Short takeoff and landing (STOL) aircraft are an important part of life in Alaska. These aircraft allow pilots to land in places that would otherwise be considered too small for a standard aircraft. Part of being a STOL capable aircraft requires slow speed flight at high angles of attack. Many of the true STOL aircraft in Alaska are modified commercially available aircraft that were never designed for these high angles of attack. This paper will propose and analyze a set of modifications to an already modified Piper Cub to improve the tail authority at these higher angles of attack. These modifications include changing the cross-sectional geometry of the horizontal stabilizer, increasing the area of the tail, and increasing the length of the wing leading edge slats to improve flow quality. CFD was performed on both the original and modified designs in a variety of flight configurations to evaluate the stability and control of the aircraft system at a free stream velocity of 30mph. Analysis of the CFD found that the elevator authority increases by 12.3% and the maximum achievable angle of attack increases by approximately 5.5 degrees.

The prediction of deep-sea mining sediment plumes is essential for assessing and mitigating the environmental impacts on vulnerable deep-sea ecosystems. In this paper, the numerical simulation method is adopted to predict the sediment plume transportation. Fluid dynamics are governed by the incompressible Navier–Stokes equations, coupled with the Standard k–ε turbulence model to capture turbulent diffusion. The air–water free surface is tracked by a high-resolution Volume of Fluid (VOF) method. The pressure–velocity coupling utilizes the PISO algorithm. Sediment transport is governed by the advection–diffusion equation. The mathematical model is validated through experiments. There is a good consistency between the experiment results and the numerical results, which proves that the numerical method can be applied. The study calculates the diffusion range and characteristics of plumes under different free stream velocities, injection velocities and discharge densities. The results indicate that an increase in free stream velocity enhances the development of turbulence, but conversely restricts the expansion of the mixing zone between the plume and the ambient water. A greater injection velocity leads to a wider distribution range of the plume, while inhibiting the development of local turbulence. A higher plume discharge density results in a larger horizontal distribution range, while hindering the effective mixing between the plume and the ambient water body.

Transition onset of high-speed boundary layers can move first downstream and then upstream with increasing nose-tip bluntness, which is called transition reversal. For the first time, our recent research reproduced the experimentally observed transition reversal by direct numerical simulation (DNS, Guo et al. , J. Fluid Mech. vol. 1005, 2025, A5). As a continuation study, this work explores the effect of the form of free-stream disturbances, as the transition in the large-bluntness regime still remains poorly understood. The free-stream Mach number is 5 and the nose-tip radius 3 mm of the blunt plate exceeds the experimental reversal value. Three-dimensional broadband perturbation is carefully constructed through superimposition of planar fundamental waves in the free stream, which initiates the transition in DNS. For each Fourier component, the same perturbation strength is applied for slow/fast acoustic, vortical and entropic waves. All the cases present a ‘streak-turbulent spot’ two-stage transition scenario due to non-modal instabilities. The transition onset locations induced by entropic and slow/fast acoustic waves are close and significantly ahead of that by vortical waves. More evident impact of the disturbance form is manifested in the length of the transitional region, which is the shortest for entropic waves and the longest for vortical waves. Regarding the effect of the angle of incidence that mimics the tunnel environment, it alters the post-shock acoustic-wave structure and reduces the length of the transitional region. In the streaky stage, the form of free-stream disturbances changes the pronounced spanwise wavelengths on the blunt nose and the plate, where the two regions also differ from each other. In the turbulent-spot region, the shortest transitional region induced by the entropic wave is attributed to its largest mean spanwise spreading rate of the turbulent spot. From the perspective of energy budget, shear-induced dissipation dominates the heat transfer escalation in the transitional region. Overall, with significant leading-edge bluntness, the flight environment may tend to result in delayed transition onset compared with the tunnel counterpart.

