Delta Wing Research Articles

Exploring the boundary layer transition of hypersonic flow over a compound delta wing

The boundary layer transition on a compound delta wing for Mach 6 has been studied experimentally and numerically. The experiment was performed at Peking University quiet wind tunnel using the Rayleigh scattering flow visualization and infrared thermography. Direct numerical simulations, under the same flow conditions, are applied to analyze the transition mechanism. The results show that the traveling cross flow vortices first appear near the leading edge of compound delta wing. These vortices modulate the mean profile of the flow due to which a rope-like structure appear in the streamwise direction, which is typical of Mack's second-mode. As Mack's second-mode grows to a sufficiently large amplitude, it triggers secondary instability, which behaves as secondary finger like structures. At the end of the transition process, low-frequency waves are excited by Mack's second-mode through an interaction mechanism with their phase speed approaching each other. It is also found that increasing the unit Reynolds number greatly promotes the aerodynamic heating as well as local hot streaks appear on both sides of the compound delta wing in the streamwise direction. The appearance of hot streaks on the compound delta wing is strongly correlated with Mack's second-mode.

Introduction of a biomimetic device designed to improve the flow over a slender delta wing: visualization study

Introduction of a biomimetic device designed to improve the flow over a slender delta wing: visualization study

Boundary layer transition of hypersonic flow over a delta wing

Cross-flow transition over a delta wing is systematically studied in a Mach 6.5 hypersonic wind tunnel, employing the Rayleigh scattering flow visualisation, high-speed schlieren and fast-response pressure sensors. Direct numerical simulations and analysis based on linear stability theory under the same flow conditions are applied to analyse the transition mechanism. Three unstable modes are identified: the travelling cross-flow instabilities, the second mode and the low-frequency waves. It is shown that the travelling cross-flow vortices first appear in the cross-flow region near the leading edge of the model. These vortices can modulate the mean profile of the flow, which benefits the growth of second mode. A phase-locked interaction mechanism transfers energy from the cross-flow instabilities to the high-frequency second mode, leading to amplification at the expense of the cross-flow instability. As the second mode grows to a critical amplitude, it triggers a $z$ -type secondary instability within a similar frequency range, which introduces secondary finger-like structures connecting to the cross-flow vortex. It is further found that the generation of these finger-like structures is related to the expansion and compression of the second mode. These finger vortices further evolve along the streamwise direction into low-frequency waves and corresponding hairpin-like structures that finally trigger turbulence. An interaction mechanism likely exists between the secondary instability and the low-frequency waves, since their phase speeds are approaching each other. These observations of the interaction mechanism are consistent with those of previous studies on hypersonic boundary layers (Zhang et al., Phys. Fluids, vol. 32 (7), 2020, 071702; Li et al., Phys. Fluids, vol. 32 (5), 2020, 051701).

Numerical study of flow and heat transfer in the channel of panel-type radiator with semi-detached inclined trapezoidal wing vortex generators

Abstract To improve heat dissipation performance of panel-type radiator for transformer, this study investigated the flow and heat transfer characteristics of semi-detached inclined trapezoidal wing vortex generator (SDITW) in a closed channel on the air-side of the radiator. The SDITW was compared with the inclined delta wing (IDW) and inclined trapezoidal wing (ITW) channels. The effects of SDITW relative separation height (e 1/e 2), longitudinal pitch (p l), blockage ratio (e/(0.5H)), and inclination angle (α) were analyzed. First, compared with the IDW and ITW channels, the SDITW channel generates stable corner vortices and produces weaker transverse vortices and lower flow resistance due to the semi-detached structure of the wing. For Re = 5,125–15,375, the overall heat transfer performance (performance evaluation criteria; PEC) of the SDITW channel increases by 0.5–8.9 and 1.7–4.9% as compared with IDW and ITW channels, respectively. Furthermore, for the same e/(0.5H) and α, both the Nusselt number ratio and friction factor ratio of SDITW channel increase as e 1/e 2 and p l decrease. For p l = 70 mm, the SDITW channel exhibits a relatively better overall heat transfer performance. For the same e 1/e 2 and p l, the PEC of SDITW channel is maximum and the overall heat transfer performance is best when e/(0.5H) = 0.3 at Re = 10,250 and α = 30°–60°.

