Tip Region Research Articles

Exploring the conformational space of the mobile flap in Sporosarcina pasteurii urease by cryo-electron microscopy.

To fully understand enzymatic dynamics, it is essential to explore the complete conformational space of a biological catalyst. The catalytic mechanism of the nickel-dependent urease, the most efficient enzyme known, holds significant relevance for medical, pharmaceutical, and agro-environmental applications. A critical aspect of urease function is the conformational change of a helix-turn-helix motif that covers the active site cavity, known as the mobile flap. This motif has been observed in either an open or a closed conformation through X-ray crystallography studies and has been proposed to stabilize the coordination of a urea molecule to the essential dinuclear Ni(II) cluster in the active site, a requisite for subsequent substrate hydrolysis. This study employs cryo-electron microscopy (cryo-EM) to investigate the transient states within the conformational space of the mobile flap, devoid of the possible constraints of crystallization conditions and solid-state effects. By comparing two cryo-EM structures of Sporosarcina pasteurii urease, one in its native form and the other inhibited by N-(n-butyl) phosphoric triamide (NBPTO), we have unprecedently identified an intermediate state between the open and the catalytically efficient closed conformation of the helix-turn-helix motif, suggesting a role of its tip region in this transition between the two states.

On unsteady flow characteristics in a water-jet pump based on proper orthogonal decomposition method under different inflow conditions

Considering the complex flow characteristics of the water-jet pump and the anisotropy of Reynolds stresses, a hybrid Reynolds-averaged Navier–Stokes/large-eddy simulation method based on von Kármán scale and nonlinear correction has been developed, while its effectiveness has also been verified. The proper orthogonal decomposition method is employed to study the unsteady flow characteristics inside a water-jet pump due to its advantages in flow field analysis. The internal and external characteristics of the water-jet pump under two kinds of inflow conditions are comparatively analyzed, and the intrinsic influence mechanism of nonuniform inflow on the performance of the water-jet pump is investigated. The results indicate that nonuniform inflow causes the overall decrease in the pump head curve, and occurs serious reverse flow at impeller outlet near blade tip region, which in turn generates a large energy dissipation. The flow state is relatively smooth under uniform inflow condition, while the nonuniform inflow makes tip leakage flow induce many unstable flow structures, causing large turbulent kinetic energy and low pressure difference between the pressure surfaces and suction surfaces of impeller blades. There are multiscale flow structures in the water-jet pump, with large scales corresponding to low-order modes, which play a dominant role in turbulent movement and can be used as an important element for evaluating hydraulic performance. The energy content of low-modes is lower and the distribution of flow structures in each-order mode is more chaotic in the water-jet pump for nonuniform inflow compared to the ones for uniform inflow.

Study Of Tandem Rotor Dual Wake Interaction With Downstream Stator Under Unsteady Numerical Approach

Abstract This paper highlights the intricate rotor-stator interaction between a tandem bladed rotor and a single-bladed stator in the light of unsteady numerical simulations. A low speed tandem bladed compressor stage has been conceptualized and experimentally validated against targeted performance goal. With the evident pressure rise capability of the tandem bladed compressor stage, it becomes obligatory to investigate the rotorstator interaction owing to its dominant effect on overall stage performance. The multi-passage rotor-stator unsteady simulations have been performed using blade transformation methods in ANSYS CFX. Due to the presence of two highly loaded rotor blades, the tandem rotor exhibits peculiar rotorstator interaction in terms of multiple wake impingement on the stator. Incorporating tandem blading on the rotor instead of the stator (which is more common) constricts the design envelope in terms of choice of blade axial overlap and percentage pitch. The variation of aerodynamic loading from hub to tip for both the rotor blades results in spanwise varying wake strength. The initially distinct wake structures merge resulting into a thicker wake. Additionally, the rotor blades are highly loaded in the tip region which results in the complex interaction between end-wall boundary layer and tip leakage flow. Cumulatively, these conditions constitute a challenging aerodynamic field for the downstream stator. The study focuses on the qualitative interaction between the rotor wakes and blockage with the downstream stator and put forwards some aspects of the tandem rotor-single stator stage design especially for core compressors of aero engine application.

