Tip Section Research Articles

RESEARCH OF STRESS-STRAIN STATE OF ORE GRINDING MILLS

Over the past decades, computing complexes based on finite element methods, such as "MARS," "Lira," "ASKA," "ADINA," "COSMOS," "ANSYS," etc., have been developed and are now successfully operational. However, alongside the development of powerful universal computing packages for various applications, there is a growing trend towards specialized complexes tailored to solve specific practical problems. This trend is driven by the advancement of automation systems for designing both typical structures and computer codes. In this paper, we address the problem of determining displacements and stresses in ore-grinding mills under asymmetric loading, based on a developed methodology and a specialized program for calculating the shells of revolution. Ore-grinding mills are complex structures resembling stacked branched shells of revolution supported by fins. The methods for calculating such structures, considering meridian edges, in accordance with the theory of constructive-orthotropic shells, are well-developed. While the calculation schemes of general-purpose program packages account for the self-weight of the drum, the weight of the ball loading, and the reaction of the supports, our specialized program additionally considers centrifugal forces of the drum, pulp, and inwall. It also accounts for the branching of the drum meridian and the possibility of the tip resting on one or two bearings, positioned at an angle φ in the tip section. These structures are loaded with their own weight, the weight of the inwall in the form of armored plates, as well as the weight of the ore, which, when mixed with water, is crushed by metal layers or rods located in a cylindrical drum. The crushing of ore occurs due to the rotation of the structure, which is horizontally positioned and supported by sliding bearings. This necessitates accounting for the centrifugal forces of the specified masses, as well as reactions from the bearings. Detailed description of load calculation and their representation by Fourier series is provided, along with a comprehensive consideration of taking rigid shifts into account when calculating the structural strength. The results of the study on the stress-strain state and strength of ore grinding mills are presented comprehensively.

Influence of manufacturing errors on the aerodynamic working stability of axial flow compressors

In turbomachinery, manufacturing errors in blades have been found to impact aerodynamic performance. This paper aims to investigate the effect of manufacturing errors on the stability of compressor operation. To this end, a geometric uncertainty reduced-order model is developed to generate the normal profile error of rotor blades based on specific tolerances, considering the simultaneous variation of blade parameters during manufacturing. The stability margin improvement of the compressor is then calculated using computational fluid dynamics (CFD), and a neural network is employed to predict the relationship between the uncertainty input variables and the stability margin improvement. Finally, a large number of samples are generated using the Quasi-Monte Carlo method, and Sobol sensitivity analysis is performed. According to the results, manufacturing errors can reduce the stability margin by an average of 0.9% and up to 3% in the limiting case. The parameters that have the greatest impact on the stability of the compressor are the blade chord length of the hub section and the maximum thickness of the tip section. These two parameters affect blade tip blockage by influencing spanwise secondary flow on the suction surface. Additionally, the decrease in maximum thickness at the tip section affects the separation of the boundary layers on the suction surface, resulting in additional effects.

Comprehensive study of vortices interaction and blades height effect in a Darrieus vertical axis wind turbine with J‐type blades

AbstractThere is a growing demand to improve the performance of vertical axis wind turbines to facilitate their commercialization for application in urban areas. This study utilizes a 3D numerical analysis to examine the influence of different vortices generated on turbine efficiency with straight and J‐type blades. The numerical simulation of this study employs the Reynolds‐Averaged Navier–Stokes equations and ‎sliding ‎mesh techniques ‎to more accurately model the rotational motion of blades about the turbine axis in relation to the ‎wind. Comparing the output ‎torque and the flow field at different span‐wise sections, the J‐type blades achieve better ‎performance at mid‐spans where the effect of stall vortices is dominant. Conversely, the lower ‎performance of J‐type blades is seen at tip spans due to stronger tip vortices. Investigations also ‎reveal the criticality of the downwind region on the overall performance at high tip speed ratios. It is observed that by ‎increasing the height, the tip vortices are limited to the tip sections, and stall vortices expand further ‎along the blade. At TSR = 1, the improvement by J‐type blades rises from 10% at a height of 0.8 m to 44% ‎at 3 m. The growth in height at lower wind speeds becomes more beneficial. Compared to the straight blades, the self‐starting ‎generated torque by J‐type blades for heights of 0.8, 1.2, and 1.6 m, are improved by 15.6%, ‎‎26.9%, and 34.7%, respectively. Overall, it is concluded that by increasing the blade height, the superiority ‎of the J‐type blade becomes more noticeable as the blade mainly contributes to suppressing the stall ‎vortices effect where the tip vortices effect is not presented. ‎