Experimental Study of Reverse Flow Solar Air Heater Having Perforation and Delta Wing on Absorber Plate

fThe traditional solar air heater (SAH) has poor thermal performance due to low heat transfer coefficient. Artificial roughness, flow passage alteration, absorber modification, etc. can enhance it. Thus, an experimental investigation is performed to study the thermohydraulic characteristics of a reverse flow SAH with perforated absorber and delta wing (DW) structure. The present study investigates the effect of attack angle (15°–75°) at constant streamwise pitch (35 mm), transverse pitch (70 mm), height (h), and width (w) of DW 20 mm, under Reynolds number (Re) ranging from 4000 to 20 000. The perforation index (PI = ADW/Aap) for inline and staggered arrangements are 9.52 and 4.76, respectively. The results indicate that the concept of perforated absorber and DW leads to enhanced heat transfer, reduced pressure drops, and enhanced utilization of solar energy. The Nusselt number (Nu), friction factor (f), and thermohydraulic performance enhance about 6.6, 9.4, and 3.06 times, respectively, at attack angle 75o for inline arrangement of DW over the smooth duct. Thermohydraulic performance of reversed‐flow SAH is compared with previously published works, and it highlights that the full‐length inline and staggered arrangement of the DW offers the most significant improvements in heat transfer and friction factor.

Analysis of stall characteristics of the cuspidal waverider at subsonic conditions

The stall characteristics of the cuspidal waverider under subsonic conditions were studied at M = 0.4 and H = 0 km incoming flow. The stall characteristics were compared with those of delta wing models with the same leading-edge swept angle and the same aspect ratio. It can be found that the flow field changes of the cuspidal waverider are similar to those of Model 1 and Model 2. The critical angle of attack of the cuspidal waverider is more influenced by the aspect ratio, but less related to the leading-edge swept angle. The lift change of the cuspidal waverider is closely related to the vortex structure on the leeward side. As the angle of attack increases, the vortex structure becomes thicker and stronger, and moves toward the middle of the model under the action of the overflowing high pressure gas on the lower surface. Under the same angle of attack, the vortex structure under the effect of the adverse pressure gradient, the intensity along the flow direction decreases while the vortex continues to move away from the wall. Besides, the possible splitting of large vortex into smaller ones will be another result of the effect of the inverse pressure gradient. The smaller the overall aspect ratio of the model, the greater actual swept angle and the greater effective swept angel of the vortex structure, which allows the vortex to exist at higher angles of attack. When the vortex structure is broken to form a larger recirculation area in the leeward area, the negative pressure at the leeward surface decreases, the lift coefficient decreases, and a stall occurs.

Vortical Structures over a Generic Tailless Chined Forebody–Delta Wing

The flowfield over a model having a chined forebody and a simple delta wing was investigated experimentally using oil flow visualizations and stereoscopic particle image velocimetry at a mean chord-based Reynolds number of 2.3×105, angles of attack of 20 and 30 deg, and yaw angles of 0 and 5 deg. The flowfield over the model exhibited pairs of leading-edge vortices similar to those around a double-delta wing, except for the influence of the fuselage, where the chine vortex followed the curvature. The development and interaction of the two vortices were measured and analyzed. It was found that increasing the angle of attack resulted in wakelike vortices, whereas increasing the yaw angle yielded a wakelike vortex on the windward side and a jetlike vortex on the leeward side. The interaction of the windward side vortex with the physical barrier of the forebody surface was observed to greatly affect its behavior and the interaction downstream. In some configurations, the merged vortex exhibited a breakdown. The flowfield and the vortex dynamics under various conditions are discussed in detail to provide insight into manipulating the flowfield using physics-based flow control.

