Investigation on the Blade Leading Edge Film Cooling with Normal and Staggered-Oblique Impinging Jets

The Editorial Calendar details upcoming publication plans for The Leading Edge.

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The January issue of TLE is a general submissions issue featuring a diverse collection of technical papers. This file includes the entire issue in PDF format.

前缘涡流发生器对S809翼型气动性能影响的研究

The year 2024 was an objectively great one for The Leading Edge (TLE). Besides the continuation of more-than-respectable journal metrics (see Kyle Spikes' President's Page in this issue), TLE also enjoyed a marked increase in manuscript submissions. With more than two weeks left in 2024 at the time of this writing, submissions were up by more than 30% compared to 2023. As TLE enters its 44th year of continuous publication, we hope to continue this upward trend in 2025 — a year we open with another of our popular “general submissions” issues.

Numerical Investigation of Flow Dynamics and Cooling Performance in Combined Porosity Structures at the Leading Edge of a Hypersonic Vehicle

Abstract A common problem for gas turbine engines after ingesting atmospheric dust is compressor fouling, where small particles adhere to component surfaces. By sampling components from both a test engine and a service engine, deposits that are hard and sintered were observed to have formed on the leading edges of compressor blades and stators reprofiling their leading-edge geometry. Sectioning of the components showed that the deposits consist of layers of different chemical compositions and that new minerals have crystallized within the deposits. The change in geometry caused by the deposits suggests that they negatively affect the operating incidence range, surface pressure distribution, and profile losses from the design intent of the original component, changing the compressor working line and reducing surge margin, efficiency, and pressure ratio.

Abstract This contribution focuses on the validation of a numerical strategy developed jointly by Safran and Polytechnique Montréal for the simulation and the analysis of blade-tip/casing contact interactions in low-pressure compressor stages. A large experimental campaign provided data (including strain measurements on the blade and abradable coating wear profiles) for several contact configurations involving four distinct blades and one type of abradable coating. The numerical strategy is here improved by introducing a new cutoff criterion to ensure the physical relevance of the presented results, specifically by keeping the maximum stress within the blade below the material's yield stress. Similarly to previous publications involving a single contact configuration, the numerical model is first calibrated for one of the four blades of interest. It is seen that the results using the numerical model—critical speed, relative wear depth between leading edge (LE) and trailing edge (TE), and maximum stress levels within the blade—are in good agreement with the experimental observations. Using the same calibration, numerical simulations are then blindly run for the three other blades. The results demonstrate that numerically predicted key quantities align well with experimental data. Additionally, the numerical model provides an accurate relative assessment of a blade's sensitivity to contact in agreement with experimental observations. This paper thus presents the first blind validation of a numerical strategy dedicated to blade-tip/casing contact interactions. Simultaneously, it also demonstrates that this model may be considered for the early discrimination of blade profiles depending on their sensitivity to contact.

The present study provides comprehensive experimental investigations into the use of wavy leading edge (LE) and trailing edge (TE) serrations as a passive means for augmenting the reductions of fan broadband noise. The findings clearly indicate that the wavy LE – TE serrated fan could yield greater noise reduction performance than the un-serrated and wavy LE serrated fan, over a wide range of frequencies. In general, the wavy LE-TE serrated fans offer a maximum noise reduction of about 10 - 6 dB and an average reduction of about 4 - 5 dB, over a broad range of frequencies. For the range of frequencies from about 3 to 8 kHz, the wavy LE – TE serrated fan delivers a notable additional noise reductions of about 1-2 dB as compared to LE serrated ones, which is observed for all rpm values. For all rpm values, the un-serrated and serrated fans exhibit maximum / minimum directivity at an emission angle of about 127.5o / 77.5o. The lower far-field acoustic emissions (i.e., interaction noise + self-noise) offered by the wavy LE-TE serrated fans arises due to intense far-field destructive interference as a result of the faster spanwise phase variation of the velocity/pressure as well as the higher spanwise de-coherence. Further, the wavy LE-TE serrations mitigate direct scattering at both the LE and TE by dispersing sound energy over a wider area, which results in less intense noise signature in the far field. Thus, it clearly demonstrates that the second generation wavy LE-TE serrations could provide the substantial reduction of the far-field noise as compared to first-generation wavy serrations over a broad range of frequencies.

