Radial Rim Research Articles

The role of non-uniform magnetization texture for magnon–magnon coupling in an antidot lattice

We numerically study the spin-wave dynamics in an antidot lattice based on a Co/Pd multilayer structure with reduced perpendicular magnetic anisotropy at the edges of the antidots. This structure forms a magnonic crystal with a periodic antidot pattern and a periodic magnetization configuration consisting of out-of-plane magnetized bulk and in-plane magnetized rims. Our results show a different behavior of spin waves in the bulk and in the rims under varying out-of-plane external magnetic field strength, revealing complex spin-wave spectra and hybridizations between the modes of these two subsystems. A particularly strong magnon–magnon coupling, due to exchange interactions, is found between the fundamental bulk spin-wave mode and the second-order radial rim modes. However, the dynamical coupling between the spin-wave modes at low frequencies, involving the first-order radial rim modes, is masked by the changes in the static magnetization at the bulk–rim interface with magnetic field changes. The study expands the horizons of magnonic-crystal research by combining periodic structural patterning and non-collinear magnetization texture to achieve strong magnon–magnon coupling, highlighting the significant role of exchange interactions in the hybridization.

Spin-wave spectra in antidot lattice with inhomogeneous perpendicular magnetic anisotropy

Magnonic crystals are structures with periodically varied magnetic properties that are used to control collective spin-wave excitations. With micromagnetic simulations, we study spin-wave spectra in a 2D antidot lattice based on a multilayered thin film with perpendicular magnetic anisotropy (PMA). We show that the modification of the PMA near the antidot edges introduces interesting changes to the spin-wave spectra, even in a fully saturated state. In particular, the spectra split into two types of excitations: bulk modes with amplitude concentrated in a homogeneous part of the antidot lattice and edge modes with an amplitude localized in the rims of reduced PMA at the antidot edges. Their dependence on the geometrical or material parameters is distinct, but at resonance conditions fulfilled, we found strong hybridization between bulk and radial edge modes. Interestingly, the hybridization between the fundamental modes in bulk and rim is of magnetostatic origin, but the exchange interactions determine the coupling between higher-order radial rim modes and the fundamental bulk mode of the antidot lattice.

Numerical investigation of the purge flow mechanisms and heat-transfer characteristics of turbine rim seals

In gas turbine and aeroengine, the rim seal is set between the turbine stator and rotor to prevent ingestion of the high-temperature mainstream into the rotating cavity. This study examined the sealing efficiency, flow mechanisms, and heat-transfer characteristics of three types of radial rim seal structures, which seriously affect the turbine aerodynamic efficiency and thermal safety. The flows and thermal fields were simulated using steady and unsteady numerical simulations, and dynamic modal decomposition was carried out to extract the unsteady characteristics. The results show that the seal cavity shape affects the seal efficiency. It was found that dolphin-nose with a hook and large cavity results in a higher sealing efficiency. The nose configuration of the cavity upper part also affects the outflow form of the purge flow. The purge flow from a shark-nose seal will inhibit the strength of the mainstream passage vortex, while that from a dolphin-nose seal will result in Kelvin-Helmholtz instability under certain flow rates and induce unsteady vortices. The purge flow will increase the thermal load of the blade and the hub at low flow rates. In particular, the overall thermal load with a dolphin-nose seal is 50% higher than that with a shark-nose structure. It is necessary to balance the sealing efficiency, flow instability characteristics, and heat-transfer characteristics to select an appropriate rim seal configuration.

Effects of an Impeller Rim and Radial Clearance on Energy Characteristics of an Axial Pump

The results of numerical and experimental research conducted in the Laboratory for Hydraulic Machinery Construction of Peter the Great St. Petersburg Polytechnic University are presented. The research is aimed at studying the effects of an impeller radial clearance and rim on the energy characteristic of low-pressure axial pumps of the specific speed ns≈600. It is shown that these design features of a flow duct have significant effects on stage parameters, and they have to be accounted for when verifying design and experimental characteristics of axial pumps.

