Leading Edge Corner Research Articles

Effect of synthetic jets actuator parameters on deep reinforcement learning-based flow control performance in a square cylinder

We conduct an active flow control study on the mass flow rate of synthetic jets on the upper and lower surfaces of a square cylinder using a deep reinforcement learning algorithm, with a focus on investigating the influence of the position and width of the synthetic jets on the flow control performance. At Reynolds numbers (Re) of 100 and 500, it is found that our proposed method significantly reduced the lift and drag coefficients of the square cylinder and completely suppressed vortex shedding in the wake. In particular, at Re = 100, placing the synthetic jets near the tail corner was beneficial for reducing drag, with a maximum drag reduction rate of 14.4%. When Re = 500, positioning the synthetic jets near the leading edge corner resulted in a maximum optimal drag reduction effect of 65.5%. This indicates that locating the synthetic jet at the main flow separation point can achieve optimal control. Furthermore, we notice that when the synthetic jets are positioned near the tail corner, vortex shedding can be completely suppressed. Additionally, a narrower width of the synthetic jets can enhance flow instability and increase the cost of flow control.

Experimental Investigations of Hydrokinetic Turbine Providing Fillet at the Leading Edge Corner of the Runner Blades

Water streams with low heads can be found in India, both naturally as well as through irrigation canals. These natural resources can be used to generate electricity by utilising Hydrokinetic water turbines. The current investigation includes an experimental investigation of the axial flow turbine in order to make use of these naturally available resources. For Axial Flow Turbines (AFT), the influence of the fillet radius at the leading edge corner of the runner blade is studied. The experiments are carried out under various turbine loads and corresponding head conditions. The 3D printed runners with six different fillet radius (Rtu), i.e. 0 mm, 2 mm, 4 mm, 6 mm, 8 mm, and 10 mm are examined experimentally. The results are presented in the form of obtained efficiency (η ) with a diverse Fillet Radius Ratio (FRR) for different Tip Speed Ratio (TSR) and equivalent head (H). The results indicate that, at the head, 0.012 m, with a sharp edge, i.e., FRR = 0 (Rtu = 0 mm), the minimum efficiency of 34.90% is recorded. However, at the same water head, the maximum efficiency of 84.82% is achieved with FRR = 0.046 (Rtu = 2 mm).

Numerical Predictions of Turbine Cascade Secondary Flows and Heat Transfer With Inflow Turbulence

Abstract Turbine passage secondary flows are studied for a large rounded leading edge airfoil geometry considered in the experimental investigation of Varty et al. (“Vane Suction Surface Heat Transfer in Regions of Secondary Flows: The Influence of Turbulence Level, Reynolds Number, and the Endwall Boundary Condition,” ASME J. Turbomach., 140(2), p. 021010) using high resolution large eddy simulation. The complex nature of secondary flow formation and evolution are affected by the approach boundary layer characteristics, components of pressure gradients tangent and normal to the passage flow, surface curvature, and inflow turbulence. This paper presents a detailed description of the secondary flows and heat transfer in a linear vane cascade at exit chord Reynolds number of 5 × 105 at low and high inflow turbulence. Initial flow turning at the leading edge of the inlet boundary layer leads to a pair of counter-rotating flow circulation in each half of the cross plane that drives the evolution of the pressure side and suction side of the near-wall vortices such as the horseshoe and leading edge corner vortex. The passage vortex for the current large leading edge vane is formed by the amplification of the initially formed circulation closer to the pressure side (PPC) which strengthens and merges with other vortex systems while moving towards the suction side. The predicted suction surface heat transfer shows good agreement with the measurements and properly captures the augmented heat transfer due to the formation and lateral spreading of the secondary flows towards the vane midspan downstream of the vane passage. Effects of various components of the secondary flows on the endwall and vane heat transfer are discussed in detail.

Numerical experiments in separating and reattaching flows

We report high-order implicit large Eddy simulations of flows around flat plates with massive flow separation and reattachment. The aim is to provide evidence of the influence of relevant flow parameters such as the geometry of the leading-edge corner, the presence of a trailing-edge flow separation, and of a flow coupling between the two sides of the plate. The results reveal that flows with right-angled corners develop taller flow recirculations, which promote very-slow instability of the bubble itself. This large-scale unsteadiness is then found to be the basis of negative turbulence production mechanisms that in turn enhance the height of the bubble itself, thus closing a self-sustained cycle. The absence of these phenomena in flows with smooth leading-edge corners is also found to explain their high sensitivity to free-stream turbulence. The observed behaviors may have strong repercussions for theories and closures of separating and reattaching flows and should be carefully taken into account in control strategies used in the applications.

