Leakage Flow Rate Research Articles

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.

A study of angle parametric optimization of the composite honeycomb on turbine blade tip

To reduce the secondary flow loss of the high-pressure turbine caused by the tip leakage flow, the design of the composite honeycomb tip has been experimentally and numerically examined in this study. The arrangement angle of the composite honeycomb is defined and optimized using the radial basis function and genetic algorithm. The tip flow field of the high-pressure turbine blade with a 2.128 mm clearance is simulated by CFX 18.0, and the arrangement angle of the composite honeycomb is optimized to obtain a lower loss. Moreover, the flat tip, basic honeycomb tip, and optimized honeycomb tip are tested in a low-speed cascade test facility. The results show that the vortices and radial velocity induced by the honeycomb structure cavity increase the kinetic energy loss of the leakage flow and reduce the leakage flow rate. Compared with the basic honeycomb, the optimized honeycomb has a supplemental blocking effect on the tip leakage flow by reducing the crosswise pressure gradient in the blade tip. The optimized honeycomb also changes the outlet angle of the leakage flow in the tip clearance, reduces the leakage vortex, and the total pressure loss is further reduced by 2.5%.

Analysis of Fluid-Solid coupling heat transfer characteristics of hydrogen circulating pump

The hydrogen circulating pump (HCP) is in a high-temperature state during operation due to the heat generated by the pressure change of the transported gas. The current research on the flow characteristics of the HCP has not taken into account the influence of internal heat transfer factors, resulting in significant errors between the research results and actual test results. In this article, we define the contact modes of the fluid–solid interfaces based on heat transfer theory, propose a step-by-step calculation method based on different time scales, and complete the simulation of the fluid–solid coupling model. Compared with the test flow rate of 15.44 g/s, the fluid–solid coupling model considering heat transfer factors calculated a flow rate of 15.15 g/s with an error of only 1.85 %, while the single fluid model without considering heat transfer effects calculated a value of 14.67 g/s with an error of 5.0 %. Analyzing the internal mechanism of heat transfer leading to an increase in simulated flow rate, the external surface heat dissipation and internal heat conduction on one hand lead to a decrease in gap leakage flow rate, thereby reducing leakage volume, and on the other hand, increase the density of gas transported in the rotor cavity area, thereby improving the conveying capacity. The calculation method proposed in this article solves the problem of the large time difference between instantaneous fluid flow and slow heat transfer, shortens the calculation time, has higher calculation accuracy, and plays an important role in the precise design process of HCPs.

Experimental Investigation of Leakage Flow Rate and Fluidisation beneath Polyethylene Pipes in Non-Uniform Soils

Soil fluidisation around buried pipes is one of the water leakage effects that has a direct influence on the ultimate failure of pipelines. In this research, using a laboratory model, the fluidisation caused by water leakage from three cracks with three lengths (14, 17, and 20 mm) and a 3 mm diameter hole for five pressures (1.5–5.5 bar) in non-uniform soils has been evaluated. The experiments were carried out both for pipes buried in soil, as well as exposed pipes. In the buried pipe tests, leakage flow rate, fluidisation, and mobile bed zone dimensions were investigated. The results showed that the increase in leakage flow rate due to an increase in pressure and crack length in exposed pipes is higher than in buried pipes. The exponent of the leakage–pressure relationship was obtained between 0.40 and 0.47 for the hole and between 0.8 and 1.9 in the crack. Observing different development patterns for fluidisation and mobile bed zones in cracks and holes, new relationships are presented for the height, width, and cross-sectional area of the leakage zones.