Impact of Atomic Vacancy Defects on Vibrational Characteristics of Chiral MWCNT for Viruses/Bacteria

In this study the authors investigated the vibrations performance of chiral multi-walled carbon nanotubes (MWCNTs). They examined chiral MWCNTs with attached bacteria positioned at both the tip and middle sections of the nanotubes. The main goal of this research was to create a sensor with the ability to detect and distinguish bacteria or viruses that could potentially adhere to the surfaces of chiral MWCNTs. The authors considered two boundary conditions, fixed-fixed and fixed -free for the chiral MWCNT. They utilized a molecular structural mechanics approach. In this approach the vibrational responses of chiral MWCNT-based nano-biosensors with different diameters of the chiral MWCNTs were examined. The study’s objective was to fill research gaps by introducing an innovative approach for detecting defects in chiral MWCNTs through vibrational analysis. They simulated 432 MWCNT samples to investigate the vibrational performance of defective chiral MWCNTs. The results suggested that the first mode of the vibrational frequency of the chiral MWCNT is particularly significant for sensing applications. It was observed that as the percentage of vacancy defects increased, the natural frequency decreased for both boundary conditions.

Clinical characteristics and follow-up analysis of 63 cases of silicosis complicated with cavity-pulmonary tuberculosis

Objective: To investigate the clinical characteristics and prognosis of silicosis complicated with cavity-pulmonary tuberculosis. Methods: The clinical data of 63 patients with silicosis complicated with cavity-pulmonary tuberculosis (group A) and silicosis patients (group B) admitted to Yantaishan Hospital from July 2018 to July 2022 were collected and analyzed. Results: Patients in group A were all male, and the common symptoms were cough, expectoration, chest tightness, shortness of breath, and hemoptysis. CT cavity lesions involving the lung, often occurs in the lung after the tip section, after the back section and basal segment, thick-walled cavity, may be accompanied by satellite lesions, endobronchial spread focal, pneumothorax, pleural effusion, etc. 1225 cases of group B patients haemoptysis of 59 patients, cavity in 3 patients, haemoptysis and/or cavity rate was lower than that in group A, the difference was statistically significant (P<0.05) . In group A, CT reexamination 6-24 months after anti-tuberculosis treatment showed that 52 cases (82.5%) had cavity reduction/healing, 8 cases (12.7%) had recurrence, and 3 cases (4.8%) had damaged lung (2 died) . Conclusion: Silicosis patients with hemoptysis and/or CT in cavity should be more vigilant about combined tuberculosis, anti-tuberculosis treatment and/or dynamic CT follow-up helps laboratory diagnosis negative patients.

In vitro propagation and DNA barcoding of the rare near endemic Plantago sinaica (Barnéoud) plant in Saint Katherine, Sinai

Plantago sinaica is a rare perennial shrub near-endemic to Egypt and found in Saint Katherine Protectorate in Sinai. The first successful in vitro propagation protocol was conducted to protect the plant outside its natural reserves. Shoot tip, stem node section, cotyledonary node, and root explants separated from in vitro germinated seedlings were cultured in vitro on Murashige and Skoog (MS) medium enriched with different concentrations and types of cytokinins. It was found that 6-benzyl adenine (BA) is the most efficient cytokinin. MS medium containing 3.33 µM BA and 0.54 µM α-naphthalene acetic acids (NAA) produced 10.25 and 11.30 shoots/explant using shoot tip and stem node section, respectively. Conversely, MS medium + 2.22 µM BA + 0.54 µM NAA produced 13.25 shoots from root explants. Surprisingly, the cotyledonary node explants favored MS medium free from plant growth regulators (PGRs), which produced only 4.25 shoots/explant. The multiplied shoots were rooted successfully with a 100% rooting percentage on half MS medium containing 1.23 or 2.46 µM indole-3-butyric acid (IBA). In vitro, rooted plantlets were efficiently transferred to the greenhouse with a 90% survivability. Finally, the plant was identified using three DNA barcodes; 1,5-bisphosphate carboxylase/oxygenase large subunit (rbcL), plastid photosystem II protein D1 intergenic spacer region (psbA–trnH), and Internal Transcribed Spacer (ITS) barcodes. Additionally, psbA–trnH and ITS were novel and submitted to the GenBank databases for the first time for Plantago sinaica. Our study supports the United Nations Sustainable Development Goal number 15, which is to preserve, restore and reinstate sustainable usage of terrestrial ecosystems and to stop biodiversity loss.

