Airframe/propulsion integrated aerodynamic performance evaluation is one of the key technologies for hypersonic development. Hypersonic aircraft has the characteristics of high flatness ratio which ...its internal space is fully limited. If the force measurement balance takes up a lot of space when installed, it will make it difficult to install the engine and develop the wind tunnel test. Regarding the issue above, the force measurement and support integrated device is designed. First, the analysis of strength and modal are carried out to verify the response characteristics of the strength and frequency for the proposed device. Second, the integrated device was statically calibrated. The calibration result showed that the device has good linearity, sensitivity, and inter-channel interference. Finally, the aerodynamic load measurement tests under the Ma5.5, Ma6.0, Ma6.5 condition were conducted for a 2 m aircraft model in the <inline-formula> <tex-math notation="LaTeX">\Phi 600 </tex-math></inline-formula> pulse combustion wind tunnel. The maximum measurement error is 6.45%, which is the lift force output result in the Ma5.5. It has good consistency with the existing mature box balance. Therefore, the proposed device can meet the force test requirements of the hypersonic wind tunnel test.
This article presents a new type of multicomponent force measurement system to measure lift force, drag force, and pitching moment in hypersonic wind tunnel, which called the suspension ...force-measuring system (SFMS). The SFMS does not occupy the installation space of the scramjet engine and other key functional components in the air-breathing hypersonic vehicle model. It solves the problem that the conventional aerodynamic force measurement technology occupies too much internal space of the hypersonic vehicle test model and dramatically reduces the design difficulty of scramjet propulsion system in the test model. The SFMS adopts the spatial multi-point distribution support mode for the test model. Therefore, it has an excellent stiffness characteristic, meeting the requirement of support rigidity of wind tunnel force measurements test for large-scale and heavy load test model. Then the designed SFMS is constructed and calibrated. The static calibration results show that each test channel of the SFMS has a good sensitivity of 0.2502 mV/N for drag force test channel, 0.1557 mV/N for lift force test channel, 0.2484 mV/Nm for pitching moment test channel, and the max interference error among the SFMS test channels is less than 2.3%. A series of aerodynamic force experiments have been carried out in the <inline-formula> <tex-math notation="LaTeX">\emptyset 600~mm </tex-math></inline-formula> impulse combustion wind tunnel, and the output data of each test channel well reflected the change process of the total pressure in the test section of wind tunnel. Hence, the proposed device can meet the force test requirements of the hypersonic wind tunnel test.
We have developed a system for remote Raman spectra detection in hypersonic wind tunnel, which can be used in extreme environments such as ultra‐high temperature, high pressure, and complex airflow ...to measure in situ Raman spectra of ceramic matrix composites during oxidation, phase transformation or ablation. The designed system avoids stray light generated by windows and airflow through oblique incidence of excitation light. The time‐resolved method combined with pulsed laser and intensified charge‐coupled device (ICCD) was used to reduce the thermal emission background. An optical structure design based on fiber bundle is adopted to suppress the influence of aero‐optical effects and mechanical vibration on Raman spectrum acquisition. We demonstrated the feasibility of in situ Raman spectra detection in a Mach 5 combustion wind tunnel system. The design of anti‐interference prevents Raman spectra intensity from the influence of wind tunnel testing conditions.
A system for remote Raman spectra detection in hypersonic wind tunnel was developed, which can be used in extreme environments such as ultra‐high temperature, high pressure, and complex airflow to measure in‐situ Raman spectra of ceramic matrix composites during oxidation, phase transformation, or ablation.
In an urban environment, dual vertical axis wind turbines (VAWTs) are expected to demonstrate more advantage than horizontal axis wind turbine. For VAWT, solidity is one of the most important ...characteristics, while it has not been well studied. In this study, to investigate the effect of rotor solidity and other characteristics on the power output of counter-rotating dual VAWTs at different rotor centre spacings in a low turbulence intensity condition, twelve wind tunnel experiments for dual VAWTs and six wind tunnel experiments for an isolated VAWT were conducted. The results show that the effect of the dual VAWTs configuration on the VAWT power output is small compared with isolated VAWT under low wind speeds in an urban environment, but the effect exhibits a slight improvement with an increase in rotor solidity. As rotor solidity decreases, the sensitivity of the effect on rotor centre spacing increases. The effect of skewed flow on the power output of dual VAWTs are also well discussed. Furthermore, dual-VAWT systems are studied under real urban environment of a number of major cities such as Guangzhou, London, and Copenhagen. Potentials in different heights are compared with different configurations based on the city planning of those major cities.
