Tip Region Research Articles

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.

Finite domain solution of a hydraulic fracture in a permeable rock

In this work, we present a domain-based algorithm to simulate the propagation of a plane-strain hydraulic fracture in a zero-toughness permeable elastic medium. The algorithm utilizes a domain-based method to solve the elasticity equations and integrates a multi-scale tip asymptote, which is particular to hydraulic fractures, into this framework. This integration is key to accurately model the energy dissipation and the fluid leak-off in the fracture tip region. The algorithm combines a 2D finite volume method (FVM) for solving the elasticity equation with a 1D FVM for solving the nonlinear lubrication equation. Incorporating the far-field asymptotics and using a moving-mesh scheme reduces the computational burden while improving the accuracy of the scheme. The paper concludes with an analysis of the numerical results. This study demonstrates the potential of this domain-based approach for modeling hydraulic fractures in poroelastic media.

Evolution of large-scale flow structures in an axial-flow pump during performance breakdown

This paper presents a very large eddy simulation analysis of the unsteady flow in the pre-stall to stall transition process of an axial-flow pump, with the aim to elucidate the spatiotemporal evolution of large-scale flow structures during the performance breakdown of the pump. The transient flow is investigated utilizing a time-dependent flow rate computation scheme. The results demonstrate that, as the flow rate is dynamically reduced, the reduction in pump head is found lags behind the reduction in flow rate by approximately 15 impeller revolutions. The leading edge separation on the blade suction side (SS) evolves into a leading edge separation vortex (LSV) in conjunction with the dynamic reduction in flow rate. The attached flow on the SS in the vicinity of the hub and blade trailing edge squeezes the mainstream outwards, resulting in the formation of a cross passage vortex (CPV) on the tip side of the passage. The combined effect of the LSV, CPV, and tip-clearance flow induces a penetrating upstream flow in the tip region of the impeller, which gives rise to a swirling backflow within the inlet pipe. At stall, the CPV is stably attached to the SS and extends upstream of the leading edge of the neighboring blade. Furthermore, a trailing edge backflow is observed near the junction of the blade trailing edge and the hub, and it collides with the inflow near the hub, resulting in the formation of a hub-attached vortex.

Microstructure forming mechanism of inconel 625 alloy fabricated by laser/ultra-high (UHF) induction hybrid deposition method

To reveal the microstructure forming mechanism of laser/ultra-high frequency (UHF) induction deposition, this paper developed a microscopic phase-field (PF) model to numerically investigate dendrite growth during solidification. The macroscopic model of molten pool evolution is adopted to provide the solidification conditions for the microscopic PF model. The dendrite growth during laser deposition is simulated to evaluate the effect of UHF induction heat on the dendrite growth. Results show that because of the high temperature gradient and cooling rate, the PDAS of laser-UHF induction hybrid deposited layer is less than that of the laser deposited layer. The UHF induction heat also leads to a high flow velocity of the molten metal during laser-UHF induction hybrid deposition. The high flow velocity contributes to the decrease in PDAS by inhibiting the interdendritic enrichment of solute. During laser-UHF induction hybrid deposition, a higher solute gradient is present in the tip region of dendrite arm, leading to a faster dendrite growth rate. The UHF induction heat also increases the solute distribution coefficient during deposition, which further inhibits the element segregation. Under the action of UHF induction heat, a low interdendritic solute gradient and an evenly distributed solute can be obtained, thus helping increase interdendritic undercooling degrees and decreasing the PDAS. The simulated PDAS and solute distribution have good consistency with the experimental results. The spectral analysis of EDS line detection indicates that the laser-UHF induction hybrid deposited layer has a more refined microstructure and weaker element segregation than the laser deposited layer does.

Deformation behavior of plastic zone at crack tip of 304 stainless steel

AbstractIn this paper, the deformation behavior of plastic zone at crack tip during crack propagation of 304 stainless steel was studied. Firstly, the fatigue crack propagation tests of 304 stainless steel material were carried out. Combined with digital image correlation (DIC) technology, the strain field data of plastic zone at crack tip, the size of plastic zone, and the strain evolution law of crack tip region at different positions were obtained. Then, combined with the theoretical model and the numerical model, the theoretical, numerical, and experimental results were compared to verify the accuracy of the model. Finally, the effects of cyclic loading, specimen thickness, and weld position on plastic zone at crack tip were analyzed. The research results provide a reference for accurately predicting the fatigue crack growth of 304 stainless steel.