The merging of two turbulent fronts without mean shear is investigated by direct numerical simulations. The turbulent streams are created by prescribing instantaneous velocity fields from precursor simulations of homogeneous isotropic turbulence (HIT) as inlet conditions for spatially evolving turbulent merging. The fronts are initially separated by a distance $H$ and convected with a uniform free stream velocity $U_{\infty }$ . The inlet turbulence intensity varies in the range of $0.24 \leqslant u^{\prime}/U_{\infty } \leqslant 0.47$ , while the inlet Taylor-scale Reynolds number is in the range of $151 \leqslant \textit{Re}_{\lambda } \leqslant 317$ . As the flow develops in the streamwise direction, two distinct regions are identified: (i) an initial linear decay region, where the two turbulent fronts gradually approach each other without noticeable interaction; and (ii) a rapid decay region, where the opposing turbulent fronts influence one another and eventually merge. The flow statistics collapse once the streamwise coordinate is rescaled as $x^{+} = (x/H) (u^{\prime}/U_{\infty })$ , suggesting that the merging location is imposed by large scales. An analysis conditioned to the developing turbulent/non-turbulent interfaces (TNTIs) reveals that, within the merging region, conditional mean enstrophy profiles deviate from those observed in ‘classical’ TNTIs, indicating a locally more homogenous flow. Within this region of interaction, the surface area of the TNTI increases while the volume of irrotational fluid steadily decreases, resulting in the generation of fine-scale structures. These findings support that turbulent merging is a multiscale process, where both the largest and smallest scales of motion intervene.

Abstract Energy harvesting from vortex-induced vibrations is a promising technology that relies on the vibrations of bluff bodies due to the vortex shedding phenomenon. Increasing the vibration amplitude at a given free stream kinetic energy is therefore equivalent to enhancing the efficiency of the harvesting device. In this study, we assess the potential of alternate slot blowing to amplify force fluctuations. Pressurized air is ejected alternately from the top and bottom parts of a cylinder. Through experimentation in a low-speed wind tunnel (Re = 8,000), we show that the magnitude of lift fluctuations can be enhanced by up to a factor of three compared to the unforced flow when the actuation is aligned with the natural vortex shedding frequency. Particle image velocimetry measurements indicate that this is caused by strong streamline bending, whereas at a higher forcing frequency, the vortex shedding is observed to be suppressed. This work elaborates on the physics of slot blowing for amplitude enhancement, and results suggest that a significant increase in the dynamic load acting on a cylinder can be achieved with carefully chosen active-flow control parameters, thereby promoting future energy harvesting applications.

Abstract Fire testing for civil aircraft is a crucial component of aircraft safety assessment. The flame temperature of the burner directly impacts the accuracy of fire tests. This study focuses on the Sonic burner as the research subject. Using a movable thermocouple rake, the influence of test specimens on the flame temperature field distribution of the Sonic oil burner was investigated. The findings reveal that the closer the Sonic burner is to the conical barrel exit region, the greater the difference between the outer flame layer temperature and the centerline temperature. Furthermore, when a specimen is present, the flame under impingement conditions exhibits smaller vertical cross-section temperature differences in the region near the specimen compared to free stream conditions. As the measurement location approaches the conical barrel exit region, the flame temperature field increasingly resembles that of the free stream state. This research provides fundamental reference data for fire test studies based on the Sonic burner.

The present study describes the flow behavior around the leading edge of a convex wedge having a specific dimension under varying upstream Mach numbers ranging from 1.4 to 2. The interaction between the free stream flow and the wedge significantly affects flow parameters such as static pressure, density, static temperature, downstream Mach number, and shock standoff distance (SSD), which are crucial for efficient aerodynamic design. Previously, various researchers have considered the convex wedge flow configuration specifically for inviscid flow but limited attention has been given to the detailed behavior of flow parameters at the leading edge of a convex wedge under varying upstream Mach numbers. The results indicate that, static pressure increased almost 80% at upstream Mach number 2 at the leading edge of the convex wedge. Density, static temperature, downstream Mach number all of them increased by 40%, 28%, and 40% respectively. The downstream Mach number, at first increases slowly but change takes place rather rapidly when the upstream Mach number crosses the value of 1.6. Again, the SSD showed an abrupt change (almost 95% decrease of its initial value at upstream Mach number 2). The leading edge was chosen for this study since it’s considered to be the critical design point which experiences the highest thermal and aerodynamic loads due to the shockwave. Evaluating flow behavior at this point is crucial in managing shockwave-induced loads.