An Experimental and Numerical Thermal Flow Analysis in a Solar Air Collector with Different Delta Wing Height Ratios

An Experimental and Numerical Thermal Flow Analysis in a Solar Air Collector with Different Delta Wing Height Ratios

О построении оптимальной аэродинамической формы типа «летающее крыло»

Using the method of local variations, the process of constructing the aerodynamic configuration, based on optimizing its shape according to the aerodynamic quality criterion K, is considered. The shape of a delta wing with dimensionless length L ≡ 1 and span b = 1 was taken as the initial configuration in the optimization calculation. The shape and dimensions of internal geometric constraints are taken as the initial data. The volume of the body under study is not fixed. The optimal configuration that realizes the maximum aerodynamic quality has been determined; its properties have been studied. In the additionnal calculation, a prototype geometrically similar to the X 34 project, including the plan form and dimensions of the power plant, was taken as the initial data. The shape of the fuselage and the wing setting angle providing the maximum aerodynamic quality have been determined. An assessment of the aerodynamic quality of the resulting optimal shape shows its compliance with the required conditions.

Effect of Sweptback Angle of a Delta Wing on Surface Pressure Distribution at Supersonic Mach Numbers

Effect of Sweptback Angle of a Delta Wing on Surface Pressure Distribution at Supersonic Mach Numbers

Analysis of Vortex Dominated Flow over Double Delta Wing

The maneuverability of fighter aircraft designed using double delta wing configuration at low subsonic speed in addition to under high angle of attacks are highly appealing and fascinating to comprehend. Flow pattern formed by double delta wing help to facilitate lifting force under high angle of attack and at such low subsonic speed. In comparison to delta wing, vortex formations by strake part of wing play an important role to create a persistent vortex core capable of delaying stalling. In this investigation, force coefficients of 75°/45° double delta wing configuration is extracted both from wing tunnel experiment and numerical calculation between 0° to 30° angles of attack at Reynolds number of 1.4 × 105 based on root chord length. It has also been attempted to investigate the flow pattern formation over wing leeward surface, interaction between vortices formed by strake/wing based on Q-criterion and pressure distribution along propagation path of vortices obtained from CFD (Computational Fluid Dynamics) calculations. Implications of interplay between vortices and pressure distribution in lift generation have also been analyzed. It has been found that around 15° angle of attack strake and wing vortices merge and gets more intensified. With higher angle of attack the lift generation significantly diminishes because of vortex bursting

Fluctuating aerodynamic noise radiated from longitudinal vortex in the flow field with turbulence

The paper focuses on fluctuating aerodynamic noise of automobiles, that is, time-varying wind noise which can significantly affect driver annoyance during at high cruising speed, independent of average loudness. One of the main aerodynamic noise sources is considered as longitudinal vortex behind the front pillar of a vehicle located near driver's ear. The mechanism of fluctuating aerodynamic noise was investigated from quantitative and qualitative viewpoints. Firstly, regarding quantitative noise level, wind-tunnel experiments and numerical simulations have been conducted for the longitudinal vortex around the delta wing subjected to the wake of a circular cylinder. The both results showed that the aerodynamic noise increases around the vortex-shedding frequency by 10 to 20 dB. Numerical analysis investigated the effect of the flow with turbulence on the generation of aerodynamic noise. Karman vortex emitted from the cylinder induces Aeolian tone with 58 Hz. The analysis revealed the noise sources with respect to time derivatives of both vorticity and surface pressure fluctuations, which lead to the increase in noise level around 58 Hz. Secondly, concerning noise quality, modulation spectrum analysis also clarified that the vortex-shedding frequency 58 Hz shifts to the lower frequency 10 Hz, which is considered as the fluctuating aerodynamic noise.