Numerical investigation into rotating instability and the vortex structure near the tip in a transonic compressor rotor

An unsteady simulation with a full-annular computed domain was conducted to explore the flow unsteadiness near the tip region and the mechanism of rotating instability (RI) in the transonic rotor. The numerical static pressure signals were monitored at the tip region. RI was identified by a frequency hump in the spectrum of the static pressure signal in a small mass flow coefficient with a narrow range of 0.9510–0.9174. The cross-power spectrum of two static pressure signals obtained in adjacent passages showed that the circumferential propagation speed of RI decreased with the decrease in the mass flow coefficient. The relative circumferential propagation speed of RI of the prominent mode order was −0.65 to −0.61 times the rotor speed. Details of the flow field near the tip showed that a new vortex structure was induced by the interaction of the tip leakage vortex and the shock wave, which was called as tip secondary vortex (TSV). The TSV was the key parameter to the formation of RI. The impact of the TSV on the pressure side surface generated a low-pressure area and changed the tip load of the adjacent blade. RI is result of the propagation of the interaction between the TSV and the tip load.

The loss mechanisms and vortex dynamics of rotor platform step geometries in a low-speed research compressor stage

The construction and assembly of an axial compressor blade row introduces real geometric features, which leads to the deviation of flow characteristics from the intended design. According to the realistic assembly errors observed in the four-stage low-speed research compressor developed by Shanghai Jiao Tong University, two representative step geometries at the rotor platform were abstracted. Unsteady simulations were carried out in the stage environment to study the influence of hub discontinuities on compressor performance and loss mechanisms. The comparisons of smooth hub, elevated hub (EH), and a wedged hub (WH) demonstrated that all the step geometries resulted in increased loss inside both rotor and stator rows. The loss induced by WH was more sensitive to step heights than EH. Under the influence of forward facing step, rotor incidence was reduced and horseshoe vortex (HV) was exacerbated, leading to the accumulation and separation of low momentum fluids at the pressure side corner. This led to a redistribution of losses across the span. In the lower half span, the relative total pressure loss increased almost linearly with step heights, while in the tip region, it reduced slightly. The backward facing step generated the step corner vortices (SCV) that shed and propagated downstream. The SCV interacted with the HV and cavity leakage vortex in the stator passage. Coupled with the augmented stator inflow angle, the corner separation at the suction side was dramatically intensified and led to a significant loss increase.

Twist Angle Error Statistical Analysis and Uncertain Influence on Aerodynamic Performance of Three-Dimensional Compressor Rotor

Twist angle errors along the blade radial direction are uncertain and affected by cutting force, tool wear, and other factors. In this paper, the measured twist angle errors of 13 sections of 72 rotor blades were innovatively analyzed to obtain the rational statistical distribution. It is surprisingly found that the under-deflection systematic deviation of twist angle errors shows a gradually increasing W-shaped distribution along the radial direction, while the scatter is nearly linear. Logically, the statistical model is established based on the linear correlation of the scatter by regression analysis to reduce variable dimension from 13 to 1. The influence of the radial non-uniform twist angle errors’ uncertainty on the aerodynamic performance of the three-dimensional compressor rotor is efficiently quantified combining the non-intrusive polynomial chaos method. The results show that the mean values of mass flow rate, total pressure ratio, and isentropic efficiency at the typical operating conditions are lower than the nominal values due to the systematic deviation, indicating that the under-deflection twist angle errors lead to the decrease in compressor thrust. The compressor’s stable operating range is more sensitive to the scatter of twist angle errors, which is up to an order of magnitude greater than that of the total pressure ratio and isentropic efficiency, indicating the compressor’s safe and stable operation risk increases. Additionally, the flow field at the tip region is significantly affected by twist angle errors, especially at the shock wave position of the near-stall condition.