Comparative Study of Forward Wingtip Fence and Rearward Wingtip Fence on Wing Airfoil Eppler E562

The perfect wing is a dream that many airplanes has manufactured have been striving to achieve since the beginning of the airplane design. There are some aspect that most influence in aircraft design lift, drag, thrust, and weight. The combination of these aspects leads to a decrease in fuel consumption, which reduces pollution in our atmosphere and increase in economic revenue. One way to improve aircraft performance is to modify the tip of the wing geometry, which has become a common sight on today’s airplanes. With computational programs, the effects on drag due to wingtip devices can be previewed. This research was done numerically by using turbulence model k-ω SST. Reynolds number in this research was 2,34 x 10 4 with angle of attacks are 0o, 2o, 4o, 6o, 8o, 10o, 12o, 15o, 17o and 19o. The model specimen is wing airfoil Eppler 562 with winglets. Two types of wingtips are used: forward and rearward wingtip fence. From this study, it was found that wingtip fence reduced the strength of vorticity magnitude on the x axis compared to plain wings. The leakage of fluid flow effect at the leading edge corner of the wingtip, giving pressure gradient and slightly shifting towards the trailing edge. this occurs in the plain wing and rearward wingtip fence but does not occur in the forward wingtip fence..

Influence of Blade Leading-Edge Shape on Cavitation in a Centrifugal Pump Impeller

Cavitation is an important issue in pumps and usually starts on the blade leading-edge. For fixed blades with constant rotational speeds and specific flow rates, the incident angle, which is between the flow direction and the blade installing direction, on the blade leading-edge plays the key role in the cavitation process. The leading-edge shape is crucial on the local flow separation, pressure distribution, and cavitation. Hence, the influence of the leading-edge shape on cavitation has been studied in the current work in a centrifugal pump impeller. The blunt, sharp, ellipse and round leading-edge cases were compared using numerical simulation and verified by experimental data. Results show different features of cavitation. The round and ellipse leading-edge impellers have higher inception cavitation coefficient. It was caused by the sudden pressure drop on leading-edge arc or elliptical arc. The sharp and blunt leading-edge impellers have a wide flow-separation region on leading-edge with a wide low-pressure region. This is because of the sudden turn in geometry on the leading-edge corner. Cavitation grew quickly after inception and caused rapid head-drop in the sharp and blunt leading-edge impellers. Results suggest the critical cavitation performance is dominated by the leading-edge low-pressure area while the inception cavitation is mostly affected by the minimum pressure value on the leading-edge. The critical cavitation performance can be evaluated by checking the leading-edge low-pressure area. The inception cavitation can be evaluated by checking the minimum pressure value on the leading-edge. These strategies can be used in the further leading-edge designs.

Effective transition of steady flow over a square leading-edge plate

AbstractPrevious experimental studies have shown that the steady recirculation bubble that forms as the flow separates at the leading-edge corner of a long plate, becomes unsteady at relatively low Reynolds numbers of only a few hundreds. The reattaching shear layer irregularly releases two-dimensional vortices, which quickly undergo three-dimensional transition. Similar to the flow over a backward-facing step, this flow is globally stable at such Reynolds numbers, with transition to a steady three-dimensional flow as the first global instability to occur as the Reynolds number is increased to 393. Hence, it appears that the observed flow behaviour is governed by transient growth of optimal two-dimensional transiently growing perturbations (constructed from damped global modes) rather than a single three-dimensional unstable global mode. This paper quantifies the details of the transient growth of two- and three-dimensional optimal perturbations, and compares the predictions to other related cases examined recently. The optimal perturbation modes are shown to be highly concentrated in amplitude in the vicinity of the leading-edge corners and evolve to take the local shape of a Kelvin–Helmholtz shear-layer instability further downstream. However, the dominant mode reaches a maximum amplitude downstream of the position of the reattachment point of the shear layer. The maximum energy growth increases at 2.5 decades for each increment in Reynolds number of 100. Maximum energy growth of the optimal perturbation mode at a Reynolds number of 350 is greater than $1{0}^{4} $, which is typically an upper limit of the Reynolds number range over which it is possible to observe steady flow experimentally. While transient growth analysis concentrates on the evolution of wavepackets rather than continuous forcing, this appears consistent with longitudinal turbulence levels of up to 1 % for some water tunnels, and the fact that the optimal mode is highly concentrated close to the leading-edge corner so that an instantaneous projection of a perturbation field from a noisy inflow onto the optimal mode can be significant. Indeed, direct simulations with inflow noise reveal that a root-mean-square noise level of just 0.1 % is sufficient to trigger some unsteadiness at $\mathit{Re}= 350$, while a 0.5 % level results in sustained shedding. Three-dimensional optimal perturbation mode analysis was also performed showing that at $\mathit{Re}= 350$, the optimal mode has a spanwise wavelength of 11.7 plate thicknesses and is amplified 20 % more than the two-dimensional optimal disturbance. The evolved three-dimensional mode shows strong streamwise vortical structures aligned at a shallow angle to the plate top surface.