Structural changes in Nelumbo flower petals during opening and closing.

Nelumbo nucifera is one of several plant species with flowers that typically open in the early morning and close by noon. This movement normally repeats for 3 days, with all petals falling off on day 4. However, detailed observations of flower movement in Nelumbo species are limited. Movement of flowers on plants in growth chambers were observed using time-lapse photography. Petals were examined with scanning electron microscopy or fixed and sectioned for light microscopy to determine whether changes in cell size contribute to petal elongation during flowering. This study is the first to microscopically observe petal cells of a Nelumbo species during flowering in controlled conditions. Petals elongated during the 4-day flowering period. Inner petals were more elongated than the outer petals. Among the basal, central, and tip regions of a single petal, the cells in the basal region enlarged the most. Outer and inner epidermal cells in the basal region of the inner petals, on both adaxial and abaxial sides, gradually enlarged during the flowering period through cycles of repeated increases as the petals opened and decreases as they closed. Petals opened and closed repeatedly as they elongated, primarily in their basal region. Cells in the basal region of the petal on the adaxial and abaxial sides periodically fluctuated in size, increased during flower opening and decreased during closing, but differences in these patterns were observed between the two sides, suggesting that one of the driving forces behind the opening and closing of flowers of Nelumbo species is the increase and decrease in the size of the petal cells.

Concave-shaped acoustic black holes with asymmetric arrangement for suppression and amplification of structural vibration

An acoustic black hole (ABH) is a wedge-shaped structure characterized by a power-law thickness profile with an exponent greater than or equal to two. In this study, we engineer an ABH with a concave shape, where both the width and thickness decrease according to power-law profiles. This configuration facilitates the focusing of elastic waves at the tip region with higher energy density than conventional constant-width ABHs. The highly focused waves are attenuated using a small amount of viscoelastic material attached near the tip of the ABH, resulting in dampened vibrations in the original structure such as a thin beam. Despite being about half the weight of the conventional ABH of equivalent length, the concave ABH achieves similar damping performance to the conventional one. When the conventional ABH is adjusted to match the weight of our concave design, the latter exhibits enhanced damping performance along with a lower cut-on frequency. Near-perfect reduction of structural vibration is attained by affixing a concave ABH to each end of the beam. By delicately adjusting their lengths and employing them asymmetrically, we manipulate the vibration mode shapes to minimize the structural vibrations. As a result, vibrations in the beam are barely perceptible under high-frequency harmonic excitation. The concave ABH, characterized by its ability to intensively focus elastic waves at its narrow and thin tip, is also suitable for vibration amplification, facilitating the detection of minute vibrations distributed in the original structure. The concave ABH offers improved performance in both wave absorption and amplification compared with conventional ABHs of the same length or weight, highlighting its potential as an alternative solution in vibration damping or sensing applications.

Study of unsteady shear flow near stall in a shrouded supercritical carbon dioxide centrifugal compressor

This study investigates the unsteady shear flow patterns and their relation with the aerodynamic instability of a shrouded supercritical carbon dioxide (SCO2) centrifugal compressor impeller using the dynamic mode decomposition method combined with detached eddy simulation. The results demonstrate that discrete shedding vortex array in the blade tip region is the dominant mode of the SCO2 shrouded centrifugal compressor impeller, with a frequency of 0.5 times the blade passing frequency. In contrast, the main flow structures in the identical impeller using ideal air consist of small-scale shedding vortices near the suction surface and the separated secondary flow. Further analysis of flow field details indicates that the shedding vortex structure inside the shrouded centrifugal impeller originates from the Kelvin–Helmholtz instability generated on the shear interface between the mainstream and the recirculation flow. The greater shear intensity within the SCO2 centrifugal impeller is the reason for the evident occurrence of vortex shedding phenomena in its flow field. Additionally, during the transition from near-stall to stall, vortex pairing phenomena happens at the throat of the centrifugal impeller due to evolutional behaviors of the vortexes. The occurrence of vortex pairing leads to faster blockage of the blade tip region and then the secondary flow spillage over to adjacent passage, ultimately resulting in reverse flow in the blade tip region and extensive blockage at the impeller inlet. The unsteady shear flow evolution clearly demonstrates the processes of stall in SCO2 shrouded impellers.

