. The processed films showed an extremely low tilting angle (<5°) and contact angle hysteresis (<4°) against different liquids, even under subzero temperatures. The coefficient of friction (COF) reduced to 0.01 after processing compared to ∼1 for PDMS. Extremely low ice adhesion of <20 kPa and enhanced freezing time ensured anti-icing behavior. The exceptional multidimensional traits were derived from the extremely stable silicone lubricant layer ensured by the hierarchically structured wrinkles. Wind tunnel tests showed that an air drag velocity of less than 0.5 m/s was sufficient to initiate droplet motion, highlighting low interfacial friction that leads to an anti-staining nature. Sustaining the self-cleaning and anti-staining characteristics, the processed surface showed utmost durability under different harsh conditions. The super-slippery surfaces with multifunctional characteristics fabricated through a sustainable route can be effectively used for various engineering and industrial applications.

The study of cascading effect in the integration of intake with gas turbine engine bay in subsonic cruise vehicle

Abstract Submerged air intake is often acquainted with the merit of reducing the drag and fitting well within the frame of weight constraints imposed on subsonic cruise vehicle. A novel method for designing an Intake was developed by GTRE, which has been successful with the validation against wind tunnel testing. The designed intake has been integrated with engine bay area of subsonic cruise vehicle. In this study, a provision of bleed from the ramp surface of the intake into the bay through splitter is used for cooling the engine frame, mechanical fixtures, oil tank and other electronic instruments mounted around the engine frame. Different sets of cowl ventilation slots provided on the bay wall will effuse this by-pass air from the intake into the atmosphere there by influencing the heat distribution within the bay area. The cascading effect of the intake with the bay area is extensively studied in this paper.

Investigation of the wind loads and flow patterns of a high-rise building under twisted wind flows based on LES

The twisted wind effect has attracted increasing attention among scholars due to its significant influence on the wind loads and wind induced responses of high-rise buildings. Nowadays, it is still challenging to simulate twisted wind flows (TWFs) with larger wind twist angles (WTAs) in the wind tunnel test. Compared to wind tunnel test limitations, the large eddy simulation (LES) offers an effective tool to simulate a broader WTA range. Several state-of-the-art numerical studies have generated TWFs that rely on multiple velocity inflow boundary (MVIB), but it results in vast computational domains and substantial abnormal pressure fluctuations. This paper proposes a single velocity inflow boundary (SVIB) method for modeling TWFs, which can significantly reduce the computational domain size without losing accuracy. Based on the SVIB method, we simulate TWFs with four WTAs (i.e., 0°, 25°, 35°, 45°) and conduct a comprehensive analysis of the influence of WTA and wind direction angle on both the wind load characteristics of and the flow patterns around a high-rise building. The results show that the TWFs will twist the vortex topology and trajectory, and the maximum extreme local resultant force coefficient under 35TWF is larger than that under SWF by around 10 %. The positive and negative wind pressures can simultaneously occur on a special surface at large WTAs (e.g., 35°, 45°), which may impose significant shear forces on the intermediate layers. The wind veering effect enhances the contribution of vortex shedding to the longitudinal fluctuating wind loads and the influence of incoming turbulence on lateral fluctuating wind loads. This study contributes to providing a more effective LES method to simulate TWFs with large WTAs and to reveal the effect of large WTA on the wind load characteristics of high-rise buildings under TWFs and the underlying flow mechanism, which is beneficial to the future wind-resistant design of skyscrapers.

Surface roughness effects on transonic aircraft performance: Experimental/numerical comparisons

