Leakage Flow Rate Research Articles

Flow mechanism and back gap windage loss of a sCO2 radial inflow turbine with impeller scallops

The Internal flow mechanisms and windage loss in impeller back gap of a supercritical carbon dioxide (sCO2) radial inflow turbine with scallops are comprehensively investigated in this paper. The study emphasizes the effects of scallop depth and leakage outlet pressure. The results indicate that scallop structures lead to a degradation in overall turbine performance. Under design conditions, a turbine with a scallop depth ratio of 0.5 exhibits a 3.7% reduction in efficiency and a 3.4% decrease in total power compared to no scallop configuration. Furthermore, as scallop depth increases, the skin friction coefficient decreases in the disk gap while it increases for the seal in the impeller back gap. Increasing leakage outlet pressure reduces the leakage flow rate and skin friction coefficient. Fitted models for skin friction coefficient are proposed respectively. The conclusions providing valuable insights for designing and optimizing sCO2 radial inflow turbines with scallops.

Leak-Rate Through Carbon Brush Seals: Experimental Tests Versus Predictions From a Porous Medium Approach

Abstract This study presents a detailed comparative analysis between experimental leakage flow rates and numerical predictions for carbon brush seals with long bristles, utilizing a porous medium model approach. A series of tests were carried out on a static rig (without rotor rotation). The experimental setup allows tests under various interference conditions, revealing significant insights into the flow behavior through the brush seal. A numerical model based on the Darcy-Forchheimer equation is developed to interpret the complex flow dynamics within the brush seal, accounting for viscous, compressible and inertial effects. The study evaluates the impact of brush deformation and porosity on flow resistance, leveraging experimental data to refine the numerical model parameters. This investigation not only deepens the understanding of brush seal flow physics but also improves the predictive accuracy of the numerical model in simulating operational conditions.

Risk assessment of hydrogen leakage and explosion in a liquid hydrogen facility using computational analysis

In this study, the dispersion and explosion of liquid hydrogen (LH2) in leakage accidents are investigated using the Flame Accelerator Simulator (FLACS) code. The study focus was a liquid hydrogen research facility in Gimhae, South Korea. Simulations were conducted under various conditions by varying the mass flow rates (0.61 and 0.3 kg/s), directions (lateral in areas with minimal structures, lateral towards a tube trailer truck, and downward), and durations (90 and 180 s) of leakage. The results indicated that higher leakage mass flow rates produce a larger flammable cloud volume (FCV), resulting in higher maximum overpressures than that caused by lower flow rates. Downward leakage generally resulted in a larger FCV and higher overpressure than lateral leakage. The explosion characteristics were also influenced by geometry of LH2 facility, including the presence of structures in the leakage path. Contrastingly, leakage duration had a minimal effect on the maximum overpressure because an increased duration causes a greater dilution of hydrogen, only slightly expanding the FCV. According to the overpressure–impulse diagram, higher leakage flow rates cause severe health risks, approaching thresholds for lung rupture and 100% fatality. Contrary to the minor damages caused by lower leakage flow rates. High flow rates, particularly with downward leaks, can cause significant structural damage in brick buildings, potentially leading to partial demolition.

On Leakage Flows In A Liquid Hydrogen Multi-Stage Pump for Aircraft Engine Applications

Abstract A comprehensive operational characterisation of a representative, Liquid Hydrogen (LH2) aircraft engine pump is presented in this work. The implications of leakage flows are investigated in a 2-stage, high-pressure pump for a wide range of flow rates and rotational speeds, through 3D (U)RANS simulations. Two configurations are compared: a baseline model comprising the primary flow path components - inducers, impellers and volutes and a realisable pump hardware that includes hub, shroud and power unit cavities. Performance metrics, including head changes and efficiencies, are extracted both at a component and system level. Leakage flow rates of 27.6% and up to 92.9% of the overall pump flow rate are recorded at design and lowest flow points respectively. The head loss in the mid to low flow rates does not exceed 4.5%, but the efficiency diminishes by up to 13.5% at off-design operation. The component analysis indicates significant penalties in impeller efficiency. At high flow rates, the presence of leakage flows improves the overall pump performance by 43% and 27% in head rise and efficiency, due to reduced losses in volutes and connecting ducts. The characterisation of pump behaviour described in this work is crucial for developing and designing safe and predictable LH2 aircraft pumps. Contrary to LH2 pumps utilized in rocketry and for cooling in nuclear industry, aircraft pumps are required to operate with wider turn-down ratios and often at low specific speeds. Therefore, this study addresses design considerations for this enabling technology.

