Pub Date : 2024-12-06DOI: 10.1016/j.ijheatfluidflow.2024.109685
Sandeep Aryal, Kwangkook Jeong
This study focuses on comparing the heat and water recovery performance of two coolants, R134a refrigerant and water, in a low-temperature evaporator (LT-E) designed for a pilot-scale Organic Rankine Cycle (ORC). The primary objectives were to develop a one-dimensional analytical model capable of predicting simultaneous phase transitions—internal flow boiling of R134a and condensation of water vapor from flue gas on the outer tube wall—and to compare the heat and mass transfer performance of R134a with that of water. Baseline modeling conditions included a flue gas temperature of 57.3 °C, coolant inlet temperature of 16 °C, and a coolant mass velocity of 126.4 kg/sm2, with inlet pressures of 630 kPa for R134a and 100 kPa for water. The model’s predictions showed average discrepancies of 10 % for water recovery efficiency and 3 % for flue gas exit temperature when compared to experimental data. Case studies revealed that R134a outperformed water in heat flux by 16 % to 67 %, and water recovery efficiency was 15 % to 68 % higher with R134a. Increased heat exchanger surface area improved recovery efficiency for both coolants, eventually reaching an asymptotic limit.
{"title":"Analytical modeling of simultaneous phase transitions in a low-temperature evaporator for a pilot-scale Organic Rankine Cycle using R134a: A comparative study with water coolant","authors":"Sandeep Aryal, Kwangkook Jeong","doi":"10.1016/j.ijheatfluidflow.2024.109685","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109685","url":null,"abstract":"<div><div>This study focuses on comparing the heat and water recovery performance of two coolants, R134a refrigerant and water, in a low-temperature evaporator (LT-E) designed for a pilot-scale Organic Rankine Cycle (ORC). The primary objectives were to develop a one-dimensional analytical model capable of predicting simultaneous phase transitions—internal flow boiling of R134a and condensation of water vapor from flue gas on the outer tube wall—and to compare the heat and mass transfer performance of R134a with that of water. Baseline modeling conditions included a flue gas temperature of 57.3 °C, coolant inlet temperature of 16 °C, and a coolant mass velocity of 126.4 kg/sm<sup>2</sup>, with inlet pressures of 630 kPa for R134a and 100 kPa for water. The model’s predictions showed average discrepancies of 10 % for water recovery efficiency and 3 % for flue gas exit temperature when compared to experimental data. Case studies revealed that R134a outperformed water in heat flux by 16 % to 67 %, and water recovery efficiency was 15 % to 68 % higher with R134a. Increased heat exchanger surface area improved recovery efficiency for both coolants, eventually reaching an asymptotic limit.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109685"},"PeriodicalIF":2.6,"publicationDate":"2024-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140135","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-06DOI: 10.1016/j.ijheatfluidflow.2024.109667
Yuki Matsukawa, Takahiro Tsukahara
The Taylor–Couette flow between a stationary outer cylinder and rotating inner cylinder undergoes a supercritical transition. After becoming linearly unstable, the flow becomes progressively more complex: as the inner cylinder rotation Reynolds number increases, the flow state changes to the Taylor vortex flow (TVF) wavy Taylor vortex flow (WVF) modulated wavy Taylor vortex flow (MWV). In contrast, annular Poiseuille flow, driven by an axial pressure gradient in concentric cylinders, undergoes a subcritical transition. Its subcritical turbulent flow features helical-shaped localized turbulence (HLT). The Taylor–Couette–Poiseuille flow, which is a combined shear flow of cylinder-rotation-driven flow and axial pressure-driven flow, is the subject of this study. We investigated the flow state transition processes for a high radius ratio of 0.883 at three different values, using direct numerical simulations. We demonstrated that in the TVF and WVF-based cases, the pressure-driven axial flow stabilized into the Taylor-vortex-free flow field, with the WVF state transitioning to the TVF state before laminarization. A further increase in the axial pressure gradient led to intermittent turbulence, similar to HLT. These facts indicate that the switch from supercritical to subcritical transitions occurs across laminarization. In the MWV-based case, at a higher , the flow does not exhibit laminarization but becomes fully turbulent, unlike in the lower cases. However, the waviness of the Taylor vortex disappeared, and the pre-multiplied energy spectra confirmed partial stabilization before the transition to turbulence. From the perspective of Lumley’s anisotropic invariant map, the TVF- and WVF-based cases have one- or two-component anisotropy under all conditions. However, the MWV-based case becomes continuously similar to the anisotropic map of typical turbulent channel flow as increases.