Effect of protrusion amount on gas ingestion of radial rim seal

In this paper, the effect of different amount of protrusion on various parameters in rotor–stator system was experimentally studied by measuring CO2 concentration and pressure, in order to obtain the optimal protrusion amount. The parameters of different dimensionless sealing flow were measured under the condition that the annulus Reynolds number was 4.39 × 105 and the rotating Reynolds number was 1.05 × 106. The results show that the change of the amount of protrusions has little effect on the static pressure in the cavity, and the static pressure change near the sealing ring is almost negligible. But the total pressure and sealing efficiency increase first and then decrease with the increase of the amount of protrusion. The variation of power consumption is the same. A complex vortex structure will appear at the high radius region when the protrusion is installed. On the other hand, the protrusion can effectively reduce the minimum sealing flow of the rotor–stator cavity. Furthermore, considering the sealing efficiency and power consumption, the best range of the protrusion amount is about 36. The ratio near this range can optimally balance the alleviation of the gas ingestion and the reduction of the power consumption.

Rotationally-induced unstable flow characteristics and structural optimization of rim seals

In view of rotationally-induced unsteady rim sealing flow issues in the absence of mainflow nonuniform pressure fields, the large eddy simulation method validated by the enclosed rotating cavity flow measurement was adopted to investigate the instability of the flow in the enclosed rim seal cavity. On this basis, the unsteady Reynolds-averaged numerical calculation was carried out for three structures: typical axial and radial rim seals as well as the chute seal that is visible in actual engines. The unsteady sealing flow characteristics for typical rim seal structures are investigated. The dynamic characteristics of the large-scale vortex structures in the rim seal region are revealed by fast Fourier transform and cross-correlation analysis methods. Finally, the rotationally-induced sealing characteristics for different rim seal structures and the enlightenment of the seal structure optimization are given. The results show that the rotationally-induced rim sealing flow has inherent instability characteristics; a series of large-scale vortex structures are generated in the rim clearance region, which propagate in the circumferential direction at a speed lower than the rotor, and the vortex frequency, number of revolutions and number of vortices depend on the rim seal type; overall, the chute rim seal has the highest rotationally-induced sealing effectiveness.

Numerical Investigations on the Sealing Effectiveness of Turbine Honeycomb Radial Rim Seal

This paper presented a numerical comparison of the sealing performance between conventional radial rim seal and new-designed honeycomb radial rim seal with three sealing flow rates. Three-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) equations, coupled with a fully developed shear stress transport (SST) turbulent model from ansys-cfx, were utilized to investigate the sealing effectiveness of rim seal and flow characteristics in the wheel-space of gas turbines. First, the numerical method for analysis the sealing performance of the rim seal was validated on the basis of published experimental data. Pressure distributions on the vane hub, sealing effectiveness distributions on the stator disk surface and swirl ratio distributions in the wheel-space of the experimental models were numerically computed and compared to the experimental data. The additional scalar variable was adopted in calculation to simulate the distribution of tracer gas concentration in experiment. The numerical results were in excellent agreement with experimental data. Then the sealing effectiveness of conventional and new-designed honeycomb radial rim seal are compared. The flow field in the wheel-space of the new-designed honeycomb and conventional turbine radial rim seal was illustrated and analyzed. Furthermore, three cases with different honeycomb cell depths were selected to investigate the influence of honeycomb cell depth on sealing performance of honeycomb radial rim seal. Compared with conventional radial rim seal, the honeycomb radial rim seal could improve the sealing effectiveness by 9–14% at the same sealing flow rate. The honeycomb cell depth has a pronounced effect on sealing performance of honeycomb radial rim seal. It shows that sealing effectiveness of the honeycomb radial rim seal increases with the increase of the honeycomb cell depth, as honeycomb cell depth increases from 1.6 mm to 4.8 mm, the sealing effectiveness is increased by about 8% at most. In addition, the flow pattern of the rim seal and wheel-space is provided to describe sealing flow characteristics.