Mechanism investigation of stability enhancement by slot on a transonic compressor

Abstract As aircraft engine blades develop towards high loads and low aspect ratios, the flow conditions in the tip region of transonic compressor rotors become more complex. The interaction between shock waves and boundary layers tends to induce fluid separation, thereby reducing the stable operating range of the rotor. To enhance the stability margin of the rotor, this study employs numerical simulation techniques to design jet slots on the rotor 37. Research results show that, without compromising the performance of the rotor, the slotted rotor can effectively enhance the stability margin of the rotor at both design and off-design speeds, with increases of 60.9% and 47.9% in surge margins compared to the prototype.

Experimental Study on the Classification and Evolution of the Tip Cavitation Morphology in Axial Waterjet Pumps with Two Different Blade Numbers

Tip leakage flow and induced unstable cavitation can significantly damage the performance of axial waterjet pumps. This study investigated the impact of blade numbers on cavitating conditions in an axial waterjet pump by conducting tests of performance characteristics and high-speed photography experiments on three-blade and four-blade impellers. The results showed that the critical cavitation number σc of the three-blade impeller was larger, while the four-blade impeller flow pattern deteriorated more rapidly after σc. Various cavitation structures in the tip region were observed under different conditions, including clearance cavitation, shear layer cavitation, tip leakage vortex cavitation, and suction-side-perpendicular cavitating vortices (SSPCVs). Tip cavitation maps of the test impellers were drawn based on the flow rate coefficient and cavitation number variation. The three-blade impeller exhibited a wider range of severe cavitation, particularly with an increased occurrence of SSPCVs. With the cavitation number and flow rate coefficient decreased, the SSPCV generated from triangular cavitation cloud shedding presented an increased trend in scale and quantity. Conversely, in the case of the four-blade impeller, SSPCVs were often disrupted by the adjacent blade during migration and interfered with the tip cavitation in the neighboring flow passage.

A New Approach to Suppress Tip Leakage Flow Utilizing Induced Shock Wave in Tip Region of a Transonic Compressor Rotor

A New Approach to Suppress Tip Leakage Flow Utilizing Induced Shock Wave in Tip Region of a Transonic Compressor Rotor

Aging by autodigestion.

The mechanism that triggers the progressive dysregulation of cell functions, inflammation, and breakdown of tissues during aging is currently unknown. We propose here a previously unknown mechanism due to tissue autodigestion by the digestive enzymes. After synthesis in the pancreas, these powerful enzymes are activated and transported inside the lumen of the small intestine to which they are compartmentalized by the mucin/epithelial barrier. We hypothesize that this barrier leaks active digestive enzymes (e.g. during meals) and leads to their accumulation in tissues outside the gastrointestinal tract. Using immune-histochemistry we provide evidence in young (4 months) and old (24 months) rats for significant accumulation of pancreatic trypsin, elastase, lipase, and amylase in peripheral organs, including liver, lung, heart, kidney, brain, and skin. The mucin layer density on the small intestine barrier is attenuated in the old and trypsin leaks across the tip region of intestinal villi with depleted mucin. The accumulation of digestive enzymes is accompanied in the same tissues of the old by damage to collagen, as detected with collagen fragment hybridizing peptides. We provide evidence that the hyperglycemia in the old is accompanied by proteolytic cleavage of the extracellular domain of the insulin receptor. Blockade of pancreatic trypsin in the old by a two-week oral treatment with a serine protease inhibitor (tranexamic acid) serves to significantly reduce trypsin accumulation in organs outside the intestine, collagen damage, as well as hyperglycemia and insulin receptor cleavage. These results support the hypothesis that the breakdown of tissues in aging is due to autodigestion and a side-effect of the fundamental requirement for digestion.