Abstract In desert regions, there is a significant presence of dust and sand particles lifted by storms and drawn into aircraft engines, resulting in considerable erosion. This numerical study investigates the dynamics of sand particles affecting the front components of a high-bypass turbofan engine (HBTFE). The components under consideration include a Pitot intake, a spinner, a fan rotor, inlet guide vanes (IGVs), and outlet guide vanes (OGVs). This research focuses on the engine's operating conditions during takeoff from a Saharan airfield. The flow field is solved separately, and the data are transferred to an in-house particle trajectory code based on the Lagrangian model. The finite element method (FEM) is used to track sand particles as they move through the mesh cells, facilitating an accurate assessment of impacts and conditions necessary for calculating erosion rates. The results obtained indicate that a significant number of sand particles frequently impact the rotor blade, from the hub to approximately 80% of its span, due to deflection by the Pitot intake lip and outer contour. The pressure side (PS) of the rotor blade experiences severe erosion, with the highest erosion rates occurring at the leading edge (LE) and toward the trailing edge (TE). At the exit of the rotor, a substantial amount of particles flows through the OGVs and erode the PS, while fewer particles from the lower sections of the fan blade pass via the IGVs to the engine's core. These findings highlight erosion-prone regions that require special protective coatings.

It was shown how we can describe microscopically the Andreev current in a uniform way for a contact with direct coupling between N and S leads and with intermediate chain of atoms (multilayer system) inside the contact. Considering various types of connection of the normal lead to external thermal bath we reproduce various nonequilibrium distributions at the edge of the normal lead. It was shown what type of connection to the external reservoir corresponds to the classical result of Blonder,Klapwijk and Tinkham. Also we discuss difference in equilibrium and non equilibrium proximity effect, and it is clarified that the Andreev current arises due to the nonequilibrium effects which is much larger than the equilibrium one. Contribution for the JETP special issue in honor of P. L. Kapitza’s 130th anniversary

Quasi-direct current (Q-DC) filamentary electrical discharges are used to control the shock train in a back-pressured Mach 2 duct flow. The coupled interaction between the plasma filaments and the shock train leading edge (STLE) is studied for a variety of boundary conditions. Electrical parameters associated with the discharge are recorded during actuation, demonstrating a close correlation between the STLE position and dynamics. High-speed self-aligned focusing schlieren (SAFS) and high frame-rate color camera imaging are the primary optical diagnostics used to study the flowfield and plasma morphology. Shock tracking and plasma characterization algorithms are employed to extract time-resolved quantitative data during shock–plasma interactions. Four distinct shock–plasma interaction types are identified and outlined, revealing a strong dependence on the spacing between the uncontrolled STLE and discharge electrodes and a moderate dependence on flow parameters.

Multiple engineering projects have confirmed that hydraulic machinery operating in sediment-laden rivers undergoes sediment abrasion. Guide vanes are among the most severely worn flow-passing components and have long been a key research focus in hydraulic machinery. In this research, a wear test of the NACA0012 cascade under a 10° incoming flow angle was carried out in the Venturi test system, and the evolution process of the wear was analyzed. The three-dimensional flow channel of the cascade was constructed, and the Finnie wear model was adopted for computational fluid dynamics (CFD) simulations to analyze the wear mechanism at the initial stage. The results indicate that abrasion primarily occurs at the airfoil’s leading edge and progresses through three stages: initiation, development, and stabilization. The calculated results closely matched the latest wear outcomes: In the initial stage, the wear rate density was influenced by the particle impact velocity, angle, volume fraction, and y-direction shear stress. A low-velocity zone near the impact point, combined with rebounding particles causing secondary impacts, increases the particle volume fraction and wear rate density. These secondary impacts are the primary causes of erosion on both the upstream and downstream surfaces. Furthermore, flow separation downstream from the leading edge makes this region highly susceptible to wear. This study provides valuable insights for addressing wear in hydraulic machinery for practical engineering applications.