•An experimental test on various dual-rotor system was conducted in a wind tunnel.•The relationship between solidity and the dual rotor system is analyzed.•The performance of the dual rotor system under skewed flow is discussed.•The potential of dual rotor system on building are studied in various major cities.
Blockage effects in wind farms Segalini, Antonio; Dahlberg, Jan‐Åke
Wind energy (Chichester, England),
February 2020, Letnik:
23, Številka:
2
Journal Article
Recenzirano
Odprti dostop
An experimental study of wind farm blockage has been performed to quantify the velocity decrease that the first row of a wind farm experiences due to the presence of the other turbines downstream. ...The general perception has been that turbines downstream of the first row are only influenced by the wakes from upstream turbines without any upstream effect. In the present study, an attempt is made to demonstrate the existence of a two‐way coupling between individual turbines and turbines in the wind farm. Several staggered layouts were tested in the wind tunnel experiments by changing the spacing between rows, spacing between turbines in the rows, and the amount of wind turbines involved. The experiments focused on turbines located in the center of the first row as well as the two turbines located in the row edges, usually believed to experience a speedup. The present results show that no speedup is present and that all the turbines in the first row are subjected to a reduced wind speed. This phenomenon has been considered to be due to “global blockage.” An empirical correlation formula between spacing, number of rows, and velocity decrease is proposed to quantify such effect for the center turbine as well as for the turbines at the edges.
This paper is written as a contribution to the celebration of 50 years of Progress in Aerospace Sciences and of the centenary of the birth of its founder, Dietrich Küchemann. It reviews the evolution ...of the European Transonic Wind Tunnel, ETW, from early conceptual studies to its entry into service and its current capabilities and achievements. It traces the development, from the earliest days, of experimental aerodynamics and of the basic aerodynamic understanding that gave rise to the main periods of wind tunnel building before and after World War II. By about 1960, this activity appeared to have come to a natural halt. The paper gives an account of the role of Küchemann in arguing the need in 1968 for a further step in wind tunnel capability, to provide transonic testing at high Reynolds numbers. It describes his leading role in gaining acceptance of the concept, formulating the specification and promoting studies of alternative, radical design options for the co-operative European project that became ETW. The progress of ETW through design, construction, commissioning and into full operation is recorded. The paper discusses the many technical innovations that have been introduced in order to meet customer requirements in the challenging field of aerodynamic testing in a cryogenic environment and, finally, looks to the future and the further technical challenges that it holds.
This paper investigated the performance of an innovative straight-bladed vertical axis wind turbine (VAWT) with inclined pitch axes (not coincident with the aerodynamic center line of blades). A ...straight blade with an inclined pitch axis used in VAWTs was described and the corresponding VAWT prototype was built and tested in a low speed wind tunnel to validate the feasibility of power output control using the novel design. Effect of blade folding movements on the VAWT performance was illustrated. It is found that the maximum power coefficient is reduced by 62.5% when blades are folded to the fold angle of 2°from the optimal fold angle of 8°. The decrease of the maximum power coefficient is also observed to be 59.0% when blades are folded to the fold angle of 13°. In addition, the control rule of the blade fold angle to maintain constant power output and the folding sensitivity at the rated rotation rate were investigated.
•A novel VAWT with inclined pitch axes is evaluated by wind tunnel experiments.•Maximum power diminishes when blades are folded from the optimal fold angle.•The sensitivity of power output to blade folding movements is related to TSRs.•The fold angle control rule to maintain constant power output is obtained.
The overhead contact line is a tensioned cable structure erected along the railroad to power the electric train. Under the wind load, the galloping of OCL caused by aerodynamic instability may form a ...large amplitude, which is a big potential threat to the normal operation of the electric railway. In this paper, a wind tunnel test is performed to investigate the aerodynamic coefficients of the contact line with two levels of wear. The aerodynamic instability of the contact line can be observed on a worn contact wire at around an 8° wind angle of attack. Employing a nonlinear finite element model of the OCL, the galloping is reproduced and analysed via several numerical simulations. The effect of the wear level and angle of attack on the galloping response is analysed. The galloping amplitude of the contact line spikes at the angle of attack of 8° and 9° at 20% and 30% wear levels, respectively. Then damping dropper is included in the model, and its effect on the suppression of the OCL galloping is quantified. The results indicate that a damping dropper of 100 Ns/m is recommended to be mounted on the railway OCL to reduce the detriment of galloping under a strong wind field.
