Theoretical and Computational Fluid Dynamics最新文献

{"title":"Prediction of leading-edge-vortex initiation using criticality of the boundary layer","authors":"Hariharan Ramanathan,&nbsp;Ashok Gopalarathnam","doi":"10.1007/s00162-023-00648-z","DOIUrl":"10.1007/s00162-023-00648-z","url":null,"abstract":"<p>The initiation of leading-edge-vortex formation in unsteady airfoil flows is governed by flow criticality at the leading edge. While earlier works demonstrated the promise of criticality of leading-edge suction in governing LEV shedding, this criterion is airfoil and Reynolds number dependent. In this work, by examining results from Navier–Stokes computations for a large set of pitching airfoil cases at laminar flow conditions, we show that the onset of flow reversal at the leading edge always corresponds to the boundary-layer shape factor reaching the same critical value that governs laminar flow separation in steady airfoil flows. Further, we show that low-order prediction of this boundary-layer criticality is possible with an integral-boundary-layer calculation performed using potential-flow velocity distributions from an unsteady panel method. The low-order predictions agree well with the high-order computational results with a single empirical offset that is shown to work for multiple airfoils. This work shows that boundary-layer criticality governs LEV initiation, and that a low-order prediction approach is capable of predicting this boundary-layer criticality and LEV initiation.</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"37 3","pages":"397 - 420"},"PeriodicalIF":3.4,"publicationDate":"2023-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4552524","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}

{"title":"Active chaotic mixing of yield stress fluids in an open channel flow","authors":"Yann Moguen,&nbsp;Eliane Younes,&nbsp;Kamal El Omari,&nbsp;Cathy Castelain,&nbsp;Yves Le Guer,&nbsp;Teodor Burghelea","doi":"10.1007/s00162-023-00650-5","DOIUrl":"10.1007/s00162-023-00650-5","url":null,"abstract":"<p>A numerical investigation of active mixing of yield stress fluids using a mixer recently proposed in El Omari et al. (Phys Rev Fluids 6(024):502, 2021. https://doi.org/10.1103/PhysRevFluids.6.024502) and tested experimentally with Newtonian fluids (Younes et al. in Int J Heat Mass Transf 187(122):459, 2022) is presented. As the Bingham number (defined by the ratio of the yield stress to the viscous stress) is increased past a critical value <span>(text {Bn}_{textrm{bulk}}^textrm{crit}approx 5)</span>, a dramatic decrease of both the efficiency of the mixing process and of the homogeneity of the final mixture is observed. Further physical insights into this observation are obtained by a systematic analysis of the space-time dynamics of the flow fields in both Eulerian and Lagrangian frames. The numerical results show that the cascade of the passive scalar fluctuations from the wave numbers associated to the integral scale at which the passive scalar is injected down to the diffusive scale is obstructed by the emergence of a supplemental space scale associated to the characteristic size of the un-yielded material elements. The study is complemented by the discussion of two plausible solutions for alleviating the dramatic loss of mixing efficiency induced by the viscoplastic fluid behavior.</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"37 2","pages":"203 - 239"},"PeriodicalIF":3.4,"publicationDate":"2023-05-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4474822","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}

{"title":"Flow dynamics in a model of a dilated thoracic aorta prior to and following prosthetic replacement","authors":"Pier Giuseppe Ledda,&nbsp;Maria Grazia Badas,&nbsp;Gildo Matta,&nbsp;Giorgio Querzoli","doi":"10.1007/s00162-023-00651-4","DOIUrl":"10.1007/s00162-023-00651-4","url":null,"abstract":"<p>We numerically investigate the flow dynamics in a model of a dilated thoracic aorta, and compare the flow features with the case of a prosthetic replacement in its ascending part. The flow is characterized by an inlet jet which impacts the aortic walls and sweeps toward the aortic arch. Secondary flows generated by the transvalvular jet evolve downstream into a helical flow. The small curvature radius at the end of the aortic arch induces flow separation and vortex shedding in the initial part of the descending aorta, during the systole. The implantation of a prosthesis determines several modifications in the global and local flow patterns. An increase of the pulse wave velocity in the aorta leads to larger pressures inside the vessel, due to the geometrical and rigidity modifications. The sweeping jet is more aligned along the axial direction and propagates faster along the aortic arch. Consequently, a stronger separation of the flow downstream of the aortic arch is observed. By also exploiting manifold analysis, we identify regions characterized by near-wall disordered flows which may present intense accumulation and drop of concentration of biochemicals. These regions are localized downstream of the prosthetic replacement, in the aortic arch, and may be more prone to a new emergence of vessel dilation.</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"37 3","pages":"375 - 396"},"PeriodicalIF":3.4,"publicationDate":"2023-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00162-023-00651-4.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4398732","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}