Prediction of small-scale leak flow rate in LOCA situations using bidirectional GRU

It is difficult to detect a small-scale leakage in a nuclear power plant (NPP) quickly and take appropriate action. Delaying these procedures can have adverse effects on NPPs. In this paper, we propose leak flow rate prediction using the bidirectional gated recurrent unit (Bi-GRU) method to detect leakage quickly and accurately in small-scale leakage situations because large-scale leak rates are known to be predicted accurately. The data were acquired by simulating small loss-of-coolant accidents (LOCA) or small-scale leakage situations using the modular accident analysis program (MAAP) code. In addition, to improve prediction performance, data were collected by distinguishing the break sizes in more detail. In addition, the prediction accuracy was improved by performing both LOCA diagnosis and leak flow rate prediction in small LOCA situations. The prediction model developed using the Bi-GRU showed a superior prediction performance compared with other artificial intelligence methods. Accordingly, the accurate and effective prediction model for small-scale leakage situations proposed herein is expected to support operators in decision-making and taking actions.

Influence of air changes per hour on hydrogen leaks in mechanically ventilated enclosures

The integration of hydrogen energy systems into nearly zero-emission buildings (nZEB) is emerging as a viable strategy to curtail greenhouse gas emissions associated with energy use in these buildings. However, the indoor or outdoor placement of certain hydrogen system components or equipment necessitates stringent safety measures, particularly in confined environments. This study aims to investigate the dynamics of hydrogen dispersion within an enclosure featuring forced ventilation, analyzing the interplay between leakage flow rates and ventilation efficiency both experimentally and numerically. To simulate hydrogen's behavior, helium gas, which shares similar physical characteristics with hydrogen, was utilized in experiments conducted at leakage flows of 4, 8, and 10 L/min, alongside a ventilation rate of 30 air changes per hour (ACH). The experiments revealed that, irrespective of the leakage rate, the oxygen concentration returned to its initial level approximately 11 min post-leakage at a ventilation rate of 30 ACH. This study also encompasses a numerical analysis to validate the experimental findings and assess the congruence between helium and hydrogen behaviors. Additionally, the impact of varying ACH rates (30, 45, 60, 75) on the concentrations of oxygen and hydrogen was quantified through numerical analysis for different hydrogen leakage rates (4, 8, 10, 20 L/min). The insights derived from this research offer valuable guidance for building facility engineers on designing ventilation systems that ensure hydrogen and oxygen concentrations remain within safe limits in hydrogen-utilizing indoor environments.

Experimental study on flow characteristics and burning behavior for fire of flammable gases leakage underwater

The occurrence of subsea pipeline leakage incidents has gradually increased with the rapid development of the offshore oil and gas industry. Research on the fire dynamics of flammable gases leakage underwater is very limited, particularly in understanding the coupling mechanism of flow and combustion on the water surface. This paper presents a systematical investigation on flow characteristics and burning behavior for fire of flammable gases leakage underwater. A series of laboratory-scale fire behavior experiments were conducted through a self-designed experimental platform, consisting of the leakage control module, water tank and measurement apparatus. It was revealed that the leakage flow rate and water depth would influence the flow characteristics and burning behavior significantly. Two different burning conditions were found for the flame burning above the water surface (FBWS), i.e., the stable and self-extinguishing (unstable) burning states. The dimensionless analysis is conducted for the burning conditions, where the critical criterion is developed to distinguish the stable and unstable burning states. The base diameter of stable FBWS is almost 1.6 times of the diameter of bubble plume on the water surface. The flame pulsation frequency and dimensionless flame height (the ratio of height to base diameter of flame) of the stable FBWS are different from thoes of liquid pool fires and gas diffusion fires. Consequently, a correlation between the Strouhal number and the Froude number is correlated. Finally, the correlation between the dimensionless flame height and the dimensionless heat release rate is proposed for the stable FBWS.