Passive Poststall Flow Control on Nonslender Delta Wings Using Flags

The lift force on two nonslender delta wings with sweep angles of Λ=40 and 50°, with flags attached to the leading edge, was investigated. Substantial lift enhancement in the poststall regime of the clean wings and the stall delay were observed. With a flag, the flowfield measurements showed the reattachment of the shear layer onto the wing surface and the re-formation of the leading-edge vortex, whereas the clean wing had completely stalled flow at the same angle of attack. Over a wide range of angles of attack, mass ratios, and flag lengths, the maximum lift enhancement was attained when the dimensionless frequency of flag oscillations was in an optimal range and the flag-tip velocity had sufficient amplitude. The optimal dimensionless frequency range corresponded to the natural shear layer instabilities of the clean wing. The excitation in this range substantially increased the coherency of the separated flow due to the flag oscillations. The main mechanism of the lift increase is the excitation of the shear layer, which exhibits convective instability. This is very different from the lift enhancement mechanism on airfoils where the flags lock-in to the wake instability, which is known to have an absolute instability at the poststall angles of attack of the clean airfoil.

Numerical investigation for subsonic performance of the high-pressure capturing wing configuration with wing dihedral

High-pressure capturing wing (HCW) aerodynamic configuration demonstrates favorable aerodynamic performance under hypersonic conditions, and its novel additional lifting wing (also known as HCW) has the potential to enhance lift characteristics under subsonic conditions. Therefore, this configuration presents a promising option for wide-speed-range vehicles. However, the stability characteristics of this novel configuration under subsonic conditions have not yet been investigated. In this paper, the effects of wing dihedral angles on the subsonic aerodynamic characteristics of a parametric conceptual HCW configuration with two lifting wings were investigated. Specifically, the design variables for this study were the dihedral angles of the upper HCW and the lower delta wing. To obtain the distributions of various aerodynamic parameters over the design space, a combination of the uniform experimental design method, computational fluid dynamics numerical simulation techniques, and kriging surrogate model algorithm was employed. The findings suggest that wing dihedral angles have a greater impact on the lift-drag ratio (L/D) at low angles of attack compared to high angles of attack. L/D can be enhanced by incorporating a positive dihedral angle in HCW, and as the delta wing's negative dihedral angle rises, L/D tends to increase earlier and decrease later at low angles of attack. Furthermore, for the longitudinal, lateral, and directional stability characteristics of this configuration, the positive dihedral angles of the delta wing offer greater overall advantages than negative ones in improving them, and the positive dihedral angles of HCW yield more significant enhancements in stability compared to negative ones.

Leading-Edge Vortex Controller (LEVCON) Influence on the Aerodynamic Characteristics of a Modern Fighter Jet

The purpose of this paper is to assess the influence of a novel type of vortex creation device called the leading-edge vortex controller (LEVCON) on the aerodynamic characteristics of a fighter jet. LEVCON has become a trending term in modern military aircraft in recent years and is a continuation of an existing and widely used aerodynamic solution called the leading-edge root extension (LERX). LEVCON is designed to operate on the same principles as LERX, but its aim is to generate lift-augmenting vortices, i.e., vortex lift, at higher angles of attack than LERX. To demonstrate the methodology, a custom delta wing fighter aircraft is introduced, and details about its aerodynamic configuration are provided. The LEVCON geometry is designed and then incorporated into an existing three-dimensional (3D) model of the aircraft in question. The research is conducted using OpenFOAM 8, a high-fidelity computational fluid dynamics (CFD) open-source software. The computational cases are designed to simulate the aircraft’s flight at stall velocities within a high range of angles of attack. The results are assessed and discussed in terms of aerodynamic characteristics. A conclusion is drawn from the analysis regarding the perceived improvements in fighter jet aerodynamics. The analysis reveals that both lift and critical angle of attack can be manipulated positively. With the addition of LEVCON, the average lift gain in the high angle of attack (α) range is between 8.5% and 10%, while the peak gain reaches 19.4%. The critical angle of attack has also increased by 2°, and a flatter stall characteristic has been achieved.