{"title":"Effects of annulation on low Reynolds number flows over an orthocone","authors":"Mitesh Thakor,&nbsp;Kee Horng Seh,&nbsp;Sareta R. Gladson,&nbsp;Martin L. Fernandez,&nbsp;Linda C. Ivany,&nbsp;Melissa Green,&nbsp;Yiyang Sun","doi":"10.1007/s00162-023-00649-y","DOIUrl":"10.1007/s00162-023-00649-y","url":null,"abstract":"<p>This study numerically examines the influences of transverse annulation around a cone surface on the characteristics of a flow over an orthocone. This work is inspired by <i>Spyroceras</i>, a fossilized genus of nautiloid cephalopods from the Paleozoic era, whose method of locomotion is understudied. As a baseline case, a flow over a smooth orthoconic model with a blunt cone end is investigated numerically at Reynolds numbers from 500 to 1500. As Reynolds increases, two different shedding mechanisms—hairpin-vortex wake and spiral-vortex wake—are captured. We notice that an introduction of annulation over the cone surface changes the critical Reynolds number for the transition of the shedding mechanism. The dominant shedding frequency increases with the Reynolds number for the smooth and annulated cone flows. Moreover, the annulation reduces the dominant frequency for the same Reynolds number and increases the time-averaged drag coefficient. Modal decompositions—Proper Orthogonal Decomposition (POD) and Spectral Proper Orthogonal Decomposition (SPOD)—are used to capture the coherent structures and their oscillating frequencies. We have captured modes corresponding to the hairpin-vortex wake and spiral-vortex wake shedding mechanisms. Comparing the leading POD modes for the smooth and the annulated cone flows, we find that the annulation can reduce the twisting effects of the coherent structures in the wake. Additionally, we find that the SPOD analysis can identify modes presenting both hairpin-vortex wake and spiral-vortex wake in one flow condition as leading modes, while the POD leading modes only reveal one shedding mechanism in each flow.</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"37 3","pages":"357 - 374"},"PeriodicalIF":3.4,"publicationDate":"2023-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00162-023-00649-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4267906","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}

{"title":"Simulation of droplet impact dynamics on V-shaped walls","authors":"Guoqiang Wu,&nbsp;Sheng Chen","doi":"10.1007/s00162-023-00652-3","DOIUrl":"10.1007/s00162-023-00652-3","url":null,"abstract":"<p>This paper presents the morphological evolution characteristics of a droplet impacting a V-shaped wall by using the lattice Boltzmann method (LBM). Four parameters are investigated comprehensively. The parameters vary over wide ranges: surface wettability (<span>(60^circ le theta ^{eq} le 120^circ )</span>), Weber number (<span>(102.27 le text {We} le 3681.82)</span>), bending angle of the V-shaped wall (90<span>(^circ le theta le 180^circ )</span>), and eccentricity ratio (0 <span>(le b le )</span> 0.5). Two types of collision are observed: deposition and breakage. For breakage, the number of satellite droplets increases against the increment of We. The splashing occurs for a high We. And the lamella ejection is observed on the hydrophilic wall and the neutral wall. The lamella ejection will be slight against the increase of <span>(theta ^{eq})</span>, while it will become obvious against the increment of <span>(theta )</span>. In addition, the nondimensional spreading length, width, and height are measured and analyzed. Regime maps are established based on We, Re, and <span>(theta )</span>.</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"37 2","pages":"173 - 202"},"PeriodicalIF":3.4,"publicationDate":"2023-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4224402","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}