The objective of this paper is to investigate the effect of a passive control method on the incipient cavitation mode around a hydrofoil. Two micro vortex generators (mVGs) with different positions are installed on the leading edge (LE) of the NACA (National Advisory Committee for Aeronautics) 66 hydrofoil. The mVG-1 has the same structural parameters as the mVG-2, but it is closer to the LE of hydrofoil. A high-speed camera is used to record the transient behavior of the cavitating flow. The large eddy simulation combined with a mass transport model is applied to analyze the influence mechanism of mVG on the incipient cavitation mode. The results show that the three typical incipient cavitation modes are observed on the baseline hydrofoil, i.e., spot cavity, patch cavity, and finger cavity. The mVG induces the generation of vortex shaped like thin strips of fingers at its trailing edge, called the fingerlike vortex cavitation. The neighboring fingerlike vortices constitute a pair of counter-rotating vortices with equal sizes and opposite directions. It influences the near-wall flow state upstream and downstream of mVG and, thus, the incipient cavitation structure. For the mVG-1 hydrofoil, the fingerlike vortex cavitation is a unique form of the incipient cavitation mode, making the cavitation onset position fixed at the mVG tail. For the mVG-2 hydrofoil, the mVG has a significant effect on the incipient cavitation structure at small attack angles, changing both the incipient cavitation mode and position.

The occurrence of cavitation in hydraulic machinery is a matter of significant concern, as it presents a substantial risk to the reliable functioning of pump jet propulsors. The point of this study is to find out how well bionic blades with different kinds of leading edge (LE) tubercles distribution stop cavitation in high-speed pump jet propulsors. Furthermore, it examines their performance in various cavitation scenarios. The study conducts a thorough evaluation of the function of bionic blades in mitigating cavitation and maintaining performance by analyzing head, efficiency, cavitation shape, pressure distribution, entropy production, vortex flow, and pressure pulsations. In the absence of reaching the cavitation critical point, the bionic blade 1 (BB1) model exhibited a head that was 2.65% greater than that of the original blade (OB) model. Additionally, it had the highest level of effectiveness among the three bionic blades in preventing cavitation, causing a 5%–8% delay. Furthermore, the LE tubercles not only successfully inhibited cavitation but to some degree stimulated the formation of both tip clearance cavitation and tip leakage cavitation. The BB1 model did a better job of controlling entropy production and vortex flow during the inception to collapse of cavitation. This led to lower losses, more consistent flow properties, and higher efficiency compared to the OB model. Analysis of the pressure pulsations shows that BB1 exhibits a reduction in pulsation intensity across all cavitation numbers, indicating excellent dynamic stability.

While bionic designs show significant promise in improving the hydraulic performance of fluid machinery, achieving these benefits in engineering applications requires meticulous design and optimization. Inspired by the biomimetic features of humpback whale and Atlantic bluefin tuna, we proposed a bio-inspired design approach to collaboratively optimize both the impeller and diffuser of slanted axial-flow pumps, incorporating leading-edge (LE) tubercles and trailing-edge (TE) serrations. To improve the overall hydraulic performance, several geometric design variables of LE tubercles and TE serrations were considered using a surrogate model for multi-objective optimization. In contrast with the baseline case without bionic design, LE tubercles and TE serrations significantly improved the hydraulic performance under overload conditions, increasing the head and efficiency by up to 7.59% and 3.47%, respectively. In particular, we found that the wavy shape of the LE tubercles promoted a more gradual pressure distribution around the impeller, reducing the formation of low-pressure regions near the suction side that lead to cavitation and decreasing the cavitation bubble volume by up to 19.40%. TE serrations were shown to minimize flow separations and vortex shedding, thereby stabilizing vortex patterns and reducing transverse flow between the serrations. Optimizing the TE serrations resulted in a 16.38% decrease in discharge passage loss compared to the baseline. Extending the TE serration section helped to reduce flow deviation in the outlet passage, decreasing the deviation coefficient by up to 17.46% under rated condition. An experimental comparison validated the advantage of the bio-inspired design approach.

The December issue of TLE features a special section about reservoir characterization. This file includes the entire issue in PDF format.

The Editorial Calendar details upcoming publication plans for The Leading Edge.

In modern warfare, various jamming techniques are employed to disrupt enemy radar systems using radio waves. The pull-off deceptive jamming technique misguides the enemy into incorrectly detecting the positions of allies, causing it to waste radar resources while protecting friendly information. The development and advancement of digital radio frequency memory (DRFM) have enabled the precise replication of received radar signals, making it difficult to distinguish between the deceptive range and velocity signals generated through this technique and signals reflected from actual targets. To address this, a countermeasure technique was developed that exploits the fact that a delay occurs when analyzing and replicating signals by focusing on detecting only the leading edge of the received signal to eliminate deceptive signals. This study simulates air-to-air radar operating environments and analyzes the performance of a leading-edge tracker-jamming countermeasure technique based on various indicators.