{"title":"Switching between supercritical and subcritical turbulent transitions in inner cylinder rotating Taylor–Couette–Poiseuille flow","authors":"Yuki Matsukawa, Takahiro Tsukahara","doi":"10.1016/j.ijheatfluidflow.2024.109667","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109667","url":null,"abstract":"<div><div>The Taylor–Couette flow between a stationary outer cylinder and rotating inner cylinder undergoes a supercritical transition. After becoming linearly unstable, the flow becomes progressively more complex: as the inner cylinder rotation Reynolds number <span><math><msub><mrow><mi>Re</mi></mrow><mrow><mi>in</mi></mrow></msub></math></span> increases, the flow state changes to the Taylor vortex flow (TVF) <span><math><mo>→</mo></math></span> wavy Taylor vortex flow (WVF) <span><math><mo>→</mo></math></span> modulated wavy Taylor vortex flow (MWV). In contrast, annular Poiseuille flow, driven by an axial pressure gradient in concentric cylinders, undergoes a subcritical transition. Its subcritical turbulent flow features helical-shaped localized turbulence (HLT). The Taylor–Couette–Poiseuille flow, which is a combined shear flow of cylinder-rotation-driven flow and axial pressure-driven flow, is the subject of this study. We investigated the flow state transition processes for a high radius ratio of 0.883 at three different <span><math><msub><mrow><mi>Re</mi></mrow><mrow><mi>in</mi></mrow></msub></math></span> values, using direct numerical simulations. We demonstrated that in the TVF and WVF-based cases, the pressure-driven axial flow stabilized into the Taylor-vortex-free flow field, with the WVF state transitioning to the TVF state before laminarization. A further increase in the axial pressure gradient led to intermittent turbulence, similar to HLT. These facts indicate that the switch from supercritical to subcritical transitions occurs across laminarization. In the MWV-based case, at a higher <span><math><msub><mrow><mi>Re</mi></mrow><mrow><mi>in</mi></mrow></msub></math></span>, the flow does not exhibit laminarization but becomes fully turbulent, unlike in the lower <span><math><msub><mrow><mi>Re</mi></mrow><mrow><mi>in</mi></mrow></msub></math></span> cases. However, the waviness of the Taylor vortex disappeared, and the pre-multiplied energy spectra confirmed partial stabilization before the transition to turbulence. From the perspective of Lumley’s anisotropic invariant map, the TVF- and WVF-based cases have one- or two-component anisotropy under all conditions. However, the MWV-based case becomes continuously similar to the anisotropic map of typical turbulent channel flow as <span><math><mrow><mi>F</mi><mrow><mo>(</mo><mi>P</mi><mo>)</mo></mrow></mrow></math></span> increases.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109667"},"PeriodicalIF":2.6,"publicationDate":"2024-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140175","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-05DOI: 10.1016/j.ijheatfluidflow.2024.109686
Xinyu Wang , Lin Ye , Cunliang Liu , Xiyuan Liang , Chuxiang Shi
Due to its superior cooling performance, the double-wall structure has become a critical technology for extending the service life of high-temperature components in aeroengines. However, its high flow resistance poses a significant challenge to its application in turbine vanes. This study introduces an innovative double-wall structure incorporating hollow pin-fins to reduce flow resistance and enhance cooling performance. Numerical simulations are conducted to compare this novel structure with traditional double-wall and single-wall configurations. Additionally, the film hole shape of the optimal cooling structure is modified to a laid-back fan shape for further performance improvements. The simulations employ the RANS model, using the SST k-ω turbulence model. Key performance metrics, including the coolant flow coefficient, film cooling effectiveness, target plate Nusselt number, and overall cooling effectiveness, are evaluated for different cooling structures. The results demonstrate a significant reduction in flow resistance for the novel design, as the addition of hollow pin-fins facilitates a coolant outflow mechanism similar to that of a single-wall structure. The novel double-wall design reduces the flow coefficient by 5.4% compared to the single wall. In terms of cooling performance, the hollow pin-fins positioned on the spanwise sides of the film holes help prevent film detachment at high blowing ratios, while the pin–fin in the impingement chamber increases the internal heat transfer surface area. Overall, the cooling effectiveness of the novel design improves by up to 4.6% compared to the traditional double-wall structure. When laid-back fan-shaped holes are applied to the novel double-wall structure, further reductions in flow resistance and enhancements in cooling performance are observed. The increased channel area allows for a 6.7% increase in the flow coefficient compared to the single wall. Moreover, the double-wall structure with laid-back fan-shaped holes significantly enhances film adhesion, leading to a 70.0% improvement in film effectiveness and a 15.9% increase in overall cooling effectiveness compared to traditional double-walls.