Scaphoid fracture combined with triangular fibrocartilage injury and radial head fracture: a new type of forearm injury triad

Objective To introduce a new triad of forearm injury: scaphoid fracture, triangular fibrocartilage (TFC) injury and radial head fracture, and discuss the similarities and differences comparing to Essex-Lopresti injury. Methods Six male patients of closed forearm injuries treated from October 2011 to May 2013 were involved in this study. They all had scaphoid and radial head fractures on the same side. Wrist arthroscopic examination was carried out in 3 cases that revealed injury to the radial rim of the TFC. One case had olecranon fracture on the contralateral side, while 5 cases had no other accompanying fractures.Two cases were non-surgically treated, while 4 cases were surgically managed where the scaphoid fracture was treated with percutaneous compressive cannulated screw fixation, and the laceration or perforation at the radial rim of the TFC revealed under wrist arthroscopy in 3 cases was treated with arthroscopic debridement. The radial head fracture in 3 cases was categorized as Mason type Ⅰ and treated with splint immobilization. Open reduction and internal fixation was used in 1 case of Mason type Ⅱ radial head fracture. Results All 6 patients were follow-up for 12 to 24 months. The mean follow-up period was 17 months. Fracture union was achieved in all six patients. Clinical evaluations using modified Mayo wrist scoring system and modified Morrey elbow score revealed excellent wrist and elbow functional results in all the patients. Conclusion Comparing to the typical Essex-Lopresti injury, the reported new triad of forearm injury has subtler clinical manifestations due to the relatively low energy impact despite of the similar injury mechanisms. Consequently, misdiagnosis or missed diagnosis is more likely to happen. Successful outcomes rely on prompt diagnosis and proper treatment. Key words: Scaphoid bone; Radius; Fractures, bone; Triangular fibrocartilage

Numerical investigation of the effect of rim seal on turbine aerodynamic design parameters and end wall flows in low-aspect ratio turbine

Turbomachinery design is associated with a comprehensive understanding of the end wall loss mechanism which is more complicated when the rim seal purge flow is taken into consideration. Ensuring an adequate life of high pressure turbine requires efficient cooling method to keep the disk temperature at an acceptable level. Hence, purge flow is injected through the rim seal in axial turbine in order to prevent hot gas ingestion into the rotor disk. This paper focused on the effect of upstream rim seal purge flow on turbine aerodynamic design parameters in a low aspect ratio axial turbine. Besides, end wall secondary flows and interaction between the rim seal purge flow and mainstream were also highlighted. Two different rim seal configurations were taken into account, i.e., inclined axial rim seal configuration and radial rim seal configuration. The purge flow rate approximately equaled to 1% of main flow which is the typical value in modern aero-engine secondary air system. Results show that inclined axial rim seal configuration is obviously superior to the radial one in terms of aerodynamic and sealing performance. The turbine aerodynamic design parameters and end wall flows are significantly modified by the purge flow. The change of pressure field and vortex structure near the hub region directly leads to the variation of turbine aerodynamic design parameters. In addition, the pressure leg of horse shoe vortex nearly disappears and cavity induced vortex appear when the flow is injected from rim seal. Moreover, the two legs of cavity induced vortex have the same rotating direction which form the passage vortex and propagate downstream in the main passage. Current research demonstrates that it is important to consider the effect of rim seal purge flow in turbine aerodynamic design and end wall profile optimization.

Design of a New Kind of the Radial Annular Seal for the Aeroengine

To minimize fluid leakage loss and improve rotordynamic stability of traditional aeroengine seals, a new kind of radial annular rim seal (RARS) is presented in this paper. Comparing with the conventional labyrinth rim seal (LRS), the fluid leakage direction is modified from the axial to radial direction. The flow resistance increases, and the flow-induced force is greatly reduced. The completed three-dimensional CFD model between RARS and LRS were employed to analyze the inherent characteristics of the fluid flow in the whole passage. Calculated results show that RARS has less leakage and fluid-induced force compared to the LRS.