Quantitative analysis of hydrogen leakage flow measurement and calculation in the on-board hydrogen system pipelines

The mass flow rate of hydrogen leakage directly affects hydrogen diffusion and concentration distribution. In this paper, a test platform was constructed to measure mass flow rates during hydrogen leakage in the supply pipelines of the on-board hydrogen system. Hydrogen leakage tests were conducted under two different conditions. Mass flow rates were measured for tube fittings with various loosening angles and hydrogen supply pressures. The data were then fitted to extrapolate mass flow rates of hydrogen leakage beyond the tested conditions. Additionally, mass flow rates were measured for hydrogen supply pipelines with small holes of different shapes and sizes. The effects of pipeline size, hydrogen supply pressure, hole shape, and size on the hydrogen leakage mass flow rate were analyzed. Hydrogen leakage flow coefficients were corrected, and the accuracy of three calculation methods for hydrogen leakage flow was compared and analyzed based on the test results. The results provide a foundation for future numerical simulation models of hydrogen leakage diffusion.

Short-Term Bed Rest is not a Risk Factor for Venous Thromboembolism After Endoscopic Skull Base Surgery

IntroductionDeep venous thromboembolisms (DVT) increase morbidity in postoperative patients, and no current guidelines identify which patients undergoing endoscopic endonasal approach (EEA) to the skull base may be at increased risk. Postoperative care for these patients often includes a period of inactivity to prevent transient ICP shifts which may impact skull base reconstruction. We seek to characterize if postoperative bedrest puts EEA patients at increased risk of developing thromboembolic complications. MethodsRetrospective chart review of patients undergoing intradural surgery with primary skull base reconstruction for intraoperative CSF leak via EEA for any skull base pathology between July 2018 and May 2024 was performed yielding 221 patients who met inclusion criteria. Univariate and multivariable regression were performed with patient demographics, extent of approach, intraoperative leak flow rate, bedrest duration, presence and length of postoperative lumbar drainage (LD), and use of postoperative mechanical VT prophylaxis. ResultsThe mean age of included patients was 52.6 ± 16.8 years, 48% were male, and 3.6% of patients had DVTs. Age (OR 1.01, 95% CI 0.96-1.06, p=0.83), sex (OR 0.40, 95% CI 0.05-2.19, p=0.31), BMI (OR 0.98, 95% CI 0.87-1.07, p=0.74), extended approach (OR 0.80, 95% CI 0.13-4.36, p=0.80), CSF leak flow rate (OR 5.71, 95% CI 0.77-118.90, p=0.14), bedrest duration (OR 1.06, 95% CI 0.77-1.27, p=0.60), and presence of LD (OR 1.10, 95% CI 0.55-2.02, p=0.76) were not significant predictors of postoperative VTE incidence on multivariable analysis. ConclusionShort-term bedrest after EEA is not a risk factor for development of VTE in the immediate postoperative period.

Prediction of Leakage Flow Rate and Blow-Down in Brush Seals via 2D CFD Simulation with Porosity Correction

Brush seals are extensively used in rotating equipment, such as gas turbines and compressors, providing effective sealing while accommodating radial, axial, and angular movements between components. In this study, the performance of brush seals with and without clearances was predicted through axisymmetric 2D computational fluid dynamic (CFD) simulations using a porous media model. Because the accurate modeling of a brush seal requires the appropriate porosity to be determined and the flow resistance to be calculated, a porosity correction was performed based on the brush seal’s geometry and pressure ratio. The corrected porosity was then used to calculate the flow resistance and the leakage flow rate was predicted. Based on the results, the corrected porosity significantly improved the accuracy of the previously unreliable leakage flow rate predictions, regardless of the presence of clearances. For cases with a clearance, the blow-down effect was determined through CFD simulations for the given geometry and was compared with experimental data. The leakage flow rate predictions were highly accurate, with a relative error of less than 5% across a pressure ratio range of 1.5–4.