{"title":"Investigation of the cooling characteristics of a Low-Resistance Double-Wall configuration with hollow Pin-Fins","authors":"Xinyu Wang , Lin Ye , Cunliang Liu , Xiyuan Liang , Chuxiang Shi","doi":"10.1016/j.ijheatfluidflow.2024.109686","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109686","url":null,"abstract":"<div><div>Due to its superior cooling performance, the double-wall structure has become a critical technology for extending the service life of high-temperature components in aeroengines. However, its high flow resistance poses a significant challenge to its application in turbine vanes. This study introduces an innovative double-wall structure incorporating hollow pin-fins to reduce flow resistance and enhance cooling performance. Numerical simulations are conducted to compare this novel structure with traditional double-wall and single-wall configurations. Additionally, the film hole shape of the optimal cooling structure is modified to a laid-back fan shape for further performance improvements. The simulations employ the RANS model, using the SST <em>k-ω</em> turbulence model. Key performance metrics, including the coolant flow coefficient, film cooling effectiveness, target plate Nusselt number, and overall cooling effectiveness, are evaluated for different cooling structures. The results demonstrate a significant reduction in flow resistance for the novel design, as the addition of hollow pin-fins facilitates a coolant outflow mechanism similar to that of a single-wall structure. The novel double-wall design reduces the flow coefficient by 5.4% compared to the single wall. In terms of cooling performance, the hollow pin-fins positioned on the spanwise sides of the film holes help prevent film detachment at high blowing ratios, while the pin–fin in the impingement chamber increases the internal heat transfer surface area. Overall, the cooling effectiveness of the novel design improves by up to 4.6% compared to the traditional double-wall structure. When laid-back fan-shaped holes are applied to the novel double-wall structure, further reductions in flow resistance and enhancements in cooling performance are observed. The increased channel area allows for a 6.7% increase in the flow coefficient compared to the single wall. Moreover, the double-wall structure with laid-back fan-shaped holes significantly enhances film adhesion, leading to a 70.0% improvement in film effectiveness and a 15.9% increase in overall cooling effectiveness compared to traditional double-walls.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109686"},"PeriodicalIF":2.6,"publicationDate":"2024-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140177","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-03DOI: 10.1016/j.ijheatfluidflow.2024.109684
Y.A. Altaharwah , C.M. Hsu , R.H. Wang
The effect of pulsation intensity on flow and dispersion characteristics of single-pulsed dual parallel plane jets was experimentally investigated in this study. A single jet from a pair of dual jets was pulsed by a loudspeaker. The flow evolution processes were examined using the laser-light sheet-assisted smoke flow visualization method. The visual spread of the jet flow was measured using the binary boundary edge detection technique. A hotwire anemometer was used to detect the instantaneous velocities, mean velocities, turbulence intensities, Lagrangian integral time, and length scales. The dispersion capabilities of the jet fluid were evaluated employing the tracer-gas concentration detection technique. Two characteristic flow modes, namely the coherent vortices and vortex breakup, could be classified based on pulsation intensity. At Ip < 1.0, the flow was characterized by coherent vortices, which maintained coherence within one excitation cycle. At Ip > 1.0, vortex breakup occurred, where vortices deformed, lost coherence, and transformed into puff-shaped vortical structures within one excitation cycle. The vortices emerging from the pulsed jet undergo deformation, evolving into puff-shaped vortices, and subsequently fragment into smaller turbulent eddies more quickly than the synchronized vortices from the non-pulsed jet. This leads to significant penetration and velocity fluctuations in the trajectory of the pulsed jet. Consequently, the overall spread width and concentration reduction index of the single-pulsed dual parallel plane jets exceed those of the non-pulsed dual parallel plane jets.