This work highlights the necessity of taking into account surface roughness when conducting experimental tests, and when using numerical simulations to precisely calculate the turbulent lift and drag of wind-tunnel models or real aircraft in transonic conditions. The present article is a continuation of “Turbulent drag induced by low surface roughness at transonic speeds: Experimental/numerical comparisons,” Physics of Fluids, Vol. 32, 045108 (2020) by Hue and Molton. The outcomes of this former study, which was focused on flat plate samples, are here applied to a three-dimensional aircraft configuration: the Common Research Model used as a reference in the recent international Drag Prediction Workshops. Experimental campaigns have been performed in the largest ONERA wind tunnels S1MA and S2MA involving models with average surface roughness heights Ra close to 0.5 micrometers, wingspans up to 3.5 meters, Mach and Reynolds numbers up to 0.95 and 5 million respectively. Reynolds-averaged Navier–Stokes computations based on the wind-tunnel tests have then been carried out, using the equivalent sand-grain roughness height approach as well as a Musker-type correlation to determine relevant ks values. The results of both the experimental and numerical campaigns have demonstrated that the aerodynamic coefficients of the aircraft can be significantly affected by the surface roughness, even with roughness Reynolds numbers ks+ potentially below the usual threshold values sometimes considered in engineering applications (i.e. in the order of 3.5 to 5). In particular, the surface roughness effects on lift and drag have been studied using far-field analyses to evaluate the responses of friction, viscous pressure, wave and lift-induced drag components. Finally, the numerical studies have been extended to the full-scale geometry in flight conditions in order to assess the roughness effects and potential gains in realistic aircraft operating conditions.

Wind loading on gable and multi-span roof buildings: Comparison between field monitoring, wind tunnel experiments, and design code provisions

The wind loading provisions in the National Building Code of Canada (NBCC) have not been updated for decades despite developments in wind tunnel methods since the original source data. This study aims to review the Nbcc 2020 provisions compared to wind tunnel experiments, field measurements, and the ASCE 7–22 provisions for single and multi-span gable roof buildings. Field measurements and wind tunnel tests are used to collect data for an isolated building and later for a multi-span gable. The pressure coefficients from the field measurements were mostly higher than the wind tunnel, which is consistent with previous studies. The results provided evidence that NBCC provisions for single-gabled roofs (with slope 7∘<α≤27∘) and multi-span gabled roofs (with slope 10∘<α≤30∘) are currently underestimated. New provisions are suggested for the corner (c), edge (s), and field (r) zones of the single-span gabled roof and for gable-end-edge (s’) zone of the multi-span. It is suggested to merge Zone s into Zone c to form a new perimeter Zone p for the single gabled roof and to merge Zone s’ into Zone c for the multi-span gabled roof. The proposed changes correct the current provision underestimation and add simplicity for easier construction.

Numerical and experimental investigations of diffusion-induced boundary layer separation on aero-engine nacelles

Aero-engine nacelles have to fulfill design requirements at both cruise and off-design conditions. Under engine windmilling conditions the ingested streamtube massflow is relatively low. A key off-design condition is take-off, which, in conjunction with an engine windmilling scenario, results in the stagnation point of the ingested streamtube being located significantly inside the intake. The combination of high angle of attack and low engine massflow rates leads to a strong flow acceleration and subsequent diffusion of the boundary layer on the upper quadrants of the external nacelle cowl, which can terminate with subsonic separation from the leading-edge. Under this condition, Reynolds number effects can play a dominant role on the separation onset and characteristics and 3D-annular wind tunnel tests cannot always achieve Reynolds’ number equivalent to full scale. A novel quasi-2D rig configuration representative of the aerodynamics of a full-size aero-engine nacelle under windmilling end of runway conditions examined in detail the characteristics of the boundary layer on the external cowl of a nacelle prior to diffusion-induced separation. Separation of the boundary layer was independently promoted through changes to represent different engine massflow rates and freestream Mach number on the rig to determine the limits of steady Reynolds Averaged Navier Stokes (RANS) methods to discern the onset of boundary layer separation. For the conditions and geometry investigated, the combined experimental and computational results showed that there was laminar to turbulent transition of the boundary layer ahead of the subsonic diffusion. The work showed that steady RANS can predict the onset of boundary layer separation with an uncertainty of approximately 10% on notional engine massflow rate and 0.05 on freestream Mach number relative to a nominal operating freestream Mach number of 0.25. This provides guidance for the industrial design and optimization of future windmilling-tolerant nacelles for large ultra-high bypass ratio turbofan engines.