Experimental and numerical investigation on middle passage gap leakage with different mass flow rate and injection angle on turbine endwall

Regarding the actual installation feature of the blades and disk using tenon and mortise, the middle passage gap exists between the adjacent blades and the leakage flows out of the gap, cooling the endwall. To explore the balance between the aerodynamic and cooling performance on blade endwall in turbine cascade, this paper investigated the effect of middle passage gap leakage under various mass flow rate and injection angle configurations. Film cooling effectiveness measurement was performed with pressure-sensitive paint technique in a five-passages linear cascade. The mass flow ratio of middle passage gap leakage ranged from 0.5 % to 1.5 % with the injection angle (αm) ranging from −20° to 20°. A combined approach utilizing numerical simulations to elucidate detailed aerodynamic loss mechanisms and experimental results of middle passage gap leakage was employed. The results show that increasing the mass flow rate of middle passage gap leakage does not suppress mainstream intrusion phenomenon. Cases with injection angle generally show improved cooling performance compared to the non-injection case (αm = 0°). The least improvements are 19 % and 27.9 % for mass flow rates of 0.5 % and 1.0 %, respectively. The case with an injection angle of 20° demonstrates the best comprehensive performance, achieving higher area-averaged cooling effectiveness and lower aerodynamic loss (1.2 % and 18.9 % decrease for mass flow rates of 0.5 % and 1.0 %).

Innovative foresight for water utilities asset management using PRISM software

Our analysis aims to better understand water losses by developing a specific methodology for estimating water leak flow rates and durations. Additionally, it aims to improve asset management practices for drinking water utilities by forecasting the costs and benefits of investment and operational decisions on the network. Current utility practices are compared to a "do nothing" policy and to the potential effective asset management policies proposed by an artificial neural network (ANN) based software, PRISM. Applied to four utilities in France, our methodology provides valuable insights for enhancing water loss estimates and finding trade-off asset management policies.

Estimating and Reducing Leakages in the Water Distribution Networks of Small Settlements: The Case of Agios Germanos in the Prespes Municipality

Pressure management is a fundamental and highly effective method for the management of real losses in water distribution networks and therefore reducing non-revenue water. In this work, a methodology is developed to assess leakages in the water distribution networks of small settlements. The settlement of Agios Germanos in the Municipality of Prespes is selected as a representative case study. The hydraulic modeling of the water distribution network in the study area is used to assess the hydraulic behavior of the existing infrastructure in its current state of operation and to find critical locations to install the necessary measuring equipment (pressure sensors, flow meters, water level sensors, and pressure reducing valves). This equipment is used to calibrate the hydraulic model, estimate leakages, and manage them effectively. Minimum night flow analysis is utilized to assess leakages in the studied network based on measurements of the hydraulic parameters from the equipment installed. The effects of pressure management on leakages are then examined by assessing the relationship between the pressure and leak flow rate in the selected settlement.