Abstract Laminar-turbulent transition in boundary layers is important to turbomachinery flows. Accurate prediction of boundary layer state is necessary when calculating entropy generation and heat transfer rates on blades and end walls. Current practice uses a mix of empirical correlations, experimental testing and the experience of the designer to account for transition; however, in complex flows at the decreasing Reynolds numbers found in modern machines, prior knowledge is insufficient. As such, there remains a need for correlations that can be fed into low-order methods for routine use in design. Many such correlations are available; however, the data they are based on is limited, particularly for flows with strong pressure gradients and high free stream turbulence such as those found in turbomachinery. This work consolidates existing literature data for boundary layer transition onset under the influence of free stream turbulence and pressure gradients. Details of the methods used in the original studies are discussed. Data is compared to existing correlations and areas with insufficient data are identified, along with suggestions for future work to fill gaps in the literature.

Abstract The study of nanofluid flows over stretchable wedge geometries has long held significance in fluid mechanics due to its wide‐ranging thermal engineering applications. This work investigates the heat transfer characteristics and flow behavior of a ternary hybrid nanofluid over a stretchable wedge under forced convection, considering both low and high nanoparticle volume fractions. Here, we use water as a base fluid and copper oxide, titanium dioxide, and silicon dioxide as nanoparticles. Ternary hybrid nanofluids exhibit superior thermal conductivity and heat transfer capabilities compared to conventional base fluids, offering potential benefits in applications such as solar thermal systems, heat exchangers, heat pumps, naval propulsion, air purification systems, automotive cooling, electric chillers, nuclear reactors, turbines, and biomedical devices. The unsteady, incompressible, and two‐dimensional governing equations comprising the continuity, momentum, energy, and species concentration equations are transformed into non‐dimensional form. These equations are solved numerically using the BVP4C shooting method implemented in MATLAB to analyze the influence of key parameters on velocity, temperature, and concentration profiles. Results reveal that increasing the nanoparticle volume fraction decreases the velocity while enhancing the thermal profile. Both heat and mass transfer rates rise with higher nanoparticle loading, but decrease near the free stream. At early stages of flow, heat transfer rates are minimal, yet temperature profiles are significantly elevated due to nanoparticle dispersion. This study provides valuable insights into optimizing thermal performance over stretchable wedge geometries. The findings hold particular relevance for thermal energy storage, moisture control systems, and temperature‐regulated storage applications such as cooling warehouses, garment preservation, and food storage, where enhanced heat transfer efficiency is crucial.

Examining eddy viscosity based LES analyses using low to moderate Reynolds number free stream turbulence due to anisotropic forcing

The Stokes boundary layer (SBL) is the oscillating flow above a flat plate. Its laminar flow becomes linearly unstable at a Reynolds number of $\textit{Re} = U_0 \sqrt {T_0/\nu } \approx 2511$ , where $U_0$ is the amplitude of the oscillation, $T_0$ is the period of oscillation and $\nu$ is the fluid’s kinematic viscosity, but turbulence is observed subcritically for $\textit{Re} \gtrsim 700$ . The state space consists of laminar and turbulent basins of attraction, separated by a saddle point (the ‘edge state’) and its stable manifold (the ‘edge’). This work presents the edge trajectories for the transitional regime of the SBL. Despite linear dynamics disallowing the lift-up mechanism in the laminar SBL, edge trajectories are dominated by coherent structures as in other canonical shear flows: streaks, rolls and waves. Stokes boundary layer structures are inherently periodic, interacting with the oscillating flow in a novel way: streaks form near the plate, migrate upward at a speed $2\sqrt {\pi }$ and dissipate. A streak-roll-wave decomposition reveals a spatiotemporally evolving version of the self-sustaining process (SSP): (i) rolls lift fluid near the plate, generating streaks (via the lift-up mechanism); (ii) streaks can only persist in regions with the same sign of laminar shear as when they were created, defining regions that moves upward at a speed $2 \sqrt {\pi }$ ; (iii) the sign of streak production reverses at a roll stagnation point, destroying the streak and generating waves; (iv) trapped waves reinforce the rolls via Reynolds stresses; (v) mass conservation reinforces the rolls. This periodic SSP highlights the role of flow oscillations in sustaining transitional structures in the SBL, providing an alternative picture to ‘bypass’ transition, which relies on pre-existing free stream turbulence and spanwise vortices.