{"title":"Effect of pulsation intensity on flow and dispersion characteristics of single-pulsed dual parallel plane jets","authors":"Y.A. Altaharwah , C.M. Hsu , R.H. Wang","doi":"10.1016/j.ijheatfluidflow.2024.109684","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109684","url":null,"abstract":"<div><div>The effect of pulsation intensity on flow and dispersion characteristics of single-pulsed dual parallel plane jets was experimentally investigated in this study. A single jet from a pair of dual jets was pulsed by a loudspeaker. The flow evolution processes were examined using the laser-light sheet-assisted smoke flow visualization method. The visual spread of the jet flow was measured using the binary boundary edge detection technique. A hotwire anemometer was used to detect the instantaneous velocities, mean velocities, turbulence intensities, Lagrangian integral time, and length scales. The dispersion capabilities of the jet fluid were evaluated employing the tracer-gas concentration detection technique. Two characteristic flow modes, namely the <em>coherent vortices</em> and <em>vortex breakup</em>, could be classified based on pulsation intensity. At <em>I</em><sub>p</sub> < 1.0, the flow was characterized by coherent vortices, which maintained coherence within one excitation cycle. At <em>I</em><sub>p</sub> > 1.0, vortex breakup occurred, where vortices deformed, lost coherence, and transformed into puff-shaped vortical structures within one excitation cycle. The vortices emerging from the pulsed jet undergo deformation, evolving into puff-shaped vortices, and subsequently fragment into smaller turbulent eddies more quickly than the synchronized vortices from the non-pulsed jet. This leads to significant penetration and velocity fluctuations in the trajectory of the pulsed jet. Consequently, the overall spread width and concentration reduction index of the single-pulsed dual parallel plane jets exceed those of the non-pulsed dual parallel plane jets.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109684"},"PeriodicalIF":2.6,"publicationDate":"2024-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140138","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-03DOI: 10.1016/j.ijheatfluidflow.2024.109675
Junwoo Jae , Hyung Jin Sung , Jinyul Hwang
Reducing the skin-friction drag in wall turbulence is crucial for minimizing energy consumption in various industrial applications. Although numerous studies have proposed strategies for skin-friction reduction, their effectiveness generally degrades at high Reynolds numbers (Re) owing to the multiscale nature of wall turbulence. To address this challenge, it is necessary to understand coherent structures that span a wider range at high Re, particularly those that extend down to the wall. Hence, we explore wall-attached momentum transfer structures in drag-reduced flows and investigate the associated Re effects on the skin-friction reduction. We perform direct numerical simulations of drag-reduced flows at two bulk Re of 10,000 and 20,000 by employing the Navier slip boundary condition. For comparison, we conduct no-slip cases at the same bulk Re. We extract clusters of intense ejections and sweeps responsible for momentum transfer in instantaneous flow fields. We observe that wall-attached momentum transfer structures play a dominant role in the turbulent skin friction quantified through the FIK identity (Fukagata et al., 2002). These structures are classified into buffer-layer, self-similar, and non-self-similar ones according to their height. The self-similar structures not only exhibit geometrical self-similarity but also maintain their Reynolds shear stress distribution relative to the local Reynolds shear stress under slip conditions. Moreover, these self-similar structures show nearly identical skin-friction reduction across all heights. In contrast, the non-self-similar structures exhibit a significant difference under slip conditions, especially at a high Re. The reduced area fraction and volume of non-self-similar structures, along with decreased wall-normal transport under slip conditions, result in a greater skin-friction reduction compared to that observed at the low Re. Our findings advance the understanding of the scale-dependent behavior of wall-attached structures in drag-reduced flows, paving the way for the development of new drag-reduction methods through the strategic manipulation of these structures.