UPDATED MATHEMATICAL MODEL OF THE TRUNK PIPELINE SECTION WITH LOOPING IN CASE OF LEAKAGE

Pipeline transport is the main method of moving volumes of oil and oil products, as it has several advantages, for example, quality safety and high throughput. At the same time, it also has some disadvantages, which can include the difficulty of increasing throughput without high capital investments and possible leaks and unauthorized tie-ins into pipelines, which are sometimes difficult to identify. Looping is one of the main ways to increase the throughput of the existing pipeline system, when the need to increase the volume of oil and oil products supplies requires the construction of several parallel pipelines — looping. At the same time, the basic mathematical model for calculating the section of the trunk oil pipeline with looping does not fully cover all the physical processes associated with the distribution of flows in the parallel section, which arise due to turbulences in the connection nodes, as well as head loss along the length of the jumpers. Taking into account the resulting flow redistributions, it becomes difficult to detect a potential leak, since any of the detection methods can not solve the problem with high accuracy with determining the leak coordinate with an unknown distribution of fluid flow rates in a parallel section. As part of the study, an updated mathematical model of the oil export pipeline section with looping was developed, which took into account the presence of a potential leak in the parallel section. Mathematical modeling was carried out on the basis of the assumption of a known coordinate, the effect of leakage on the redistribution of flows in a parallel section was estimated. To assess the impact of the leak, various coordinates and volumetric flow rates were set, based on the calculation results, graphs of the flow rate in looping versus its length and internal diameter were plotted. The study is the initial phase of developing a hydraulic location leak detection system for the oil export pipeline section with looping. The need to refine the mathematical model for determining the flow rate in the parallel section is an urgent and necessary task, the solution of which will allow identifying potential leaks with reliable accuracy.

Experimental study of flow control on tip leakage flow in variable geometry linear turbine cascades with different pivot layouts

Variable geometry turbines are essential for adjusting operational conditions in industrial gas turbines and variable cycle engines. These adjustments necessitate partial gaps at both ends of the variable guide vanes to alter the turning angle, consequently introducing an aerodynamic performance penalty. Moreover, the pivot layout profoundly influences aerodynamic losses. Research on turbine cascades that considers various partial gap layouts is limited, particularly in terms of experimental studies, which are rarely conducted. This study aims to diminish aerodynamic losses and augment the efficiency of gas turbines by examining the impact of pivot layouts on partial gap clearance and secondary flow. It further investigates the effectiveness of flow control strategies at the blade tip across different pivot configurations within a variable geometry turbine cascade, utilizing pneumatic probe scanning and surface oil flow visualization techniques. The results reveal that employing a cavity at the tip can significantly reduce aerodynamic losses in schemes both with and without a pivot, achieving maximum loss reductions of 15.8% and 3.7%, respectively. Additionally, a narrower squealer width can further decrease these losses. However, with a pivot located at the tip, the resulting separation flow and wake vortex become predominant sources of losses. The presence of the pivot weakens the tip leakage flow rate and the intensity of the tip leakage vortex (TLV), thus diminishing the effectiveness of cavity tip flow control. The cavity moderates TLV and enhances the interaction between TLV and the wake vortex, leading to increased aerodynamic losses.

A comparison of static and rotordynamic characteristics for two types of liquid annular seals with and without helical grooved stator

Less leakage is a benefit of parallel grooved liquid seals (labyrinth seals). But researches show that the liquid seal with parallel grooves on the rotor harms the rotor stability. The seal with helical grooves on stator performs well in terms of rotordynamics, and its leakage is sensitive to the rotating speed. To make use of the advantages of both seals and improve seal stability, based on the Smooth-stator/Parallel Grooved-rotor (SPG) liquid seal, a Helical Grooved-stator/Parallel Grooved-rotor (HGPG) liquid seal is designed. To evaluate two liquid seals’ leakage, rotordynamic characteristics and drag power loss, a transient computational fluid dynamics-based method is employed. This method is based on the multi-frequency elliptical-orbit rotor whirling model and the mesh deformation technique. The published experimental data of the leakage and rotordynamic force coefficients for an SPG liquid seal are used to validate the accuracy and dependability of the current method. Seal leakage and force coefficients are presented and compared for the SPG liquid seal and the HGPG liquid seal at various pressure drops. The influences of parallel groove depth on the leakage and rotordynamic properties for the HGPG liquid seals at two rotational speeds (2000, 6000 r/min) are analyzed. The numerical findings demonstrate that the novel HGPG liquid seal has a lower leakage flow rate (by ∼22.3%) than the traditional SPG liquid seal. There is an optimal parallel groove depth that minimizes leakage. The presented novel HGPG liquid seal significantly improves rotordynamic stability, due to the similar effective stiffness and the obviously larger positive effective damping. Reducing parallel groove depth can increase the positive effective damping. In terms of leakage and rotordynamic characteristics, the novel HGPG liquid seal is a better seal design for liquid turbomachinery.