Accelerated Takedown of Melolabial Interpolation Flaps at 1 to 2 weeks, Indications and Safety for Improved Patient Experience

BACKGROUND The melolabial interpolation flap is an effective surgical technique for reconstructing defects in the nasal ala and tip regions. Traditionally, this technique involves waiting for the standard 3-week period before pedicle division. OBJECTIVE To evaluate whether accelerated takedown at 1- or 2-week postflap creation is possible while maintaining the flap's viability and functionality. METHODS Retrospective cohort study at Oregon Health and Science University from 2018 to 2023. RESULTS The authors examined 67 patients who underwent reconstruction with a melolabial interpolation flap surgery, of which 50 had their flap takedown at <21 days and 17 had their takedown at 21 or more days. This analysis revealed similar complication rates for both groups. There were no increased rates of infection, necrosis, or hematoma formation in the earlier takedown group. Those undergoing earlier takedown were more likely to have a history of hypertension but less likely to have a history of diabetes, immunosuppression, and smoking, though the differences were not statistically significant. CONCLUSION This study provides valuable insights into the safety and feasibility of early melolabial interpolation flap takedown. This approach has the potential to enhance the quality of life for patients undergoing this flap by decreasing the amount of time with a pedicle.

Formation of Gold Bone Nanorods shape using copper as foreign metal ion

In this study, copper (Cu) is introduced as a foreign metal ion replacing platinum by modifying the recipe of GNBPs and the final structure obtained is gold bone nanorods (GBNRs). The aspect ratio and surface density of GBNRs were investigated by varying the growth time during the growth process from 30 minutes to 5 hours. It was found that the growth solution has been changed from colourless to light blue and violet colour with increasing growth time, indicating the formation of GBNRs. The UV-Vis analysis shows two resonance plasmon peaks for t-SPR and l-SPR at 583 nm and 766 nm with the intensity of 1.433 a.u and 2.236 a.u at the optimum 5 hours growth time. For morphological analysis, it was found that the sample with lower growth time produced gold nanosphere shapes and with increasing time, more GBNRs with large aspect ratios were produced. HR-TEM characterization reveals that bone nanorods are formed due to the influence of Cu foreign metal ions, which cause selective deposition of Au atoms onto {111} facet of gold nanorods, while simultaneously reducing the overgrowth rate of the {110} facet for the edge regions and the {100} facet for the tip regions of the nanorods. In addition, the influence of Cu foreign metal ions on the growth mechanism of Au nanoseeds into nanorods and the shape transformation of nanorods into bone nanorods are also discussed in this work. In conclusion, the GBNRs have been successfully synthesized using SMGM by induced Cu as foreign metal ions.

Application of a novel stall margin improvement indicator in optimizing casing treatment for a transonic compressor

This paper presents a multi-objective design optimization of axial slot casing treatments in a 1.5 stage transonic compressor. To perform the optimization, an in-house optimization design platform is constructed using genetic algorithm and Kriging surrogate model. The optimization objectives are the peak efficiency at the design rotating speed and the stall margin improvements at both design and off-design rotating speeds. Instead of massive unsteady simulations that are required to accurately predict the stall margin, a stall margin improvement indicator is introduced based on the time-averaged axial momentum budget analysis at the rotor tip region. With this indicator, only one steady simulation is needed to evaluate the stall margin enhancement ability of a new casing treatment design at a given rotating speed. The axial slots are parameterized with a total of eight design parameters. The meridional profiles are described with two B-spline curves to define parameters such as the size, axial position, and shape of the slots. Circumferential parameters include the open area ratio and inclination angle. When the optimization finally converges, different optimal variants are selected from the database and their effects are investigated with both experiments and numerical simulations. The detailed flow fields are analyzed in depth with results from unsteady simulations. The application of the optimal casing treatments exerts a suction and re-injection effect, pushes the interface between tip leakage flow and incoming main flow downstream and reduced flow blockage in the blade tip region. Consequently, the stability of the compressor is significantly improved.