{"title":"Contribution of wall-attached momentum transfer structures to the skin friction in slip channel flows","authors":"Junwoo Jae , Hyung Jin Sung , Jinyul Hwang","doi":"10.1016/j.ijheatfluidflow.2024.109675","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109675","url":null,"abstract":"<div><div>Reducing the skin-friction drag in wall turbulence is crucial for minimizing energy consumption in various industrial applications. Although numerous studies have proposed strategies for skin-friction reduction, their effectiveness generally degrades at high Reynolds numbers (Re) owing to the multiscale nature of wall turbulence. To address this challenge, it is necessary to understand coherent structures that span a wider range at high Re, particularly those that extend down to the wall. Hence, we explore wall-attached momentum transfer structures in drag-reduced flows and investigate the associated Re effects on the skin-friction reduction. We perform direct numerical simulations of drag-reduced flows at two bulk Re of 10,000 and 20,000 by employing the Navier slip boundary condition. For comparison, we conduct no-slip cases at the same bulk Re. We extract clusters of intense ejections and sweeps responsible for momentum transfer in instantaneous flow fields. We observe that wall-attached momentum transfer structures play a dominant role in the turbulent skin friction quantified through the FIK identity (<span><span>Fukagata et al., 2002</span></span>). These structures are classified into buffer-layer, self-similar, and non-self-similar ones according to their height. The self-similar structures not only exhibit geometrical self-similarity but also maintain their Reynolds shear stress distribution relative to the local Reynolds shear stress under slip conditions. Moreover, these self-similar structures show nearly identical skin-friction reduction across all heights. In contrast, the non-self-similar structures exhibit a significant difference under slip conditions, especially at a high Re. The reduced area fraction and volume of non-self-similar structures, along with decreased wall-normal transport under slip conditions, result in a greater skin-friction reduction compared to that observed at the low Re. Our findings advance the understanding of the scale-dependent behavior of wall-attached structures in drag-reduced flows, paving the way for the development of new drag-reduction methods through the strategic manipulation of these structures.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109675"},"PeriodicalIF":2.6,"publicationDate":"2024-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140176","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-02DOI: 10.1016/j.ijheatfluidflow.2024.109655
T. Jardin, V. Ferrand, E.R. Gowree
The transitional flow past a NACA0012 airfoil at Reynolds numbers, , between 50,000 and 140,000 is investigated using experiments and low and high-fidelity numerical simulations. Variations in Reynolds number provide the quasi-steady response of the flow and resulting lift to dynamic inflow (varying freestream velocity) conditions addressed in a following paper. It is shown that non-linearity of the quasi-steady response in lift to changes in freestream velocity is highly dependent on angle of attack and is typically promoted when the flow transitions from laminar separation without reattachment to laminar separation with reattachment as the Reynolds number increases. The correlation between flow topology and lift is highlighted using the force partitioning method, which provides a new interpretation for the existence of a shift from negative to positive lift and slope breaks in the lift versus angle of attack (and Reynolds number) curve.
{"title":"NACA0012 airfoil at Reynolds numbers between 50,000 and 140,000 — Part 1: Steady freestream","authors":"T. Jardin, V. Ferrand, E.R. Gowree","doi":"10.1016/j.ijheatfluidflow.2024.109655","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109655","url":null,"abstract":"<div><div>The transitional flow past a NACA0012 airfoil at Reynolds numbers, <span><math><mrow><mi>R</mi><mi>e</mi></mrow></math></span>, between 50,000 and 140,000 is investigated using experiments and low and high-fidelity numerical simulations. Variations in Reynolds number provide the quasi-steady response of the flow and resulting lift to dynamic inflow (varying freestream velocity) conditions addressed in a following paper. It is shown that non-linearity of the quasi-steady response in lift to changes in freestream velocity is highly dependent on angle of attack and is typically promoted when the flow transitions from laminar separation without reattachment to laminar separation with reattachment as the Reynolds number increases. The correlation between flow topology and lift is highlighted using the force partitioning method, which provides a new interpretation for the existence of a shift from negative to positive lift and slope breaks in the lift versus angle of attack (and Reynolds number) curve.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"112 ","pages":"Article 109655"},"PeriodicalIF":2.6,"publicationDate":"2024-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143140139","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-01DOI: 10.1016/j.ijheatfluidflow.2024.109565
Jiabin Wang , Haoyuan Liu , Tianyun Dong , Kan He , Jie Zhang , Guangjun Gao , Branislav Basara , Sinisa Krajnović
The paper presents a numerical investigation into the aerodynamic behaviors of a representative high-speed train model. A thorough comparison of external flow is carried out, involving Partially Averaged Navier-Stokes (PANS), Large Eddy Simulation (LES), and wind tunnel experiments. The train model is scaled down to 1/20 of its actual size. The Reynolds number for both simulations and experiments is fixed at Re = 2.45 × 105, calculated using the inlet velocity Uinf = 20 m/s and the height of the train model H=0.18 m. Three different grid resolutions are utilized in the LES and PANS simulations. A comparison is made between time-averaged and instantaneous flow patterns, velocity, and Reynolds stress profiles under conditions both with and without a yaw angle. The findings indicate that PANS effectively captures the primary flow characteristics of the train’s external flow, with medium PANS closely aligning with fine LES and experimental measurements. Moreover, PANS surpasses LES at lower grid resolutions, showcasing the potential of PANS in effectively resolving the multi-scale instantaneous flow around the train model with relatively modest computational resources.