•The aerodynamics of hyperbolic paraboloids with high and low corners are studied.•Numerical CFD simulations are validated by experimental wind tunnel testing.•Cp-distributions are drafted for ...hyperbolic paraboloid roofs and canopies.•Three important wind orientations are identified.•The influence of the surface curvature on the Cp-distribution is evaluated.
The hyperbolic paraboloid with two high and low corners is the most basic anticlastic double curved shape of tensile surface structures. However, this shape is currently not considered in the existing wind load standards and only very few investigations are documented in literature. Therefore, this study aims to map the mean aerodynamics over hyperbolic paraboloid roofs and extremely thin canopies to help engineers understand the general aerodynamics of these structures. In this study, scaled wind tunnel testing is performed on rigid models of a roof with enclosing walls and a canopy without enclosing walls to draft mean Cp-distributions and standard deviations for various wind orientations. These mean Cp-distributions are validated with the limited studies in literature and used to calibrate and benchmark a numerical wind tunnel, using CFD RANS simulations, that allows to further reduce the thickness of the canopy compared to the wind tunnel models. The numerical wind tunnel is used to study the mean wind load distributions for hyperbolic paraboloid roofs and canopies with different surface curvature for the most important wind orientations. The results in this paper show good agreement between wind tunnel experiments and CFD simulations, with similar variations as established by different studies of the Silsoe cube. First mean Cp-distributions obtained with scaled wind tunnel testing are presented for hyperbolic paraboloid canopies of only 5 mm thick, with similar mean net Cp and only slightly larger suction over the upper and lower face compared to the numerical results for a zero-thickness canopy. The numerical study of different surface curvatures indicates different geometrical patterns in the mean Cp-distributions when the flow starts to separate for highly curved hypars. In general, suction and pressure increase for higher surface curvature, with similar geometrical patterns in the mean Cp-distributions, as long as the flow remains attached. If the flow separates for highly curved hypars, the geometrical pattern differs and the mean Cp drops due to the different behavior of the flow. Finally, the presented mean Cp-distributions give insight in the aerodynamics of hypar roofs and canopies with different surface curvature and could form a basis for future analysis towards peak loads for the design of these structures.
Improving city breathability has been confirmed as one feasible measure to improve pollutant dilution in the urban canopy layer (UCL). Building height variability enhances vertical mixing, but its ...impacts remain not completely explored. Therefore, both wind tunnel experiments and computational fluid dynamic (CFD) simulations are used to investigate the effect of building height variations (six height standard deviations σH = 0%–77.8%) associated to building packing densities namely λp/λf = 0.25/0.375 (medium-density) and 0.44/0.67 (compact) on city breathability. Two bulk variables (i.e. the in-canopy velocity (UC) and exchange velocity (UE)) are adopted to quantify the horizontal and vertical city breathability respectively, which are normalized by the reference velocity (Uref) in the free flow, typically set at z = 2.5H0 where H0 is the mean building height.
Both flow quantities and city breathability experience a flow adjustment process, then reach a balance. The adjustment distance is at least three times longer than four rows documented in previous literature. The medium-density arrays experience much larger UC and UE than the compact ones. UE is found mainly induced by vertical turbulent fluxes, instead of vertical mean flows. In height-variation cases, taller buildings experience larger drag force and city breathability than lower buildings and those in uniform-height cases. For medium-density and compact models with uniform height, the balanced UC/Uref are 0.124 and 0.105 respectively, moreover the balanced UE/Uref are 0.0078 and 0.0065. In contrast, the average UC/Uref in height-variation cases are larger (115.3%–139.5% and 125.7%–141.9% of uniform-height cases) but UE/Uref are smaller (74.4%–79.5% and 61.5%–86.2% of uniform-height cases) for medium-density and compact models.
•City breathability is assessed by in-canopy velocity (UC) and exchange velocity (UE).•Six building height variations withλp/λf = 0.25/0.375 and 0.44/0.67 are studied.•Flow adjustment distance is much longer than the literature (more than 10 units).•Urban model with λp/λf = 0.25/0.375 produces larger UC and UE than λp/λf = 0.44/0.67.•Taller buildings attain better ventilation but lower ones obtain smaller UC -UE.