Effect of radial inlet distortion on aerodynamic stability in a high load axial flow compressor

Radial inlet distortion induced by boundary layer separation can significantly affect the aerodynamic performance of the compressor. The effect of radial inlet distortion on the flow structure is numerically investigated in a high load axial flow compressor. The inlet boundary is determined by the experimental results at the downstream of the distortion generator. The results reveal that tip distortion leads to a reduction in the stall margin, whereas hub distortion extends it. Radial distortion redistributes the main flow toward undistorted region due to the obstructive effect of lattice ring. The deficit in axial velocity with tip radial distortion causes the rotor to operate at a higher incidence angle near the casing, while hub radial distortion alleviates the tip blade loading. The detailed three-dimensional flow field analysis indicates that increased blade loading with tip distortion shifts the trajectories of both primary and secondary tip leakage flow toward the leading edge, thereby expanding the blockage region. Conversely, hub radial distortion unloads the rotor tip region, thereby reducing the blockage region induced by tip leakage flow. Additionally, with hub distortion, the location of separation line on the blade suction surface moves closer to the leading edge, and the flow separation around the trailing edge is intensified.

Tip region vortices control based on cutback squealers in a high-loading axial turbine

Tip region vortices control based on cutback squealers in a high-loading axial turbine

Shock wave structures and vortex unsteadiness in the tip region of a transonic turbine cascade under different conditions

The tip region of transonic turbine blades (exit Mach number of 0.95) exhibits complex flow characteristics with the coexistence of multiple shock wave systems and multiscale vortices. Based on a validated detached Eddy simulation method, unsteady flow features such as the spatial-temporal dynamic evolution of tip leakage vortices (TLV) and the periodic buffet/oscillation of shock trains inside the tip gap are revealed and discussed systematically under different incidence angles (i) and heights of tip clearance. Moreover, the distinction of tip flow structures between the subsonic and transonic conditions is also manifested. Results indicate that the wandering behavior of the TLV is influenced by both the swirling strength of the vortex itself and the interaction of adjacent secondary vortices. The TLV under a tip gap of 5% blade height (h) exhibits “binary and bimodal” wandering characteristics both along the pitchwise and spanwise direction, whereas under the 1%h case, only the pitchwise wandering is prominent. The dominant characteristic frequency of the TLV wandering under different conditions falls within the spectrum range of 2.2–2.4 kHz. As for the shock trains inside the tip clearance (τ), coherently movement back and forth along the pitchwise direction with varying amplitudes can be observed, where the magnitude within the τ=1%h exceeds that observed in the τ=5%h, depending on the intensity of the shock waves. Notably, significant shock wave oscillations are present throughout the range of the chord length (c) within the τ=1%h, whereas within the tip gap of 5%h, shock wave systems exhibit more pronounced oscillations predominantly near the trailing edge.

Insights Into Turbocharger Centrifugal Compressor Stability Using High-Fidelity CFD and a Novel Impeller Diffusion Factor

Abstract Turbocharger technologies are widely applied in the modern automotive industry to meet increasingly stringent carbon emission standards. To support the continuous enhancement of these tactics, delivering improvement to the performance and stability of turbocharger compressors at low mass flow rate regimes is of paramount importance. The present paper investigated the stability of a turbocharger compressor stage equipped with a ported shroud, using high-fidelity CFD simulations. It was found that the recirculated flow passing through the ported shroud device had primary influence on the flow condition in the vicinity of the impeller tip region (80% to 100% span). This discovery facilitated the definition of a modified impeller diffusion factor (DF), which was applied to the CFD results for three different compressor geometry configurations to lead to the provision of quantitative metrics for impeller stability. Furthermore, the observed change in the limiting impeller DF along the compressor surge line indicated that the dominant components governing the instability of the entire stage had switched, i.e., the stalling behavior of the compressor stage had transitioned from impeller dominated stall to vaneless diffuser dominated stall. Additionally, the limiting impeller DF clearly showed that one of the compressor configurations with a change in the hub endwall recess around the rear of the impeller improved the impeller stability by 3%. By comparison, another configuration with a change to strut geometry in the ported shroud recirculation channel reduced the impeller stability by 10%.