In this study, flow fields around circular cross-sectioned high-rise structures with and without balconies have been investigated. Three different balcony heights (h/d1=3, h/d1=3.5, h/d1=4) and three different balcony diameters (35 mm, 40 mm, 45 mm) were considered in the study, with the experiments carried out at a free stream velocity of 15 m/s. In the experimental part of the study, flow visualization around the model (h/d1=3.5) was achieved using the smoke-wire technique in the wind tunnel test section. In the numerical part, the flow patterns around the models, velocity distributions, and pressure coefficients on the balcony surfaces are calculated using the Realizable k-ε turbulence model. The pressure coefficient distributions are directly affected by the position of different balcony heights. When different balcony heights are compared, it is seen that the highest pressure coefficient values are achieved for h/d1=3, while the most critical pressure coefficient values are obtained in the case of h/d1=4.

A formal optimization procedure is reported for an external-compression supersonic intake with the twin objectives of maximizing the total pressure recovery while simultaneously minimizing the intake pressure drag. Prior to that, two key design modifications are introduced to the supersonic intake. First, a small cowl offset distance is applied, deliberately violating the shock-on-lip condition. This ensures an attached external shock at the cowl, which is beneficial, in return for a small, controlled flow spillage. Second, in a novel development, an internal wedge angle is introduced at the cowl lip, which forces the terminal shock to be a strong oblique shock. This also helps anchor the terminal shock at the cowl lip for a range of intake back-pressure values, and reduces the cowl external angle with respect to the free stream. The optimization problem is formulated based on axiomatic design theory with the two design parameters innovatively selected as the Oswatitsch ramp angle triplets and the cowl internal wedge angle, respectively. A multi-objective genetic algorithm (MOGA), assisted by a Kriging meta-model with infilling, is run in tandem with a RANS solver, to iteratively compute the Pareto front. The optimal design yields ramp angles that are somewhat smaller than the theoretical Oswatitsch values, yet returns a total pressure recovery very close to the Oswatitsch optimum while reducing the intake pressure drag significantly.

The characteristics of velocity fields and profiles in the laminar boundary layer of an undular bore propagating on a horizontal bed are experimentally investigated, employing a high speed particle image velocimeter. A suddenly lifted gate installed in a flume was used to produce an undular bore (with a water depth ratio of 1.70). Based on these measured results, the temporal variation of the horizontal pressure gradient in the free stream is delineated to highlight the relationship between the spatiotemporal acceleration/deceleration in the laminar boundary layer and the pattern of the horizontal pressure gradient. In addition, various shapes of velocity profiles (including flow reversal and overshooting) obtained at different instants and locations are classified into eight kinds, along with distinct definitions of the boundary layer thickness as well as the representative length and velocity scales clearly identified. It is found that the boundary layer thickness keeps increasing with increasing time even when the bottom boundary layer is undergoing different patterns of the horizontal pressure gradient. Four similarity profiles with the dimensionless forms of horizontal velocity profiles in the bottom boundary layer are established temporally and spatially under distinct horizontal pressure gradients, together with the counterparts of solitary waves incorporated for comparison. This study provides a unique example that elucidates the related similarity profiles in the boundary layer of the unsteady undular bore with different types of horizontal pressure gradients, including favorable, zero, and adverse ones.