Intelligent evaluation of interference effects between tall buildings based on wind tunnel experiments and explainable machine learning

The interference effects of taller high-rise buildings significantly impact the nearby shorter high-rise buildings in dense urban areas, potentially leading to severe wind-induced disasters. This study aims to develop a universal intelligent assessment method to predict the aerodynamic forces and wind-induced responses of buildings, considering various interfering and coupling factors. A database containing 61440 samples is established through a series of synchronous pressure measurement wind tunnel tests. The aerodynamic forces and wind-induced responses were predicted using six machine learning models under varying wind fields, interfering building locations, interfering building sizes, and dynamic characteristics of the principal building. The performance of the models was enhanced through Bayesian hyperparameter optimization and evaluated using the R2 and NRMSE. Additionally, the SHapley Additive exPlanations (SHAP) method was applied to evaluate the impact of each factor on the aerodynamic force and wind-induced response coefficients. Eight specific cases were examined using local SHAP explanations to explore the influence of seven input variables on maximum wind-induced response coefficients. Results indicated that the XGB model exhibited superior predictive performance, with R2 exceeding 0.99 in both training and testing sets. The SHAP analysis revealed significant impacts from wind direction angle, reduced wind speed, and damping ratio on wind-induced response. Consequently, irrelevant or minimally impactful input variables were removed from the XGB models. The R2 and NRMSE variation rate with reduced inputs for the optimized XGB model was less than 0.45 %. The graphical user interface (GUI) was designed can effectively guide intelligent urban planning and building design.

On the accuracy of idealized sources in CFD simulations of pollutant dispersion in an urban street canyon

Idealized pollutant sources are widely used by the scientific community to replicate traffic emissions in wind tunnel tests and CFD simulations. However, it is unclear to what extent such idealized sources can adequately reproduce the emission and dispersion by cars in idle (static) or moving situations in streets. This study investigates the impact of a static idealized point source (S-IPS) versus an idling or static (S-) and a moving or dynamic (D-) realistic car source (RCS) on the pollutant dispersion in a street canyon. First, 3D steady RANS and LES simulations are performed with a S-IPS and validated by means of wind-tunnel tests. Next, LES simulations are performed to analyze the impact of S-IPS versus S-RCS. Finally, three D-RCS with different car speeds are simulated and compared with S-RCS. The results show that using a S-RCS increases the plane-averaged concentration by 11%–140 % at z/H = 0.03 and by 30%–50 % at y/H = 0, with respect to S-IPS. The comparison of S-RCS and D-RCS shows that car movement can also have a large impact on pollutant dispersion along the canyon.

Aerodynamic Behavior of Hump Slab Track in Desert Railways: A Case Study in Shuregaz, Iran

The development of rail transport necessitates expanding environmentally friendly infrastructure. However, specific challenges arise in desert and sandy regions. One innovative solution to manage the effects of windblown sand on desert railways is the use of hump slab track superstructure. This paper develops a solid–fluid aerodynamic model based on ANSYS Fluent 2021 R2 software to simulate the hump slab track during a sandstorm. The model is validated through wind tunnel testing. A case study of a railway sandstorm in the Shuregaz region of Iran is presented, evaluating various sandstorm parameters and hump heights to determine their impact on sand concentration and particle velocity within the sand transit channels. The results indicate that increasing the sand particle diameter (from 150 to 250 µm) leads to higher sand concentration (up to 40%) and lower sand movement velocity (up to 28%). These results have been observed with a higher incremental approach concerning the sand flow rate. Conversely, increasing sandstorm velocity (from 10 to 30 m/s) decreases sand concentration and increases sand movement velocity up to 80% and 150%, respectively. Additionally, a 25 cm hump height significantly enhances sand passage by creating larger channels.

A new controllable weak recycling inflow turbulence generator for evaluating wind effects on building in LES

The weak recycling method, known as the “rescaling-recycling” method, has been extended to simulate micro-scale turbulent atmospheric boundary layers (ABL) by employing staggered blocks in the developing section, replicating physical ABL wind tunnel setups. However, this method faces challenges, such as the need to re-evaluate the sizes and configurations of roughness elements when addressing different objective structures, computational domain sizes, or ground exposures. To address these issues, we propose a controllable weak recycling (CWR) method for generating turbulent ABL flows over rough surfaces in large eddy simulation (LES). This method can directly produce a turbulent boundary layer with arbitrary target characteristics in a single simulation, significantly enhancing generation efficiency and reducing computational resource consumption. Our refinement method incorporates a feedback proportional control algorithm into the “rescaling” procedure to minimize errors between simulated and targeted turbulence intensities. Besides, an existing drag model is utilized in the near-ground region to maintain horizontal homogeneous ABL flows over rough surfaces. The proposed CWR method is validated by simulating three turbulent ABL flows over various rough terrains using LES. Results confirm that the generated inflow turbulence adheres to prescribed mean velocities and turbulence intensities, demonstrating consistent self-sustainability along the flow direction. Furthermore, the generated wind spectra closely align with the anisotropic von-Kármán spectrum. When applying the extracted wind time histories at the main domain’s inlet, we find that the mean and fluctuating wind pressures on a high-rise building closely match specified wind tunnel test results.