Numerical study of a novel cooling protection scheme with rail crown holes for the squealer tip in a turbine blade

The squealer tip is acknowledged as an effective and dependable design for minimizing leakage loss and reducing thermal load in high-pressure turbine blades. After confirming the numerical approach, this study explored the cooling and aerodynamic characteristics of a novel cooling protection scheme with rail crown holes in a squealer tip. The rail crown hole parameters including the hole number, size, and distribution are research variable. Evaluation indexes of cooling and aerodynamic performance are the tip surface adiabatic film cooling efficiency (η) and clearance leakage flow rate (LFR). In cooling aspects, increasing the hole number or the hole size can improve the coolant attachment to the rail crown surface under the same coolant mass flow rate (Q). The coolant distribution within the cavity is substantially improved by concentrating the film holes at the leading-edge rail, which enhances the cooling protection of the cavity floor. In aerodynamic aspects, at low Q conditions, the total LFR correlates only with Q and is less sensitive to hole parameters. At high Q conditions, enlarging the hole size proves more effective in suppressing total LFR. Additionally, three cases with optimal cooling effects are chosen to investigate the impact of Q. These three cases are the scheme with an increasing hole number (case 1), the scheme with an enlarging hole size (case 4), and the scheme with concentrated holes at the leading edge (case 5). The results show that case 5 consistently exhibits superior cooling protection for the cavity floor in all Q conditions. For average η of the rail crown surface, cases 1 and 5 reach the peak value of average η at Q = 1.0Q0, while case 4 attains its peak value at Q = 1.5Q0.

Aerothermal performance of cavity tip with flow structure effects in a transonic high-pressure turbine blade

Understanding the mechanisms of leakage flow control and heat load distribution is important in optimizing the structure of cavity tips in gas turbines. This paper investigates the aerothermal performance of cavity tip in a transonic high-pressure turbine stage. By analyzing flow structure, the effects of squealer height, squealer width and gap height on aerothermal performance are explained. It has been found that both the leakage flow and heat load distribution are influenced by the structure of vortices in the cavity. The leakage flow is controlled by the suction-side cavity vortex and the scraping vortex. The heat load distribution relates to the “M-shaped” leakage flow induced by the scraping vortex. The geometric parameters can affect the structure of vortices, which then impacts the aerothermal performance of cavity tip. As the squealer height is 2.5τ0, both the leakage flow rate and average heat transfer coefficient decrease by 0.64 % and 6.6 %, respectively. A multi-objective optimization with a feedforward neural network prediction is conducted to determine the distribution characteristics of optimal design parameters. The optimal values are approximately 2.34 for the expansion ratio, 0.5τ0 for the squealer width and 0.5τ0 for the gap height. The optimal squealer height ranges from 1.5τ0 to 2.5τ0.

On the Aero-Thermal Performance of Rim Film Cooling in the Squealer Tip of a Linear Turbine Cascade

Abstract The present study proposes a novel rim film cooling design, motivated by the fact that the suction-side rim and the cavity floor near the leading edge of a conventional squealer tip with a camber-line film hole array are directly subjected to high-temperature gas. The new design consists of cooling injection for rim-hole or -slot cooling at the leading edge. The parameters of injection geometry and cavity depth are also discussed in this study. The flow physics, leakage flowrate, heat transfer characteristics, and vortices in the cavity are carefully analyzed. The results show that rim film cooling can substantially inhibit tip heat transfer and the amount of hot leakage flow. Compared with the typical design, the maximum and average heat transfer coefficients of the blade tip of the rim slot case are reduced by 12.83% and 5.43%,, respectively. The variation in cavity depth is sensitive to the heat transfer on the cavity floor of the squealer tip blade. With the optimal design, the average and maximum heat transfer coefficients are reduced by 14.42% and 14.21%,, respectively. In addition, the leakage flowrate can be reduced by a maximum of 3.67% by rim injection compared with the conventional squealer tip.