Optimisation of proprotors for tilt-wing eVTOL aircraft

Proprotors for tilt-wing advanced air mobility aircraft are often optimised without considering the transition from hover to cruise. This paper presents an optimisation method, which considers transition flight phases. Proprotors are optimised for a multi-rotor tilt-wing vehicle at nominal cruise, transition, and hover conditions. Results show that proprotors designed with transition flight conditions tend to have smaller chord distributions along the span than those designed without considering transition. The blade twist from root to tip of the transition proprotors is also more extreme, and a slight increase in pitch towards the tip section of the propeller is observed. The more significant overall twist avoids retreating blade stall during transition and transition power is the most sensitive to the pitch angle at the mid-radius to tip section of the blade. However, a proprotor that is designed taking transition into account requires a hover power that is 5.6% larger than a proprotor designed for cruise and hover only. Pareto-optimal proprotor designs from an optimisation case without transition cannot deliver enough thrust throughout all transition flight phases.

Study on fatigue crack propagation failure in semi-rigid base

Nowadays, it is of non-negligible importance to extend the service life of in-service pavements. As the base form, shrinkage fractures and plate faults are the main reasons for the failure of semi-rigid base and it is of practical significance to study the cracking mechanism of the fracture damage from the microscopic point of view. In order to obtain the fatigue propagation law of the cracks inside the semi-rigid base, a three-dimensional preset depth crack fatigue propagation model was established based on the finite element quasi-static method and ground-penetrating radar detection data, and monitors the propagation of the crack tip section through the probe, obtaining the number of load actions and the crack propagation depth during the destabilization. Subsequently, this paper investigates the stress field distribution and fatigue propagation failure law of crack tip section inside the semi-rigid base based on the ensemble analysis method of stress intensity factor, combined with the macroscopic modulus change of the base structure. The propagation form of single-crack cracks within the base layer is mainly dominated by type I (opening type) cracks, but there are also the remaining two crack propagation trends at the tip. The analysis shows that the smaller the modulus of the semi-rigid base, the less likely the crack is to undergo an initial tip change. In the case of four preset depths, the preset depth of 50 mm is the most vulnerable to crack tip change. Relatively speaking, and the 200 mm preset depth cracks expand the maximum depth when the structure fails in all preset depths. It can be seen from the experiments that the strain field at the crack tip of 50 mm presetting depth is stronger. The strength of stress and strain fields near the crack tip at 200 mm and 150 mm preset depths is mainly related to the modulus of the base layer. The larger the modulus, the stronger the stress and strain fields. The distribution of the field strength at the crack tip of 100 mm and 50 mm presetting depth is less affected by the base layer modulus. In this study, the three-dimensional simulation of the fatigue action of the internal cracks in the semi-rigid base is innovatively proposed, which helps to clarify the distribution of the stress field and the fatigue failure of the internal crack tip of the semi-rigid base, and provides a new way of thinking for the assessment of the service performance of the long-life pavements and the failure mechanism of the microscopic damages.

Prevention of urinary tract infection using a silver alloy hydrogel-coated catheter in critically ill patients: A single-center prospective randomized controlled study