{"title":"Vortex dynamics of axisymmetric cones at high angles of attack","authors":"Al Shahriar,&nbsp;Rajan Kumar,&nbsp;Kourosh Shoele","doi":"10.1007/s00162-023-00647-0","DOIUrl":"10.1007/s00162-023-00647-0","url":null,"abstract":"<p>Vortex asymmetry, dynamics, and breakdown in the wake of an axisymmetric cone have been investigated using direct numerical simulation for a wide range of angles of attack. The immersed boundary method is employed with pseudo-body-conformal grids to ensure the accuracy and resolution requirements near the body while being able to account for topology changes near the cone tip. The separated shear layer originated from the surface of the cone swirls into a strong primary vortex. Beneath the primary vortex on the leeward surface of the cone, a well-coherent counter-rotating secondary vorticity is generated. Beyond a particular threshold of swirl, the attached vortex structure breaks and the flow undergoes a chaotic transformation. Depending on the angle of attack, the flow shows different levels of instabilities and the topology of the vortices changes in the wake. In addition to swirl, spiral vortices that revolve around the primary vortex core often merge with the core and play a role in developing the double-helix mode of instability at the onset of the vortex breakdown. At the angle of attack of 60<span>(^circ )</span>, the time-averaged side force becomes asymmetric at the stage where the drag overcomes the lift. At the angle of attack of 75<span>(^circ )</span>, the primary vortex governs the flow asymmetry and the side force. Flow asymmetry is independent of the vortex breakdown. Finally, the contribution of primary vortices to the total forces is quantified using a force partitioning method.</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"37 3","pages":"337 - 356"},"PeriodicalIF":3.4,"publicationDate":"2023-05-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4179124","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}

{"title":"Flow over a hydrofoil subjected to traveling wave-based surface undulation: effect of phase difference between surface waves and wave number","authors":"Sarvesh Shukla,&nbsp;Atul Sharma,&nbsp;Amit Agrawal,&nbsp;Rajneesh Bhardwaj","doi":"10.1007/s00162-023-00646-1","DOIUrl":"10.1007/s00162-023-00646-1","url":null,"abstract":"<p>Flow around a traveling wave-based surface-undulating NACA0012 hydrofoil has been numerically studied. In particular, we determine the effect of the phase speed of the wave, the phase difference between the waves traveling on the top and bottom surfaces, and the wave number on flow dynamics around and behind the hydrofoil and propulsive performance. The flow results in a vortex sheet or a street behind the hydrofoil, where oppositely signed vortices are aligned in either forward or reverse direction. Apart from these, side vortices start forming on either side of the hydrofoil at a higher wave number. The phase difference analysis between the upper and lower surface undulation reveals the configuration better for the hydrofoil’s lateral and longitudinal stability. The hydrofoil can shift from high thrust to high lateral force configuration by changing the phase difference between waves on the top and bottom surfaces. Thrust increases with an increase in the wave number, and a threshold value of phase speed and wave number exists where the drag-to-thrust transition happens. The added mass force-based scaling analysis corroborates with the simulated results.</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"37 3","pages":"319 - 336"},"PeriodicalIF":3.4,"publicationDate":"2023-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00162-023-00646-1.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"5106989","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}

{"title":"Passive control of dynamic stall using a flow-driven micro-cavity actuator","authors":"Miguel R. Visbal,&nbsp;Daniel J. Garmann","doi":"10.1007/s00162-023-00645-2","DOIUrl":"10.1007/s00162-023-00645-2","url":null,"abstract":"<p>A novel passive flow control strategy for the mitigation of transient separation and dynamic stall is demonstrated by means of high-fidelity large-eddy simulations. The control technique is based on a properly-sized micro-cavity cut into a wing’s underside near the leading edge, ahead of stagnation. This cavity remains essentially inactive at low incidence. However, as the wing effective angle of attack increases, the stagnation point displaces past the micro-cavity and the accelerating flow grazing the cavity induces a high-frequency resonance phenomenon or so-called Rossiter modes. The self-generated small-scale disturbances are carried around the leading-edge through the boundary layer to the wing’s upper side where the laminar separation bubble (LSB) amplifies these disturbances. This process delays LSB bursting and dynamic stall when the cavity size is selected such that its naturally occurring Rossiter modes are tuned to the receptivity of the LSB. Control effectiveness is explored for a harmonically pitching NACA 0012 wing section with freestream Mach number <span>(M_infty = 0.2)</span>, chord Reynolds numbers <span>(textrm{Re}_textrm{c} = 5 times 10^5)</span>, and maximum angle of attack of <span>(18^circ )</span>. The flow fields are computed employing a validated overset high-order implicit large-eddy simulation (LES) solver based on sixth-order compact schemes for the spatial derivatives augmented with an eighth-order low-pass filter. Despite its simplicity, the micro-cavity resonance is found to be highly effective in preventing the deep dynamic stall experienced by the baseline airfoil. A significant reduction in the cycle-averaged drag and in the force and moment fluctuations is achieved. In addition, the negative (unstable) net-cycle pitch damping found in the baseline cases is eliminated.</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"37 3","pages":"289 - 303"},"PeriodicalIF":3.4,"publicationDate":"2023-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4998499","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}