{"title":"Validation of partially averaged Navier-Stokes and prediction for the turbulent flow past a generic high-speed train with and without yaw angle","authors":"Jiabin Wang , Haoyuan Liu , Tianyun Dong , Kan He , Jie Zhang , Guangjun Gao , Branislav Basara , Sinisa Krajnović","doi":"10.1016/j.ijheatfluidflow.2024.109565","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109565","url":null,"abstract":"<div><div>The paper presents a numerical investigation into the aerodynamic behaviors of a representative high-speed train model. A thorough comparison of external flow is carried out, involving Partially Averaged Navier-Stokes (PANS), Large Eddy Simulation (LES), and wind tunnel experiments. The train model is scaled down to 1/20 of its actual size. The Reynolds number for both simulations and experiments is fixed at <em>R</em>e = 2.45 × 10<sup>5</sup>, calculated using the inlet velocity <em>U<sub>inf</sub></em> = 20 m/s and the height of the train model <em>H</em>=0.18 m. Three different grid resolutions are utilized in the LES and PANS simulations. A comparison is made between time-averaged and instantaneous flow patterns, velocity, and Reynolds stress profiles under conditions both with and without a yaw angle. The findings indicate that PANS effectively captures the primary flow characteristics of the train’s external flow, with medium PANS closely aligning with fine LES and experimental measurements. Moreover, PANS surpasses LES at lower grid resolutions, showcasing the potential of PANS in effectively resolving the multi-scale instantaneous flow around the train model with relatively modest computational resources.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109565"},"PeriodicalIF":2.6,"publicationDate":"2024-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143170949","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-01DOI: 10.1016/j.ijheatfluidflow.2024.109661
E. Salcedo , J.C. Cajas , C. Treviño , L. Martínez-Suástegui
The linear stability and the nonlinear behavior of a two-dimensional magnetohydrodynamic (MHD) opposing mixed convection flow of an electrically conducting fluid mixture in a partially and symmetrically heated vertical channel of finite length under an applied transverse magnetic field is studied using numerically generated perturbed functions. The problem depends on the following dimensionless parameters of the fluid mixture: the flow Reynolds number (), the Prandtl number (), the Richardson number (), and the Hartmann () number, together with geometrical parameters of the vertical channel. The nonlinear behavior is studied by solving numerically the full nonlinear equations and employing a temporal asymmetric perturbation of the number. The nonlinear stability results show that for relatively large values of the number, the flow is stable and the evolution of the heat transfer response is symmetric. For decreasing values of the number, for a critical value of , symmetry breaks and a stable nonsymmetric flow and heat transfer response is reached. Our findings reveal the existence of a hysteresis loop describing the nonlinear behavior for the resulting evolution of the overall Nusselt numbers at different numbers. A linear stability analysis using a symmetrical non-parallel thermal base flow has also been performed for the same parameter values. The symmetric flow system shows instability for a critical value of , where the vertical separation of the two vortical structures oscillates with a fixed dimensionless frequency of . The results show that the nonlinear behavior using the full nonlinear equations reveals hidden instability for the linear analysis. Furthermore, we demonstrate that for the chosen set of parameters and at sufficient high values of the number, the complex interactions related to the effects of shear, opposing buoyancy, and magnetic damping can be effectively used to stabilize the flow.