Gross and scanning electron microscopic features of the oral cavity (palate, tongue, and sublingual floor) of the Egyptian long-eared hedgehog (Hemiechinus auratus aegyptius)

The study was focused on the anatomical characteristics of the Egyptian long-eared hedgehog's oral cavity by using gross and scanning electron microscopic examinations. The upper lip had an elongated T-shaped snout-like structure. The hard palate had a triangular rostral part (which had a semicircular area and a caudal ridged area with the first 3 or 4 ridges) and a caudal part (which contained seven or eight slightly oblique ridges with raphae). The diamond-incisive papilla is flanked on both sides by a groove and a fissure. The hard palate surface had glandular openings and a microplicae system. The uneven, soft palate's surface had multiple grooves and folds with 12–16 Gemmal papillae. The Gemmal papillary surface had three to four taste pores with microplicae and glandular openings. The dorsal lingual surface had six filiform subtypes: pointed (on the tip, rostral border, and median apical region), triangular (on the lateral apical and circumvallate regions), bifurcated (on the median tip only), leaf-like (on the median body region), branched (on the lateral root region), and small pointed papillae (on the median root). There were two fungiform subtypes: ovals (on the rostral border and lateral region) and rounds (on the median apical region and body). The caudal root part had a triangular arrangement of three circumvallate papillae. In conclusion, the finding confirmed its oral cavity adaptation with its insectivorous feeding habits and Egyptian environment.Graphical

Investigation of temperature assisted corrosion failure of an aircraft turbine blade

In this study, the root cause of a recurring corrosion problem at the tip of an internally cooled high-pressure turbine blade (HPT) of a turbofan engine was investigated. A two-pronged strategy was utilized involving (i) experimental techniques to identify the blade material and corrosion products, and (ii) computational methods to analyze the fluid flow over the blade. In the experimental thrust, an array of techniques was employed to determine the chemical composition, microstructure, corrosion products and microhardness values while the airflow, pressure distribution and thermal profile over the blade were found through computational paradigms. The blade was a Ni-based superalloy containing typical gamma (γ) and gamma prime (γ′) phases, with an average microhardness value of 389 HV at room temperature. SEM analysis of the corroded area revealed oxides of iron, calcium, magnesium, aluminium, and silicon (FCMAS) most of which were not part of the base alloy. To determine the temperature profile and pressure distribution on the blade, a conjugate heat transfer analysis using Ansys CFX was conducted. A combination of experimental data from the engine ground running test station and analytical equations was used to find the required boundary conditions for the computational analysis. Pressure distribution over the entire blade was found which showed higher flow velocities and cross flows at the blade tip which potentially cause erosion at that region in the presence of impurities in the incoming air. Temperature distribution over the entire blade was also obtained, and it was found that the highest temperatures for the internally cooled blade occurred at the tip region which were in the range of ∼1060 °C–1250 °C (average ∼1114 °C). The temperature on the tip was high enough to cause the melting of the impurities that ingress the coating and cause its degradation during thermal cycling. This exposes the base alloy to FCMAS and causes corrosion. These high temperatures (1060–1250 °C) also induced phase transformation and increased the brittleness (∼22 % increase in hardness) which aggravated the presence of corrosion and resulted in crack formation and blade rejection.

Inductive plasma excitation forcing configuration on reduction of tip distorted inflow effect on the aerodynamic stability of axial compressor rotor

This research delves into the mitigating impacts of dielectric barrier discharge (DBD) plasma excitation induced forcing orientation against the detrimental consequences of distinct radial tip distortions which in turn affect the axial compressor rotor performance and alters the flow structure at the tip region. Full annulus transient CFD simulation was utilized to evaluate the consequences of plasma actuation at distorted conditions with different blockage percentages. Beyond flow field and frequency analysis, the study further characterized rotor performance under different conditions by evaluating key performance metrics, including total pressure rise coefficient, stall margin variation, and span-wise rotor inlet velocity distribution. The injection of momentum caused by plasma actuators to the low-energy region behind the distortion screens proved to be effective on rotor aerodynamic stability facing radial tip distortion. In the case where 15 % of the inlet area was blocked, the stall margin varied from -8 % to -3.5 % with axial plasma actuators in action. However, the best configuration of plasma actuators for the enhancement of the stall margin and flow characteristics was identified to have opposite forcing direction with respect to the rotor rotational velocity. Additionally, these actuators suppressed frequencies caused by fluctuations in the rotor blade row tip leakage vortex, suggesting an improvement in the flow pattern within the rotor tip area.