Numerical analysis and optimization of the heat transfer enhancement from the heat transfer fluid side in a shell-and-tube latent heat thermal energy storage unit: Application to buildings thermal comfort improvement

This study investigates the impact of enhancing the convective heat transfer on the Heat Transfer Fluid (HTF) side by passive flow manipulation on the melting and solidifying kinetics of a Phase Change Material (PCM) in a shell-and-tube Latent Heat Thermal Energy Storage (LHTES) unit. The PCM used is PureTemp 23 (PT23), a commercial bio-sourced product. The targeted application is the development of a LHTES unit for improving the thermal comfort in buildings through a combined heating and cooling approach. The study is carried out using the commercial code STARCCM+ and the enthalpy-porosity method, with appropriate implementation of the buoyancy source term. The numerical approach used for phase change modeling has been validated by comparisons with reference data from the open literature. Delta Wing pairs (DWg) and Delta Winglet pairs (DWt) vortex generators (VGs), were first inserted into the tube in which the HTF flows. Parametric analysis on the aspect ratio, position, and VGs number were performed, and optimization was done on the attack and rolling angles. The Performance Evaluation Criteria (PEC) index, which takes into account the heat transfer enhancement achieved and the related pressure losses, was used as an assessment criterion to evaluate the heat transfer augmentation of the studied enhanced tube with VGs. The results show that maxima can be reached for the different parametric studies carried out. While PEC increases with the attack angle until a maximum beyond which it decreases, it decreases consistently with the rolling angle. Once the enhanced optimal tube equipped with a shell containing the PCM, the results of the detailed study made on the kinetics for charging and discharging period of the enhanced LHTES unit reveal important gain for the storage unit. The heat transfer enhancement achieved result into more than 110 % increase in the PCM's melting/solidifying kinetics in the shell, thanks to an increase in the heat duty exchanged between the HTF and the PCM, leading to a considerable reduction of complete melting/solidification time. It was observed that the enhanced and optimized LHTES unit developed in the present study has a huge potential for improving buildings seasonal thermal comfort.

Occurrence Characteristics of Lead–Zinc Mine and Low-Flying Aeromagnetic Prospecting in a Forested Region of Yichun City

Understanding the characteristics of lead–zinc mine occurrences and mastering effective investigative techniques are paramount in modern ore prospecting. This research focuses on the forested region of Yichun city in China, with a specific emphasis on the strategic mineral resource of a lead–zinc mine. The study examines the distribution patterns of this mineral and employs advanced aeromagnetic exploration methods. Firstly, we analyzed the geological structure and features of the region by leveraging the latest high-precision aeromagnetic data collected using dynamic delta wing technology. This analysis was complemented by an assessment of the geological conditions of the research area, existing lead–zinc deposits, ground magnetic surveys, and verification studies. With the goal of establishing a meaningful correlation between aeromagnetic anomalies and lead–zinc deposits, we employed various potential field conversion techniques, including the reduction to the pole, vertical derivatives, upward continuation, and residual anomaly analysis techniques. Secondly, we investigated the metallogenic sites within this region and provided a comprehensive summary of the metallogenic circumstances and characteristics related to aeromagnetic prospecting. Thirdly, we employed human–computer interaction fitting inversion techniques to predict the potential for lead–zinc mine prospecting in areas exhibiting aeromagnetic anomalies. The study underscores the significance of high-amplitude and large-scale aeromagnetic anomalies in the study area. Furthermore, we examined the interplay between intrusive rocks, strata, and structural elements within the region to identify favorable conditions for lead–zinc mineralization. As a result of our analysis and discussions, a location was predicted where a lead–zinc mine may exist. The research methodology outlined in this article provides valuable insights for future lead–zinc mine exploration efforts in areas characterized by similar geological conditions.