{"title":"Magnetohydrodynamic instability in a partially heated vertical channel","authors":"E. Salcedo , J.C. Cajas , C. Treviño , L. Martínez-Suástegui","doi":"10.1016/j.ijheatfluidflow.2024.109661","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109661","url":null,"abstract":"<div><div>The linear stability and the nonlinear behavior of a two-dimensional magnetohydrodynamic (MHD) opposing mixed convection flow of an electrically conducting fluid mixture in a partially and symmetrically heated vertical channel of finite length under an applied transverse magnetic field is studied using numerically generated perturbed functions. The problem depends on the following dimensionless parameters of the fluid mixture: the flow Reynolds number (<span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mn>100</mn></mrow></math></span>), the Prandtl number (<span><math><mrow><mi>P</mi><mi>r</mi><mo>=</mo><mn>7</mn></mrow></math></span>), the Richardson number (<span><math><mrow><mi>R</mi><mi>i</mi><mo>=</mo><mn>7</mn></mrow></math></span>), and the Hartmann (<span><math><mrow><mi>H</mi><mi>a</mi></mrow></math></span>) number, together with geometrical parameters of the vertical channel. The nonlinear behavior is studied by solving numerically the full nonlinear equations and employing a temporal asymmetric perturbation of the <span><math><mrow><mi>H</mi><mi>a</mi></mrow></math></span> number. The nonlinear stability results show that for relatively large values of the <span><math><mrow><mi>H</mi><mi>a</mi></mrow></math></span> number, the flow is stable and the evolution of the heat transfer response is symmetric. For decreasing values of the <span><math><mrow><mi>H</mi><mi>a</mi></mrow></math></span> number, for a critical value of <span><math><mrow><mi>H</mi><mi>a</mi><mo>=</mo><mn>4</mn></mrow></math></span>, symmetry breaks and a stable nonsymmetric flow and heat transfer response is reached. Our findings reveal the existence of a hysteresis loop describing the nonlinear behavior for the resulting evolution of the overall Nusselt numbers at different <span><math><mrow><mi>H</mi><mi>a</mi></mrow></math></span> numbers. A linear stability analysis using a symmetrical non-parallel thermal base flow has also been performed for the same parameter values. The symmetric flow system shows instability for a critical value of <span><math><mrow><mi>H</mi><mi>a</mi><mo>=</mo><mn>3</mn><mo>.</mo><mn>68</mn></mrow></math></span>, where the vertical separation of the two vortical structures oscillates with a fixed dimensionless frequency of <span><math><mrow><mi>S</mi><mi>t</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>011</mn></mrow></math></span>. The results show that the nonlinear behavior using the full nonlinear equations reveals hidden instability for the linear analysis. Furthermore, we demonstrate that for the chosen set of parameters and at sufficient high values of the <span><math><mrow><mi>H</mi><mi>a</mi></mrow></math></span> number, the complex interactions related to the effects of shear, opposing buoyancy, and magnetic damping can be effectively used to stabilize the flow.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109661"},"PeriodicalIF":2.6,"publicationDate":"2024-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143104350","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-01DOI: 10.1016/j.ijheatfluidflow.2024.109653
Shao-Wen Chen , Pei-Syuan Ruan , Lung-Hung Huang , Wen-Chen Tsai , Hsiang Lee , Chia-Kuan Chen , Min-Song Lin , Jong-Rong Wang , Jin-Der Lee
Air-water two-phase flow tests were performed in a 3X3 rod bundle channel under low gas-flow conditions. Gas and liquid superficial velocities of < jg> = 0.035–1.0 m/s and < jf> = 0.6–1.7 m/s were tested, which may cover the flow regimes of bubbly to cap-bubbly or slug/churn flows, and global and local void fractions were measured via non-intrusive conductivity void meters at different axial locations. The transient void signals were analyzed with cross-correlation technique to obtain the void structure velocities at various local/global regions, and these velocities were compared with one-dimensional (1D) drift-flux model. Under relatively low gas flow conditions, the void structure velocities were clearly lower than the average gas velocity estimated by 1D drift-flux model. While increasing gas flow rate, the void structure velocities at different regions can jump up and become comparable to the average gas velocities calculated by the 1D drift-flux model (DFM). These velocity jump conditions could be roughly explained by the changes of bubble sizes/shapes and distributions, and the transition boundaries of velocity jumps can be successfully estimated by introducing energy balance between fluid turbulent kinetic energy and bubble surface free energy of various sizes.