Aerodynamic optimization of high-rise building with façade ribs through CFD-based multi-objective optimization algorithm

Façade appurtenances is an effective aerodynamic optimization measure for alleviating the wind loads on high-rise buildings in modern cities, while the optimized layout of façade ribs necessary for practical engineering remains unclear. The conventional method through numerical simulations and wind tunnel tests can only obtain limited optimal schemes of ribs, the optimization process is time-consuming and laborious, an optimization algorithm can be used to effectively evaluate the optimal arrangement of façade ribs. In present study, a multi-objective optimization procedure coupling large eddy simulation (LES), back propagation neural network (BPNN), and non-dominated sorting genetic algorithm (NSGA-II) is applied to evaluate the optimal arranged parameters of façade vertical ribs. The optimization procedure can quickly identify the optimal location parameter b and extensional depth d of façade ribs that producing minimum wind loads acting on building and ribs. The findings indicate that there are complex non-linear relationships between the ribs arrangement parameters and the objective wind loads. The mean drag C‾d and fluctuating lift C'l of models of windward ribs and upstream sidewall ribs have opposite trend. The relationships between wind forces and arranged parameters of the downstream sidewall and leeward ribs are relatively complicated due to the vortex shedding. Genetic algorithm NSGA-II can effectively evaluate the optimal trade-off solution among multi-objective wind loads. The ranges of optimal layout parameters b/D and d/D are 0.14–0.17, 0.073–0.077, the ratio of b/d is about 2, and the optimal arrangement of façade ribs well balances the total wind forces on the model and wind forces on the ribs. The 3D numerical simulations demonstrate that the optimal layout of the ribs can considerably improve the flow structure and wind load, the maximum reduction ratio of the C‾d and C'l are achieved 25 % and 56 %, respectively. The obtained optimized layout parameters can provide reference for engineers when actually using the facade ribs.

Investigating Flow-Induced Vibration by Regarding the Alignment of Flow Modes and Structural Modes

In this work, a modal matching approach is developed to investigate the impact of the spatial correlation of wall pressure fluctuations on structural vibration and its role in suppressing flow-induced vibration in aircraft. The modal matching method defines the wavelength ratio between the convection wave and the flexural wave to capture the spatial characteristics of both the flow mode and the structural mode. In comparison to conventional methods such as the finite element method and analytical method, the proposed modal matching approach allows for obtaining the vibration response in the spatial–wavenumber domain. To validate the spatial correlation effect on structural vibrations obtained with the modal matching approach, a wind tunnel test was conducted to measure flow-induced vibrations. The calculated spatial–wavenumber data for flow-induced vibrations reveal that the crests and troughs of the vibration velocity alternate periodically as the wavelength of the wall pressure fluctuations changes. At the resonance frequency, a vibration velocity trough can be observed when the spatial correlation of wall pressure fluctuations aligns with the structural mode. Additionally, the concept of resonance independence of flow-induced vibrations is introduced to describe the phenomenon where the most severe structural vibration, determined by the matching value between the aerodynamic mode and the structural mode, does not always occur at the resonance frequency. The modal matching approach effectively suppresses structural vibration by utilizing the spatial correlation of wall pressure fluctuations, offering a new perspective on controlling flow-induced vibrations.

Dynamics of constant temperature anemometers for the Martian Atmosphere

The objective of this paper is to understand the limits on the response time generated by the thermal dynamics of the Martian wind sensor of the MEDA instrument, working under Constant Temperature Operation (CTO). This technology has been flown aboard the Mars Science Laboratory, InSight, and Mars 2020. It will be shown that active control thermal anemometry enables a time response to wind fluctuations faster than the time constants defined by the thermal inertia of the sensor components. It will also be shown that the temperature redistributions on the temperature-uncontrolled parts of the supporting structure impose a limit on the bandwidth of the sensor. We present a model of the MEDA hot film anemometers describing what parameters control their dynamical response, why wind tunnel testing confirmed them to be faster than 1 s, and criteria to select materials that reduce the response time to approach 0.2 s.