{"title":"Non-isothermal thin-film flow of a viscoplastic material over topography: critical Bingham number for a partial slump","authors":"Miguel Moyers-Gonzalez,&nbsp;James N. Hewett,&nbsp;Dale R. Cusack,&nbsp;Ben M. Kennedy,&nbsp;Mathieu Sellier","doi":"10.1007/s00162-023-00642-5","DOIUrl":"10.1007/s00162-023-00642-5","url":null,"abstract":"<p>This paper considers the non-isothermal flow of a viscoplastic fluid on a horizontal or an inclined surface with a flat, a step-up and a step-down topography. A particular application of interest is the spread of a fixed mass—a block—of material under its own weight. The rheology of the fluid is described by the Bingham model which includes the effect of yield stress, i.e. a threshold stress which must be exceeded before flow can occur. Both the plastic viscosity and the yield stress are modelled with temperature-dependent parameters. The flow is described by a reduced model with a thin-film equation for the height of the block and a depth-averaged energy conservation equation for the heat transfer. Results show that for large values of the yield stress, only the outer fraction of the fluid spreads outward, the inner fraction remaining unyielded, hence the block only partially slumps. Conversely, for small values of the yield stress, the entire block of fluid becomes yielded and therefore slumps. We present an analysis which predicts the critical value of the yield stress for which partial slump occurs and how it depends on temperature.</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"37 2","pages":"151 - 172"},"PeriodicalIF":3.4,"publicationDate":"2023-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00162-023-00642-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4692654","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}

{"title":"Direct numerical simulations and flow-pressure acoustic analyses of flapping-uvula-induced flow evolutions within normal and constricted pharynx","authors":"Jinxiang Xi,&nbsp;Junshi Wang,&nbsp;Xiuhua April Si,&nbsp;Haibo Dong","doi":"10.1007/s00162-023-00638-1","DOIUrl":"10.1007/s00162-023-00638-1","url":null,"abstract":"<p>Snoring and obstructive sleep apnea (OSA) are often associated with uvula vibrations and pharynx constrictions. However, successful treatment of snoring or accurate diagnosis of OSA has been proven challenging. This study aimed to identify acoustic indexes that were sensitive to underlying airway structural or kinematic variations. Six physiologically realistic models were developed that consisted of three pharynx constriction levels (M1-3) and two uvula-flapping kinematics (K1-2). Direct numerical simulations (DNS) were performed to resolve spatial and temporal flow dynamics, and an immersed boundary method was used to approximate the uvula vibrations. Time-varying acoustic pressures at six points in the pharynx were analyzed using different algorithms in frequency- or frequency–time domains. Signature flow structures formed near the uvula for different uvula motions and in the pharynx for different pharyngeal constriction levels. The fast Fourier transform showed that the acoustic energy was mainly distributed in four peaks (flapping frequency and three harmonics) with descending magnitudes. Their amplitudes and distribution patterns differed among the six models but were not substantial. The continuous wavelet transforms showed clearly separated acoustic cycles (in both frequency and time) in the uvula-induced flows and revealed a cascading bifurcation pattern in the input–output semblance map. Specifically, the multifractal spectrum was sensitive to uvula flapping kinematics but not pharynx constrictions. By contrast, the input–output cross-correlation and Hilbert phase space showed high sensitivity to pharynx constrictions but low sensitivity to uvula kinematics. The frequency–time analyses of DNS-predicted pressures offered insight into the acoustics signals that were not apparent in original signals and could be used individually or in combination in diagnosis or treatment planning for snoring/OSA patients.</p>","PeriodicalId":795,"journal":{"name":"Theoretical and Computational Fluid Dynamics","volume":"37 2","pages":"131 - 149"},"PeriodicalIF":3.4,"publicationDate":"2023-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00162-023-00638-1.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4875982","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}