{"title":"Experimental Investigation on void structure velocity and estimation of velocity jump boundaries in a 3X3 rod bundle at low gas flow conditions","authors":"Shao-Wen Chen , Pei-Syuan Ruan , Lung-Hung Huang , Wen-Chen Tsai , Hsiang Lee , Chia-Kuan Chen , Min-Song Lin , Jong-Rong Wang , Jin-Der Lee","doi":"10.1016/j.ijheatfluidflow.2024.109653","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109653","url":null,"abstract":"<div><div>Air-water two-phase flow tests were performed in a 3X3 rod bundle channel under low gas-flow conditions. Gas and liquid superficial velocities of < <em>j</em><sub>g</sub>> = 0.035–1.0 m/s and < <em>j</em><sub>f</sub>> = 0.6–1.7 m/s were tested, which may cover the flow regimes of bubbly to cap-bubbly or slug/churn flows, and global and local void fractions were measured via non-intrusive conductivity void meters at different axial locations. The transient void signals were analyzed with cross-correlation technique to obtain the void structure velocities at various local/global regions, and these velocities were compared with one-dimensional (1D) drift-flux model. Under relatively low gas flow conditions, the void structure velocities were clearly lower than the average gas velocity estimated by 1D drift-flux model. While increasing gas flow rate, the void structure velocities at different regions can jump up and become comparable to the average gas velocities calculated by the 1D drift-flux model (DFM). These velocity jump conditions could be roughly explained by the changes of bubble sizes/shapes and distributions, and the transition boundaries of velocity jumps can be successfully estimated by introducing energy balance between fluid turbulent kinetic energy and bubble surface free energy of various sizes.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"110 ","pages":"Article 109653"},"PeriodicalIF":2.6,"publicationDate":"2024-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143171735","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-29DOI: 10.1016/j.ijheatfluidflow.2024.109673
Jia-ao Dai , Yong fa Diao , Lei Zhang
Achieving rapid fabric drying and ensuring a uniform distribution of surface temperature and moisture is essential for the post-processing stage in printing and dyeing. Although jet technology is commonly used to enhance heat transfer processes, the mechanism of heat and moisture transfer using array opposed jet for fabric drying is still unclear. This paper proposes that using opposed jet to enhance the drying process for four different fabric structural types, the influence of jet Reynolds number and excess temperature on the change of fabric moisture content was analyzed using experimental methods, then by defining the fabric as a porous medium containing two-phase components, the flow characteristics and temperature field distribution of the opposed jet were obtained using numerical methods. The results indicated that the four different structural types of fabrics exhibited similar heat-moisture transfer characteristics under the air supply mode of the opposed jet. Furthermore, the critical evaporation temperature of fabrics with hygroscopic properties was higher than that of non-hygroscopic fabrics. When the Reynolds number increased from 649.4 to 2165.3 and the excess temperature increased from 40 ℃ to 70 ℃, the drying time was shortened by a maximum of 56.2 % and 25.5 %, respectively. Under the impact of the array opposed jet, the thermal boundary layer on the fabric surface was thinned, and the local Nusselt number presented different peaks along the length direction of the impinging surface. Within the range of operating conditions considered, at a jet wind speed of 4.5 m/s and an excess temperature of 70 ℃, the maximum surface drying rate of the fabric was achieved. The relative deviations of heat flux and mass flux on the impact surface are all within 10 %. This study provides a theoretical basis for the structural design and drying mechanism exploration of fabric drying equipment.
{"title":"Enhancing heat and moisture transfer of porous fabrics using arrayed opposed jets: Experimental and numerical investigations","authors":"Jia-ao Dai , Yong fa Diao , Lei Zhang","doi":"10.1016/j.ijheatfluidflow.2024.109673","DOIUrl":"10.1016/j.ijheatfluidflow.2024.109673","url":null,"abstract":"<div><div>Achieving rapid fabric drying and ensuring a uniform distribution of surface temperature and moisture is essential for the post-processing stage in printing and dyeing. Although jet technology is commonly used to enhance heat transfer processes, the mechanism of heat and moisture transfer using array opposed jet for fabric drying is still unclear. This paper proposes that using opposed jet to enhance the drying process for four different fabric structural types, the influence of jet Reynolds number and excess temperature on the change of fabric moisture content was analyzed using experimental methods, then by defining the fabric as a porous medium containing two-phase components, the flow characteristics and temperature field distribution of the opposed jet were obtained using numerical methods. The results indicated that the four different structural types of fabrics exhibited similar heat-moisture transfer characteristics under the air supply mode of the opposed jet. Furthermore, the critical evaporation temperature of fabrics with hygroscopic properties was higher than that of non-hygroscopic fabrics. When the Reynolds number increased from 649.4 to 2165.3 and the excess temperature increased from 40 ℃ to 70 ℃, the drying time was shortened by a maximum of 56.2 % and 25.5 %, respectively. Under the impact of the array opposed jet, the thermal boundary layer on the fabric surface was thinned, and the local Nusselt number presented different peaks along the length direction of the impinging surface. Within the range of operating conditions considered, at a jet wind speed of 4.5 m/s and an excess temperature of 70 ℃, the maximum surface drying rate of the fabric was achieved. The relative deviations of heat flux and mass flux on the impact surface are all within 10 %. This study provides a theoretical basis for the structural design and drying mechanism exploration of fabric drying equipment.</div></div>","PeriodicalId":335,"journal":{"name":"International Journal of Heat and Fluid Flow","volume":"111 ","pages":"Article 109673"},"PeriodicalIF":2.6,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142748581","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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