BackgroundA new type of silver alloy hydrogel-coated (SAH) catheter has been shown to prevent bacterial adhesion and colonization by generating a microcurrent, and to block the retrograde infection pathway. However, these have only been confirmed in ordinary patients. This study aims to evaluate the effectiveness of a SAH catheter for preventing urinary tract infections in critically ill patients. MethodsThis was a prospective single-center, single-blind, randomized, controlled study. A total of 132 patients requiring indwelling catheterization in the intensive care unit (ICU) of the First Affiliated Hospital of the University of Science and Technology of China between October 2022 and February 2023 and who met the study inclusion/exclusion criteria were randomly divided into two groups. Patients in the SAH catheter group received a SAH catheter, while patients in the conventional catheter group received a conventional siliconized latex Foley catheter. The main outcome measure was the incidence of catheter-associated urinary tract infections (CAUTIs). Secondary outcome indicators included urine positivity for white blood cells and positive urine cultures on 3 days, 7 days, 10 days, and 14 days after catheterization, number of viable bacteria in the catheter biofilm on day 14, pathogenic characteristics of positive urine cultures, length of ICU stay, overall hospital stay, ICU mortality, and 28-day mortality. All the data were compared between the two groups. ResultsA total of 68 patients in the conventional catheter group and 64 patients in the SAH catheter group were included in the study. On day 7 after catheter placement, the positivity rate for urinary white blood cells was significantly higher in the conventional catheter group than in the SAH catheter group (33.8% vs. 15.6%, P=0.016). On day 10, the rates of positive urine cultures (27.9% vs. 10.9%, P=0.014) and CAUTIs (22.1% vs. 7.8%, P=0.023) were significantly higher in the conventional catheter group than in the SAH catheter group. On day 14, the numbers of viable bacteria isolated from the catheter tip ([3.21±1.91]×106 colony-forming units [cfu]/mL vs. [7.44±2.22]×104 cfu/mL, P <0.001), balloon segment ([7.30±1.99]×107 cfu/mL vs. [3.48±2.38]×105 cfu/mL, P <0.001), and tail section ([6.41±2.07]×105 cfu/mL vs. [8.50±1.46]×103 cfu/mL, P <0.001) were significantly higher in the conventional catheter group than in the SAH catheter group. The most common bacteria in the urine of patients in both groups were Escherichia coli (n=13) and Pseudomonas aeruginosa (n=6), with only one case of Candida in each group. There were no significant differences between the two groups in terms of ICU hospitalization time, total hospitalization time, ICU mortality, and 28-day mortality. ConclusionSAH catheters can effectively inhibit the formation of catheter-related bacterial biofilms in critically ill patients and reduce the incidence of CAUTIs, compared with conventional siliconized latex Foley catheters; however, regular replacement of the catheter is still necessary.

A comprehensive multi-objective optimization study for the aerodynamic noise mitigation of a small wind turbine

The noise emitted by small wind turbines is one of the main reasons for their poor public perception for use in urban areas. An optimization study was performed to mitigate the aerodynamic noise of a 750 W turbine through altering the geometry of solid and more importantly hollow blades for the first time. A validated in-house code simultaneously minimizes the aerodynamic noise and maximizes the output power. The inertia of the blades is another important design parameter for small turbines as it influences the starting performance. The minimization of starting time was added to the above-mentioned goals and another optimization was done. The outcomes highlight the great significance of two ends of the blade; the tip section has a key role in alleviation of the noise as well as the improvement of the power coefficient while the root part could speed up the starting. Quantitatively, the optimization of solid blades shows that a 1.9 dB reduction in aerodynamic noise is attainable at the expense of a 1.6% loss in the power coefficient. Compared to solid blades, the aerodynamic noise and the starting time were reduced for hollow ones by 1 dB and 30% respectively. The latter is very attractive for use of small turbines in low-wind areas.

Hardening of bucket teeth made from creusabro 8000 steel by using the induction hardening method

Excavators are often used in mining projects such as for penetrating, excavating, dredging, gouging, and crushing mineral rocks. Bucket teeth are an excavator component that is often being replaced due to failure. The most common failure mode that occurred in bucket teeth was wear on the tip or front section of it. To reduce the wear of the bucket teeth material then its hardness should be increased. As the hardness value increases, the resistance to wear increases. The bucket teeth were made of Creusabro 8000 steel and a hardening process was then carried out on the front section of the bucket teeth components by using an induction furnace. The power used in the induction furnace varies from 28, 35, 42 and 49 kW (kilowatts) and the holding time varies between 3 and 5 minutes. The heat treatment process used oil as a cooling medium. The analysis was carried out to determine the area that experienced an increase in hardness and its occurred microstructure. Microstructure examination was carried out with an optical microscope, and hardness test by using a Vickers microscopy. It can be concluded from the result of the analysis that the large area experienced an hardness increase is directly proportional to the electric current magnitude and holding time. The microstructure has changed from fine pearlite to martensite thus hardness of Bucket Teeth can be increased up to 100% of the initial hardness.

Investigation of ice accretion effect on the aerodynamic characteristics of a wind turbine blade tip after a short icing event

The paper investigates the flow behavior near the NACA 64-618 airfoil profile of the blade tip section of a wind turbine for electric power production after a short icing event. The flow simulation considering the rotation speed of the wind turbine blade is performed to assess the effect of icing on the aerodynamic characteristics. Degradation of aerodynamic characteristics affects the electrical energy production of the wind turbine. The aerodynamic lift and drag coefficients are calculated for different angles of attack. The flow velocity fields near the airfoil are analyzed. The pressure coefficient distributions along the profile surface are obtained. The points of flow stall and changes of aerodynamic characteristics at different angles of attack are determined.