Measurement of CO2 leakage from pipelines under CCS conditions through acoustic emission detection and data driven modeling

CO2 leakage from carbon capture and storage (CCS) networks may lead to ecological hazards, bodily injury and economic losses. In addition, captured CO2 often contains impurities which affect the leakage behavior of CO2. This paper presents a method for continuous and quantitative measurements of CO2 leakage flowrate and the volume fraction of impurities by combining data-driven models with acoustic emission (AE) and temperature sensors. Three data-driven models based on artificial neural network (ANN), random forest (RF), and least squares support vector machine (LS-SVM) algorithms are established. The outputs from the three data-driven models are then integrated to give improved results. Experimental work was conducted on a purpose-built CO2 leakage test rig under a range of conditions. N2 was injected to the CO2 gas stream as an impurity medium. Results show that the integrated model yields a relative error within ±4.0 % for leakage flowrate and ±3.4 % for volume fraction of N2.

Leakage flow mixing in shrouded axial turbines and its control strategies using casing optimization

The geometry of the shroud cavity, which accommodates the rotor shroud leakage flow, is very important due to its impact on the leakage flow path as well as the interaction between the leakage flow and mainstream. The research in this paper numerically investigates the potential for reducing the leakage loss by optimization to the casing. The spatial loss audit and the loss breakdown based on loss mechanisms undertaken in the first part of this study are the foundation to develop promising strategies for minimizing the leakage loss. The profiled casing in the exit cavity effectively deflects the leakage jet into the axial direction when it re-enters the mainstream. The mixing loss is significantly reduced due to the notable decrease in axial velocity disparity of the two streams. On this basis, the exit and inlet cavity are further shaped to both form a step. Reductions in the shroud leakage loss are achieved by alleviating the flow nonuniformity in the exit cavity and reducing the leakage flow rate, respectively. The work in this study contributes to the refinement of control methods for the shroud leakage loss.

Investigation on the effect of different groove depth and width on the tip clearance leakage flow of hydrofoil

Abstract Due to the complexity of axial-flow hydraulic machinery structure and the difficulty of flow field analysis, this paper takes three-dimensional hydrofoil as the research object to analyse the flow characteristics of clearance flow and carry out research on clearance leakage control. The 3-D hydrofoil model with two kinds of gap widths was calculated by using the numerical model method, and compared with the experiment; the influence law of different groove depth and width on the gap leakage flow characteristics and energy characteristics was studied. The results show that with the increase of groove depth, the clearance leakage increases, the lift-drag ratio decreases, and the pressure coefficient increases. Higher axial velocity is shown with increasing groove depth under the small tip clearance, while the opposite is true for large gaps. The optimal groove depth is determined to be D=1mm. When the groove width is 2mm, the pressure coefficient of the hydrofoil is the highest and the vorticity coefficient is the smallest, so the hydrofoil has better performance. In summary, when groove depth D=1mm and groove width W=2mm, the clearance leakage flow rate is smaller and the lift-drag ratio is higher. This study provides a new method for improving the flow field and running stability of turbine-machines with tip clearance in practical engineering.