Abstract The complex interaction flow field induced by jet flow and supersonic free stream about large slenderness ratio missile including compound trajectory jet and rear rudder is numerically studied. Two types of cold jet flow parameters conversion method is researched by RANS. The detailed multiple jet interaction flow field and aerodynamic results are compared with binary hot jet flow. The research results show that several kinds of shock wave, vortex structures are generated due to interaction of multiple lateral trajectory jet flow with rudder. The jet flow affects the pressure distribution in the downstream area. There are obvious differences between two types of cold jet flow parameters. Consistent mass flow ratio conversion simulation result, named as cold 1 is more close to the simulation result of hot jet flow when compared with total temperature of 293.15K conversion simulation result, named as cold 2.

ABSTRACT This piece of work provides an in‐depth analysis of magnetohydrodynamics (MHD) fluid flow and heat transport near a continuously moving vertical plate in the presence of nonlinear thermal radiation with convective boundary condition. A nonlinear dependence of thermal radiation on temperature enhances thermal transport, while convective boundary conditions govern heat transfer at the plate surface. The governing partial differential equations (PDEs) are transformed into ordinary differential equations (ODEs) through the application of a similarity transformation. To numerically solve these ODEs, we have used bvp4c method in MATLAB. The influences of dimensionless parameters on heat transfer and fluid flow are presented using tables and graphs. The key novelty of this study lies in analyzing the impact of nonlinear thermal radiation on MHD flow over a constantly moving vertical plate using the bvp4c method. When the fluid flows in the positive x‐direction and the plate moves in the opposite direction, the coefficient of skin friction decreases. Moreover, when the direction of the fluid and the plate is the same, both the velocity and the temperature profiles increase with greater nonlinear thermal radiation. Near the wall, the temperature gradient decreases as nonlinear thermal radiation intensifies, while it increases in the free stream. The thickness of the thermal boundary layer decreases, while the thickness of the velocity boundary layer increases with increasing magnetic parameter. Similarly, when the Grashof number increases, the velocity boundary layer becomes thicker, while the thermal boundary layer tends to become thinner. However, when the Prandtl number increases, the thermal boundary layer becomes thicker, whereas the velocity boundary layer tends to become thinner. Practically, these findings aid in optimizing heat transfer in engineering applications such as cooling systems, heat exchangers, aerospace thermal protection, and biomedical devices.

We develop an optimal resolvent-based estimator and controller to predict and attenuate unsteady vortex-shedding fluctuations in the laminar wake of a NACA 0012 airfoil at an angle of attack of 6.5°, chord-based Reynolds number of 5000 and Mach number of 0.3. The resolvent-based estimation and control framework offers several advantages over standard methods. Under equivalent assumptions, the resolvent-based estimator and controller reproduce the Kalman filter and LQG controller, respectively, but at substantially lower computational cost using either an operator-based or data-driven implementation. Unlike these methods, the resolvent-based approach can naturally accommodate forcing terms (nonlinear terms from Navier–Stokes) with coloured-in-time statistics, significantly improving estimation accuracy and control efficacy. Causality is optimally enforced using a Wiener–Hopf formalism. We integrate these tools into a high-performance-computing-ready compressible flow solver and demonstrate their effectiveness for estimating and controlling velocity fluctuations in the wake of the airfoil immersed in clean and noisy free streams, the latter of which prevents the flow from falling into a periodic limit cycle. Using four shear–stress sensors on the surface of the airfoil, the resolvent-based estimator predicts a series of downstream targets with approximately $3\,\%$ and $30\,\%$ error for the clean and noisy free stream conditions, respectively. For the latter case, using four actuators on the airfoil surface, the resolvent-based controller reduces the turbulent kinetic energy in the wake by $98\,\%$ .