Clinical outcomes of squamous cell carcinomas following complete saucerization with negative margins: Retrospective case series from 2010-2022

Clinical outcomes of squamous cell carcinomas following complete saucerization with negative margins: Retrospective case series from 2010-2022

Boundary layer control for low Reynolds number fan rig testing

Ultra-high bypass ratio turbofans offer significant reductions in fuel and pollution due to their higher propulsive efficiency. Short intakes might lead to a stronger fan-intake interaction, which creates uncertainty in stability at off-design conditions. Due to the prohibitive cost of full-scale experimental testing, subscale testing in wind tunnels is used to understand this behaviour. The low Reynolds number of subscale models results in unrepresentative laminar shock-boundary layer interactions. The boundary layer state thus needs to be conditioned to better represent full-scale transonic fans. This paper proposes the use of an inexpensive and robust flow control method for the suction side of a fan blade. Design guidelines are given for the location and height of the discrete roughness elements used to control the boundary layer state. This paper also presents a rapid experimental validation methodology to ensure and de-risk the application of the boundary layer trip to 3D rig blades. The experimental methodology is applied to a generic aerofoil representative of a fan tip section. The experimental method proves that it is possible to reproduce boundary layers and pressure distributions of a full-scale fan blade on a 1/10 subscale model. The results obtained confirm that the boundary layer trip method successfully promotes transition at the location representative of full-scale blades, avoiding unrepresentative laminar shock wave boundary layer interactions. This highlights the importance of conditioning boundary layers in low Reynolds number fan rig testing.

Computational fluid dynamics (CFD) modeling of actual eroded wind turbine blades

Abstract. Leading edge erosion (LEE) is one of the most critical degradation mechanisms that occur with wind turbine blades (WTBs), generally starting from the tip section of the blade. A detailed understanding of the LEE process and the impact on aerodynamic performance due to the damaged leading edge (LE) is required to select the most appropriate leading edge protection (LEP) system and optimize blade maintenance. Providing accurate modeling tools is therefore essential. This paper presents a two-part study investigating computational fluid dynamics (CFD) modeling approaches for different orders of magnitudes in erosion damage. The first part details the flow transition modeling for eroded surfaces with roughness on the order of 0.1–0.2 mm, while the second part focuses on a novel study modeling high-resolution scanned LE surfaces from an actual blade with LEE damage on the order of 10–20 mm (approx. 1 % chord); 2D and 3D surface-resolved Reynolds-averaged Navier–Stokes (RANS) CFD models have been applied to investigate wind turbine blade sections in the Reynolds number (Re) range of 3–6 million. From the first part, the calibrated CFD model for modeling flow transition accounting for roughness shows good agreement of the aerodynamic forces for airfoils with leading-edge roughness heights on the order of 140–200 µm while showing poor agreement for smaller roughness heights on the order of 100 µm. Results from the second part of the study indicate that up to a 3.3 % reduction in annual energy production (AEP) can be expected when the LE shape is degraded by 0.8 % of the chord, based on the NREL5MW turbine. The results also suggest that under fully turbulent conditions, the degree of eroded LE shapes studied in this work show the minimal effect on the aerodynamic performances, which results in a negligible difference to AEP.

Experimental Subsonic Flutter of a Linear Turbine Blade Cascade With Various Mode Shapes and Chordwise Torsion Axis Locations

Abstract Axial flow turbomachinery is susceptible to self-excited vibrations known as flutter, primarily affecting high-aspect ratio rotor blades. Experimental studies of blade flutter are essential to understanding the phenomenon. The existing research has shown that the most critical factor in determining the aerodynamic stability of the blade is the mode shape. In this work, measurements of subsonic flutter of a linear turbine blade cascade with various mode shapes and torsion axis locations in a chordwise direction are carried out. The cascade consists of eight blades representing the reduced tip sections of the last stage blade of the steam turbine rotor, and central four flexibly mounted blades are forced to vibrate in pure bending and pure torsion modes and a combined motion. Both the traveling wave mode approach and the influence coefficient method are tested. The results show that the pure torsion mode is insensitive to increasing reduced frequency and is aerodynamically unstable for each positive angle of incidence tested, while pure bending and combined modes become less stable with the increased angle of incidence. In addition, high sensitivity of blade behavior to changes in torsion axis position and phase shift between bending and torsion motions is demonstrated.