Effects of incidence angle on endwall convective transport within a high-turning turbine rotor passage

Effects of incidence angle on the endwall convective transport within a high-turning turbine rotor passage have been investigated. Surface flow visualizations and heat/mass transfer measurements at off-design conditions are carried out at a fixed inlet Reynolds number of 2.78 × 10 5 for the incidence angles of −10°, −5°, 0, 5°, and 10°. The result shows that the incidence angle has considerable influences on the endwall local transport phenomena and on the behaviors of various endwall vortices. In the negative incidence case, convective transport is less influenced by the leading edge horseshoe vortex and by the suction-side corner vortex along their loci but is increased along the pressure-side corner vortex. In the case of positive incidence, however, convective transport is augmented remarkably along the leading edge horseshoe vortex, and is much influenced by the suction-side corner vortex. Moreover, heat/mass transfer is enhanced significantly along the pressure-side leading edge corner vortex. Local endwall convective transport in the area other than the endwall vortex sites is influenced significantly by the cascade inlet-to-exit velocity ratio which depends strongly on the incidence angle.

Effects of the corner radius on the near wake of a square prism

The near wake of square cylinders with different corner radii was experimentally studied based on particle imaging velocimetry (PIV), laser doppler anemometry (LDA) and hotwire measurements. Four bluff bodies, i.e., r/d=0 (square cylinder), 0.157, 0.236, 0.5 (circular cylinder), where r is corner radius and d is the characteristic dimension of the bluff bodies, were examined. A conditional sampling technique was developed to obtain the phase-averaged PIV data in order to characterize quantitatively the effect of corner radii on the near-wake flow structure. The results show that, as r/d increases from 0 to 0.5, the maximum strength of shed vortices attenuates, the circulation associated with the vortices decreases progressively by 50%, the Strouhal number, St, increases by about 60%, the convection velocity of the vortices increases along with the widening of the wake width by about 25%, the vortex formation length and the wake closure length almost double in size. Meanwhile, both the vortex wavelength, λ x , and the lateral spacing, λ y , decrease as r/d increases, but the ratio of λ y to λ x is approximately 0.29, irrespective of r/d, which is close to the theoretical value of 0.281 for a stable Karman vortex street. The decrease in wavelength is probably responsible for the change in the flow structure from the approximately circular-shaped vortex at r/d=0 to the laterally stretched vortex at r/d=0.5. The leading edge corner radius is more important than the trailing one in influencing the near wake structure since it determines to a great extent the behavior of the streamlines, the separation angle and the base pressure. It is further found that the ratio of the mean drag coefficient to the total shed circulation, C d/Γ0, approaches a constant, about 0.25 for different bluff bodies in the subcritical flow regime. The streamwise evolution of vortices and the streamwise fluctuating velocity along the centerline for rounded cylinders are also discussed.

Investigation of the structure of turbulent flows in streamwise asymmetric corner configurations

The results of extensive experimental studies of the structure of three-dimensional flow in a region of interaction of asymmetrically developing incompressible turbulent boundary layers by a longitudinal flow around corner configurations are presented. The character of the originating secondary flows is analysed depending on the degree of the flow asymmetry and on the geometry of the leading edge corner. The mechanisms of origin, subsequent development and transformation of secondary flows along the length of a model are discussed. In particular, it is shown that a one-vortex scheme of the flow gradually transforms into a two-vortical one with increasing distance from the leading edge corner.