A mathematical model for accurately predicting face mask wearer’s inhalation exposure to self-exhaled and external pollutants

Face masks reduce the wearers’ inhalation exposure to external pollutants, but intensifying the exposure to their self-exhaled pollutants. To quantify the wearers’ inhalation exposure to the two sources of pollutants, a mathematical model for transient-state conditions was firstly established and scientifically validated, with an average relative deviation of only 3 % from the experimental data and only 6 % from the validated CFD simulated results. Proportion of leakage flow rate via gap (γ) was mainly affected by breathing flow rate (Lexh/inh) and gap’s area (Sg), followed by face mask’s surface area (Sm) and thickness (Mm). The 7 L/min of Lexh/inh led to the maximum inhalation fraction (IF) of self-exhaled pollutants at about 54 %, implying that wearing face masks poses a threat to the wearer’s health. When face mask’s volume increased from 50 mL to 150 mL, the relative intake dose (ID∗) of external pollutants decreased by 0.12 but the IF of self-exhaled pollutants increased by 9 %. When face mask’s filtration efficiency increased from 10 % to 90 %, the IF of self-exhaled pollutants and the ID∗¯ of external pollutants decreased by 13 % and 0.23, respectively. The increase of 0.80 in γ decreased the IF of self-exhaled pollutants by 8 % but increased ID∗¯ of external pollutants by 0.19, implying that protective performance always contradicts on the inhalation exposure to self-exhaled pollutants. The model established provides a new method to evaluate the performance of face masks rapidly and accurately, and further benefits the improvement of face masks and even other respiratory protective equipment.

Measuring micro-sized leakage channel flow in macro-sized machines

In fluid machines, micro-sized clearances between a rotating shaft and a static casing give rise to leakage-flow losses. The moving boundary layer makes models non-trivial and complex to analyse. This study proposes a method to measure the leakage flow as a function of the channel width and rotational speed. The experimental setup consists of a rotating shaft enveloped by a cylindrical stator equipped with two micro-range actuators. Pressurised air, fed through the stator, induces a flow through two channels adjustable from 20 to 100 μm. At channel widths of 20 μm and 2 bar air pressure, the flow rate reduced by 25% at 9000 rpm compared to non-rotating, this speed-dependency was not measured above 4 bar. The actuators facilitated the assembly and enabled measurements of the speed and channel-size dependency of the leakage flow rate. The proposed methods and actuators can be extended to analyse more complex rotary-fluid machines.

Quantifying the heat transfer effect of the axial turbine stator well cavity

A Thermal-Fluid-Structural model is presented for quantifying the heat generation by the labyrinth seal in the low-pressure turbine stator well cavity. The method combines windage heating and convective heat transfer effects for labyrinth seal design, making it possible to use the heat transfer boundary condition instead of adiabatic to do the computational fluid dynamic calculation. The solutions illustrate how the outlet total temperature may change depending on the seal pressure ratios, windage heating, and heat transfer coefficient. It is further demonstrated that with a fixed seal pressure ratio, the thermal boundary condition has little influence on the leakage flow rate of the seal. The total temperature rise is dependent on the thermal boundary conditions, including the stator/rotor wall temperature, heat transfer coefficient, and windage heat caused by air friction.

Clinical and technical factors in endoscopic skull base surgery associated with reconstructive success.

In this study, we identified key discrete clinical and technical factors that may correlate with primary reconstructive success in endoscopic skull base surgery (ESBS). ESBS cases with intraoperative cerebrospinal fluid (CSF) leaks at four tertiary academic rhinology programs were retrospectively reviewed. Logistic regression identified factors associated with surgical outcomes by defect subsite (anterior cranial fossa [ACF], suprasellar [SS], purely sellar, posterior cranial fossa [PCF]). Of 706 patients (50.4% female), 61.9% had pituitary adenomas, 73.4% had sellar or SS defects, and 20.5% had high-flow intraoperative CSF leaks. The postoperative CSF leak rate was 7.8%. Larger defect size predicted ACF postoperative leaks; use of rigid reconstruction and older age protected against sellar postoperative leaks; and use of dural sealants compared to fibrin glue protected against PCF postoperative leaks. SS postoperative leaks occurred less frequently with the use of dural onlay. Body-mass index, intraoperative CSF leak flow rate, and the use of lumbar drain were not significantly associated with postoperative CSF leak. Meningitis was associated with larger tumors in ACF defects, nondissolvable nasal packing in SS defects, and high-flow intraoperative leaks in PCF defects. Sinus infections were more common in sellar defects with synthetic grafts and nondissolvable nasal packing. Depending on defect subsite, reconstructive success following ESBS may be influenced by factors, such as age, defect size, and the use of rigid reconstruction, dural onlay, and tissue sealants.