The groove at blade tip designed for suppression of tip-leakage vortex may bring the risk of inducing new cavitation

Previous research showed that slotting at the tip section of a rotating machinery blade could suppress the tip-leakage vortex (TLV) by forming a new groove flow, while the possible adverse effects caused by the discontinuous tip section have not fully been studied. In this Letter, unfavorable effects due to an extra cavitation caused by the groove found in the standard incipient cavitation experiments are reported. Then, this anomaly is clarified by using large eddy simulation that the grooves cause step-like flows and induce low-pressure areas behind the groove near the pressure surface. This increased risk of inducing new cavitation deserves special attention when the medium is water.

Theoretical and computational studies on the optimal positions of NACA airfoils used in horizontal axis wind turbine blades

This paper presents a theoretical and computational study to determine the optimal positions of airfoils along the length of the horizontal axis wind turbine blade. We used four and five-digit NACA airfoils to model a 54-meter blade. The lift, drag coefficient, and lift-to-drag ratio of each airfoil are determined by using QBlade software. The aerodynamic performance of the airfoils is studied based on the blade element momentum theory, and Matlab software is used for numerical implementation. The velocity and pressure distributions on each airfoil are assessed using computational fluid dynamics. We implement the thickness distribution techniques to adjust the positions of the airfoils along the length of the blade. It is noted that stresses reach their maximum values at the root and minimum at the tip section. Thus, the thicker (NACA 4420) and thinner (NACA 23012) airfoils are set at 20% of the maximum chord and 91.11% at the tip sections of the blades. The remaining sections of the blade are configured using linear interpolation methods. Specifically, the maximum chord length of the new design is reduced by 18.06% compared to the NACA 23012 rotor blade. Finally, the recommended tip speed ratio for the designed rotor blade is estimated using the graphs of the normal and tangential forces, thereby producing a safe and efficient design.

Aerodynamic Analyses of an Integrated Low-Pressure Compression System for Adaptive-Cycle Micro Turbofan Type Jet Engine

Unmanned Aerial Vehicles (UAVs) are commonly propeller-driven and low-speed. The concept of cost-efficient, much higher speed and longer range applications of micro jet engines was previously addressed such that an existing basic turbojet engine was converted into a single spool turbofan without using additional components of booster and low pressure turbine. Normally, this situation emerges matching problems since two spools are required to adjust the fan speed independently. A simple solution was to use a Continuously Variable Transmission (CVT) gearbox to adjust optimal speed for the fan. As a result, missing of the positive functionality of the booster would lump into the fan root to form a unified low pressure compression system (unified-LPC). Such a unified-LPC demands unique characteristics of having an extreme twist, very high pressure ratio and mass flux at the root section than at the tip section, despite the exact opposite is being enforced due to the wheel speed rise with radius. In light of these challenges, this work aims to investigate detailed aerodynamics of an existing design previously made and reported by the authors. It is shown that, despite the aerodynamic loading contrast throughout the span, the unified-LPC can still have a wide operating range and acceptable off-design aerodynamics. Complementing the previous design-oriented work, this paper aims to provide guidelines for such unified compression systems.

Simulation study on the deflection and expansion of hydraulic fractures in coal-rock complexes

The physical difference and structural weak surface of coal-rock complexes greatly influence the morphology of hydraulic fractures (HFs). This study aims to explore the law of deflection and expansion of HFs in coal-rock complexes under different stress conditions. First, a theoretical model for HF deflection in coal-rock complexes was derived. Besides, a numerical model for HF expansion in coal-rock complexes was established based on the traction–separation criterion, the cohesion embedding method and the finite element method for fracture expansion. With the aid of the established model, the laws of morphology and induced stress field evolutions during HF expansion were studied. The following conclusions were drawn. When the HF is closer to the interface, the effect of physical difference is more notable, and the HF is more likely to expand along the coal seam. As the difference between the maximum horizontal principal stress and the vertical ground stress decreases from 8 MPa to 0 MPa, the coal-rock complexes experience HF expansion in the horizontal direction, secondary fracture generation in the Z-axis direction, and HF deflection to the interface in the -Z-axis direction in turn. During HF expansion, a stress difference of about 19 MPa exists between the fracture tip section and the interface, which is favorable for HF initiation and expansion. The effect of physical difference between coal and rock leads to the formation of an induced stress field, which causes a 3–4 times difference in the displacement values in different areas during HF expansion. The abovementioned main causes of HF deflection can provide reference for the design and application of the hydraulic fracturing technology for complex formations with different lithologies.