Verification and Validation of the Spalart Allmaras Model with Rotation and Curvature Correction for Incompressible and Compressbile Flows

The Spalart-Allmaras turbulence model is the model which gets the highest technological readiness level in the NASA turbulence model resource home page. The model is widely used to predict external incompressible and compressbile flows. Different corrections to this model incorporating additional physical effects are presented on the same home page. Unfortunately none of these corrections are available in the official OpenFOAM version. Furthermore, no publicly available repository which contains the full set of corrections suggested by Shur et al. [1] to account for curvature and rotation effects was found. In this technical note, the rotation and streamline curvature correction is incorporated into the Spalart-Allmaras model in order to overcome this limitation. The same equations as suggested in Shur et al. [1] are implemented and verified by means of the incompressible flow in a rotating channel, a 2D bump flow in a channel and a channel flow exhibiting a U-turn. Regarding the rotating channel flow and the flow in a U-turn some quantitative differences remain with respect to the results of Shur et al. [1]. For the rotating channel flow, a careful consistency check with respect to the analytical relations leading to the computation of the factor multiplied with the production term was made. No inconsistencies in the implementation where found. Unfortunately the exact reason for the differences between the present results compared to the computations of Shur et al. [1], was not found. The interested readers are encouraged to help to clarify these issues. In the fourth test case it is shown that the model predicts a more correct turbulent viscosity distribution in the transonic flow around a delta wing. Applying the streamline and curvature corrections to the Spalart-Allmaras model predicts an earlier vortex breakdown compared to the standard Spalart-Allmaras model for a high angle of attack configuration. The agreement with the reference experiments is much better when using the corrections proposed by Shur et al. [1] to the Spalart-Allmaras compared to the standard Splart-Allmaras model.

Numerical study on hypersonic aerodynamic characteristics of the high-pressure capturing wing configuration with wing dihedral

High-pressure capturing wing (HCW) configuration is a potential hypersonic aerodynamic configuration that can simultaneously have good lift-drag characteristics with a large volumetric ratio. The effects of wing dihedral angle on the hypersonic aerodynamic characteristics of a conceptual HCW configuration with two lifting wings are investigated in this paper. Specifically, the dihedral angles of two wings, the upper HCW and the conventional delta wing at the bottom of the body, were regarded as the design variables with a given space. Furthermore, the uniform experimental design method, computational fluid dynamics simulation techniques, and kriging surrogate model algorithm were successively utilized to establish the distributions of aerodynamic parameters over the design space. The results indicate that the lift, drag, and lift-to-drag ratio (L/D) have the similar variation trends as the dihedral angles of the two wings change, and are more sensitive to the positive dihedral angle of the delta wing. When the angle of attack is small, the increasing positive dihedral angle significantly reduces L/D, but as the negative dihedral angle increases, L/D will first increase slightly and then decrease slowly. In particular, when the angle of attack is large, the wing dihedral angles have less influence on L/D. For the longitudinal stability, it is mainly affected by the dihedral angles of the delta wing, and the positive dihedral angle can slightly weaken it, while the negative one hardly changes it. The directional stability can be enhanced by the wing dihedral angles, especially the negative angle. The positive dihedral angle can improve the lateral stability, while the negative weaken it. However, when the angle of attack is large, the large positive dihedral angle of the delta wing may lead to a decrease in the lateral stability.

Effect of gurney flaps on a nonslender delta wing during large-amplitude and high-frequency dynamic pitching

The flow control effect of Gurney flaps on 50° swept delta wings during large-amplitude and high-frequency pitching were investigated both experimentally and numerically. Both force and velocity measurements were conducted and compared with the numerical simulation results. The lift hysteresis was found to be significantly affected by the Gurney flaps. It was found that the leading-edge Gurney flap (LG) acts to redistribute the vorticity over the suction surface of the wing during the upstroke process. The formation and development of the leading-edge vortex (LEV) on the suction surface was delayed by the LG, which was accompanied by enhancement of the lift at high angles of attack. The lower surface pressure can be altered with the flow velocity being slowed down by the trailing-edge Gurney flap (TG), which improves overall lift performance of the pitching wing at small to moderate angles of attack.