Hypersonic transition studies on systems sustaining multimodal dynamics are critical to understanding aerothermal loading on flight-relevant configurations. The present work evaluates transition mechanisms in hypersonic boundary layers over a cone–cylinder–flare geometry, and its sensitivity to free stream disturbance amplitudes, using a global linear stability approach and direct numerical simulations (DNS). Under relatively quiet conditions, the flow field resembles the laminar solution, consisting of a large separation zone over the cylinder–flare junction. Linear analysis identifies multiple convective instabilities including, oblique first modes and two-dimensional second modes over the cone segment, and shear layer instabilities over the separation zone. This separation zone also supports a stationary global instability, producing streamwise streaks with an azimuthal wavenumber, $m=21$ , which eventually drives transition as captured in the DNS. Conversely, at higher disturbance amplitudes, the largely attached boundary layer transitions through a bypass mechanism, involving intermodal interactions between low-frequency streaks, and first mode instabilities. The resulting upstream shift in transition onset leads to a significant rise in both steady and unsteady surface loading. Peak thermal loading under quiet conditions displays the signature of the linear global instability over the flare, whereas that under noisier environments is dominated by an imprint of unsteady Görtler vortices over the cylinder–flare junction.

Abstract This research aims at analysing the particle-laden flow of the high-enthalpy wind tunnel L2K, which is used to characterize the impact of dust particles on the recession behaviour of thermal protection systems during Martian entry flight. In the tests, a slightly simplified Martian atmosphere ( $${\text{97\% CO}}_{{\text{2}}}$$ 97\% CO 2 and $${\text{3\% N}}_{{\text{2}}}$$ 3\% N 2 ) is used. The high-enthalpy flow is loaded with micrometric particles of magnesium oxide. Several samples for stagnation point tests made of P50 cork are positioned inside the particle-laden flow. The particles’ mean velocity is measured at the stagnation point of the probe in a region of interest that includes the free stream and the shock layer, with a 2D-2C particle image velocimetry (PIV) system. Several particle flow features are observed, such as the particle’s steep velocity gradient across the shock, the shock layer, and a counter-flow that might be caused by outgassing and rebounded particles. Average particle velocities ranging from 0 to 2100 m/s are measured and compared with the numerical simulation of the wind tunnel’s particle-free flow. A discussion on particle agglomeration due to melting is reported, and the importance of considering this effect for the simulation of atmospheric entry in particle-laden atmospheres is highlighted. Particles are collected with double-sided copper tape on a cooled probe and analysed with a scanning electron microscope (SEM) and with energy-dispersive X-ray spectroscopy (EDX), to characterize their morphological change during their residence time in the wind tunnel flow. Graphic abstract

The cross section of a bluff body free to undergo flow-induced vibration plays a critical role in its vibration characteristics. The physics behind the driving force changes altogether, depending on the cross-sectional geometry. While the curved surface allows flexible separation points, the sharp-edged geometry has fixed locations of flow separation. The D- and C-section prisms that fall into both categories offer hybrid dynamics depending on their orientations and flow conditions. This motivated us to examine the above-mentioned test specimens, especially the role of the cavity of the C-section prism. We experimentally investigate the flow-induced vibrations and the energy harvesting performance of circular, C-, and D-section prisms (closed and open semi-circular cylinders) in a reduced velocity range of 2–16 and a Reynolds number range of 1500–10 500. We discuss the response of the test specimen using displacement amplitude, fluid forces, and power spectral density of the two. The response of the D- and inverted C-section prism is indistinguishable, suggesting no active role of the cavity when placed as the front body. These configurations show a combined vortex-induced vibration (VIV)—galloping response. However, the inverted D-section prism shows a pure VIV response with no lower branch. A notable finding of this study is that the C-section prism, with the cavity as the afterbody, produces negligible vibration amplitude, thereby mitigating VIV. In addition, the energy harvesting efficiency of all test sections is compared, and the D-section prism is found to be most efficient.