Enhanced Analysis of Ice Accretion on Rotating Blades of Horizontal-Axis Wind Turbines Using Advanced 3D Scanning Technology

This study investigated the meteorological conditions leading to ice formation on wind turbines in a coastal mountainous area. An enhanced ice formation similarity criterion was developed for the experimental design, utilizing a scaled-down model of a 1.5 MW horizontal-axis wind turbine in icing wind tunnel tests. Three-dimensional ice shapes on the rotating blades were obtained and scanned using advanced 3D laser measurement technology. Post-processing of the scanned data facilitated the construction of solid models of the ice-covered blades. This study analyzed the maximum ice thickness, ice-covered area, and dimensionless parameters such as the maximum dimensionless ice thickness and dimensionless ice-covered area along the blade. Under the experimental conditions, the maximum ice thickness reached 0.5102 m, and the ice-covered area extended up to 0.5549 m2. The dimensionless maximum ice thickness and dimensionless ice-covered area consistently increased along the blade direction. Our analysis of 3D ice shape characteristics and the ice volume under different test conditions demonstrated that wind speed and the liquid water content (LWC) are critical factors affecting ice formation on blade surfaces. For a constant tip speed ratio, higher wind speeds and a greater LWC resulted in increased ice volumes on the blade surfaces. Specifically, increasing the wind speed can augment the ice volume by up to 57.2%, while increasing the LWC can enhance the ice volume by up to 149.2% under the experimental conditions selected in this study.

Investigation of vortex-induced vibration of a Π-type bridge girder and its suppression using G-shaped apron combination measure

The Π-type steel-concrete composite girder, a commonly used bridge deck composed of an upper concrete slab and two lower lateral I-side steel girders, often suffers from severe vortex-induced vibrations (VIVs). Herein, the VIV response and triggering mechanism of a Π-type girder are systematically investigated, by adopting 1:50 scale section model wind tunnel tests and flow-field numerical simulations. Afterward, several aerodynamic measures were designed to mitigate the significant VIVs present in the original section, and an effective measure composed of the G-shaped apron and lower central stabilizer plate was found. Numerical simulation results show that the Π-type girder's upper and lower surfaces both exhibit severe vortex shedding, and both contribute significantly to the occurrence of VIVs. Consequently, the aerodynamic measures introduced for the Π-type girder must be able to simultaneously improve the flowing bypassing situation around the upper and lower surfaces of the section, and the G-shaped apron and the lower central stabilizer plate could both accomplish this simultaneously. The results show that the VIV suppression effect of this G-shaped apron combination measure is greatly affected by the height of the G-shaped apron's vertical plate and the height of the lower central stabilizer plate. Only both of them to a certain height, this measure can entirely prevent the Π-type girder from VIVs. After shape optimization, a G-shaped apron combination aerodynamic measure that can eliminate completely the Π-type girder's VIVs at low damping ratios of about 0.5% is proposed, of which the vibration-suppressing effect was verified by wind tunnel testing of 1:20 section model.

Plume and wall temperature impact on the subsonic aft-body flow of a generic space launcher geometry

Experimental and numerical simulation of launcher base flows are crucial for future launcher design. In experiments, exhaust plume simulation is often limited to cold or slightly heated gases. In numerical simulations, multi-species reactive flow is often neglected due to limited resources. The impact of these simplifications on the relevant flow features, compared to real flight scenarios, needs to be characterized in order to enhance the design process. Experimental and numerical investigations were carried out within the framework of the SFB/TRR 40 Collaborative Research Centre to study the impact of plume and wall temperature on the base flow of a generic small-scale launcher configuration. Wind tunnel tests were performed in the Hot Plume Testing Facility (HPTF) at DLR, Cologne, using subsonic ambient flow and pressurized air or hydrogen–oxygen combustion as exhaust gases. The tests were numerically rebuilt using the DLR TAU code employing a scale-resolved IDDES approach, including thermal coupling and detailed chemistry. The paper combines the experimental and numerical findings from the SFB/TRR 40 base flow studies and highlights the most prominent influences on the mean flow field, the pressure field, the dynamic wake flow motion, and the resulting aerodynamic forces on the nozzle. High-frequency pressure measurements, high-speed schlieren recordings, and time-resolved CFD results are evaluated using spectral and modal analysis of the one- and two-dimensional flow field data.