Radiological radio-carpal and mid-carpal motion after operative treatment of dorsal radio-carpal fracture dislocations

Radio-carpal fracture dislocations are rare severe injuries typically seen following high energy trauma. This injury is characterized by complete dislocation of the radio-carpal joint with avulsion fracture of dorsal or palmar cortical rim of the distal radius combined with disruption of the radio-carpal ligament complex. The purpose of our study is to assess the radiological motion outcome of the radio-carpal joint after Moneim type 1 radio-carpal fracture dislocations following surgical treatment. Only Moneim type 1 injuries were included in this study. Eight patients with Moneim type 1 injuries were identified by retrospective examination of our fracture registry and included in this study. All patients were initially treated with closed reduction and plaster immobilization. CT scans were performed after reduction. Operative treatment consisted of anatomic reduction of the distal radial rim fractures and fixation with a small T-plate through a dorsal approach. Cancellous bone graft was utilized if necessary to support the articular surface. Repair of the palmar radio-carpal ligament complex was performed through a palmar wrist approach. Antero-posterior, lateral, as well as lateral flexion and extension radiographs were taken at an average follow-up of 4.1 years. Follow-up radiologic evaluation of standard lateral radiograph revealed a mean scapholunate angle of 55.6°. The mean capitolunate angle was found to be −11.6° and the mean radio-capitate angle was 10.5°. The average noted angles in maximum flexion were as follows: radiolunate 15.3°, capitolunate 18° and radiocapitate 30°. The average angles in maximum extension were: radiolunate −23.9°, capitolunate −31° and radiocapitate −55°. At follow-up, arthritic changes were assessed radiographically using the classification described by Knirk and Jupiter. Fifty-six percent of the patients were found to exhibit stage 1 traumatic arthritis, 33% had stage 2 traumatic arthritis and 11% exhibited stage 3 traumatic arthritis with radio-carpal joint space obliteration. Rigid bony fixation and palmar radio-carpal ligament repair of Moneim Type 1 radio-carpal dislocations resulted in preservation of sagittal plane motion of the proximal carpal row in eight of nine cases. Our data suggest that surgical reconstruction of Moneim type 1 injuries is the preferred treatment and usually leads to satisfactory range of motion.

Flexor Tendon Injuries Following Locked Volar Plating of Distal Radius Fractures

We present 2 cases showing that flexor pollicis longus and flexor digitorum profundus index injury can occur after placement of 2 commonly used locked volar plates. In contrast with the literature, the radii healed in an anatomic position without plate lift-off. The patients presented 6 and 8 months after surgery with new onset of radial wrist pain and tenderness at the site of the plate and absence or weakness of the flexor pollicis longus. In both cases, the plate was positioned anterior to the distal radial rim on the lateral radiograph. We suggest close follow-up of all fractures in which the distal end of the plate is anterior to the radial rim and removal of hardware if symptoms suggest tendon irritation.

Triangular Fibrocartilage Complex and Lunotriquetral Ligament Injury of Distal Radius Fracture

Purpose: The purpose of this study was to assess the relationships between the pattern of fractures and associated intra-articular soft tissue injuries. Materials and Methods: We performed a study of 31 patients treated for distal radius fracture. Radiographic evaluation included ulnar styloid process fracture, dorsal anglulation and ulnar variance. We observed TFCC injuries, scapholunate and lunotriquetral ligament injuries by arthroscopy. Results: The incidence of TFCC radial rim tear and lunotriquetral ligament injuries were significantly higher in die punch fractures with lunate facet involvement than in fractures without lunate facet involvement (p0.05). Conclusion: The TFCC radial rim and the lunotriquetral ligament may be injured by axial compression loading of the ulnar head on the triquetrum. TFCC radial rim tear and lunotriquetral ligament injuries must be kept in mind in die punch fractures with lunate facet involvement.

Palmar dislocation of the radiocarpal joint

Radiocarpal dislocation, with or without damage to the radial styloid process or to the distal radial rim, is extremely rare. Review of the literature reveals much confusion on the proper classification of radiocarpal dislocations or fracture-dislocations. A case of radiocarpal dislocation is reported, the classification is discussed, and a critical review of earlier reports is presented.