The effect of rail crown film hole injection angle and blowing ratio on the flow and cooling performance of the squealer tip in a turbine blade

Squealer tip is considered as an efficient and reliable tip geometry design in leakage loss control and thermal load reduction in heavy-duty gas turbine blade. The cooling and aerodynamic characteristics of a squealer tip with different film hole parameters are investigated after validating the numerical approach. Firstly, superior aerodynamic and cooling performance of the rail crown film hole (RCFH) scheme is proved by comparing three squealer tip structures. Subsequently, two kinds of injection angles (streamwise injection α and normal injection β) and three angle values (35°, 90°, and 145°) are studied in RCFH schemes. Finally, a compound angle scheme consisting of optimal α and β is investigated at blowing ratios (M) varying from 0.5 to 2.0. In varied α hole schemes, the velocity of the coolant can be divided into the radial and streamwise components, the effects of which on leakage control are complementary, leading to minimal sensitivity of total leakage flow rate (LFR) to α. Increasing and decreasing α can both enhance the coolant attachment on the rail crown surface compared with the radial injected scheme. In varied β hole schemes, more coolant momentum is used to resist the leakage flow as β increases, which results in remarkable LFR reduction. Moreover, the back-press effect of leakage flow on the coolant is markedly enhanced, improving the utilization of coolant. In compound angle scheme, increasing M leads to enhanced impingement on clearance flow, and the maximum values of average film cooling efficiency (η) on the rail crown and cavity floor appear at M = 1.0 and M = 1.5, respectively.

Turbomachines seal flow resistance enhancement and leakage reduction based on flow control method with bow-shaped auxiliary teeth

Improving sealing performance without clearance reduction is important for the economic and safety operation of modern turbomachines. For this purpose, this study proposes the bow-shaped auxiliary teeth to reduce the leakage. One bow-shaped auxiliary tooth is installed after each seal tooth to guide the leakage jet towards the side wall of seal tooth. Then the leakage jet attaches itself to the inner wall of cavity. The Computational Fluid Dynamics method is used to calculate the flow field in the new seal. Results show that flow impingements, flow deflections, and enhanced vena contraction effect increase the leakage flow resistance and reduce the leakage velocity. The application of the bow-shaped auxiliary teeth reduces the leakage flow rate by 43.8–46.3 % compared with the labyrinth seal. Geometry parameters analysis shows that reducing the axial distance between seal tooth and bow-shaped auxiliary tooth, and increasing the central angle of bow-shaped auxiliary tooth are beneficial for leakage reduction. With the increase in the radius of bow-shaped auxiliary tooth, the leakage firstly decreases and then changes a little.

Flow Field Analysis and Performance Study of a Hydrogen Circulation Pump for Proten Exchange Membrane Fuel Cell Vehicles with Different Working Clearances

This study investigates the impact of working clearances on the internal flow field, pressure pulsations, flow pulsations, and radial forces experienced by a hydrogen circulation pump. Numerical calculations are conducted on seven sets of distinct working clearances for the pump. The research findings demonstrate that an increase in meshing clearance and radial clearance results in higher leakage flow rate during the compression exhaust process, leading to a decrease in hydrogen circulation pump's exhaust flow rate. When the meshing clearance increases from 0.15 to 0.21 mm, the actual exhaust flow rate of the pump decreases from 37.46 to 32.73 m3 h−1. Similarly, when the radial clearance increases from 0.18 to 0.24 mm, the actual exhaust flow rate of the pump decreases from 42.46 to 29.71 m3 h−1. Additionally, with an increase in meshing clearance, both the radial forces Fx and Fy of the active rotor exhibit a downward trend. Yet, as radial clearance grows, the radial force Fx slightly descends, while the change trend of radial force Fy is first positive decrease and then reverse increase.

Leakage characteristics of plug flow in the case of pipe leakage

AbstractIn order to study the changes in two‐phase flow parameters after pipeline damage and the impact of gas injection on water leakage from damaged pipelines, experimental and simulation studies were conducted on the damaged pipelines. The main objective is to compare the void fraction in intact and damaged states and to investigate the factors influencing and variations in gas–liquid leakage flow rates. The results show that increasing the liquid superficial velocity can reduce the difference in void fraction distribution caused by different damage directions. The leakage flow rate is affected by the direction of damage and the superficial velocity of the respective phase. It has been discovered that gas injection in the pipeline can make it easier to find small‐area pipeline damage. The change rate of the volume void fraction shows different changes with the increase in gas proportion in different directions; the shape of the bubble has no bearing on this change.