Research on Deep learning based Ultrasonic Image Learning to Develop a Gas Leak Detection Model

If a gas leak occurs in an industrial area, identifying the location of the gas leak and predicting the scale of the accident are challenging owing to the invisible nature of the gas. In this study, we developed a deep learning-based gas leak detection model that can obtain not only the gas leak status, but also the gas leak location and flow rate information, by using technology to visualize the ultrasonic waves generated during gas leaks. Research methods are broadly categorized into data collection and model learning methods. First, data was collected using an ultrasonic camera to capture ultrasonic images at different measurement distances (1 and 3 m) and gas leak flow rates (0-8 L/min). YOLO (You Only Look Once) was used for image learning, and the model was trained after setting the class according to the gas-leak flow range. The clarity of the collected ultrasonic images decreased as the measurement distance increased. In addition, there was little difference between the images for each leakage flow rate, posing challenges in distinguishing them with the naked eye. However, the model learning results showed high accuracy, with a precision of 0.960, recall of 0.967, and mAP (IoU (Intersection over Union) 50%) of 0.987. Applying this model as a gas safety management technology at industrial sites, enables the accurate determination of gas leak status, gas leak location, and gas leakage flow. This information is expected to guide appropriate accident responses for workers.

Numerical Modeling and Simulation of a Poroelastic Journal Bearing Lubricated By Nanofluids with Couple-Stresses

In this paper we present a numerical simulation of a porous journal bearing considering the fluid film – poroelastic matrix interaction and the non-Newtonian rheological behavior of nanolubricant consisting of base fluid and nanoparticles (NPs). The flow of nanolubricant in the bearing clearance space is described by the Vijay Kumar Stokes micro-continuum theory which considers the characteristic size of nanoparticles such as fullerenes dispersed in a base oil. The flow of the nanolubricant in the porous medium is modeled by the modified Darcy’s law where the Beavers–Joseph slip conditions are applied at the fluid film-porous matrix interface. The deformation of the fluid-film porous matrix interface due to hydrodynamic pressure is calculated by using a simplified analytical thin elastic liner model. The hydrodynamic behavior of lubricating film is governed by the modified Reynolds equation obtained from the momentum, moment of momentum, and mass conservation laws using the classical Reynolds derivation process. The bearing porosity is introduced into the governing modified Reynolds equation by means of the Morgan-Cameron approximation. The steady-state analysis shows that for an imposed operating eccentricity, the load capacity increases with the characteristic size and the concentration of NPs while the attitude angle, the leakage flow rate, and the coefficient of friction decrease. On the other hand, the permeability decreases the hydrodynamic pressure, the load capacity, and the leakage flow rate, and increases the attitude angle and the coefficient of friction.

A fluidic oscillator seal concept for sealing performance enhancement by controlling the kinetic energy carry-over effect

Annular gas seals are critical components in turbomachines for restricting leakage and ensuring efficiency. However, their sealing performance is significantly affected by the kinetic energy carry-over (KEC) effect. In this paper, a novel concept of the fluidic oscillator seal (FOS) is proposed. The self-oscillating flow pattern inside FOS controls the undesired KEC effect, thus enhancing the sealing performance. The effectiveness of FOS is evaluated by comparing with the cutting-edge air curtain technology (ACT). Comparison results show that FOS exhibits superior sealing performance under all the studied operation conditions. Its superiority becomes more prominent as the seal clearance and teeth number increase. The maximum discharge coefficient reduction ratio reaches up to 51.4%, over 4 times larger than ACT. Moreover, the FOS requires only about half the installation space for an equivalent leakage flow rate compared to the ACT.