No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
New transition/turbulence model for the flow transition in supersonic boundary layer
Abstract
A new κ-ω-γ transition/turbulence model is established to consider the instability modes associated with the compressibility. The particular features of the new model are: (1) the fluctuating kinetic energy κ includes the non-turbulent, as well as turbulent components modelled with the stability analysis; (2) a function for the source term in γ equation is developed to trigger the transition onset; (3) it is strictly based on local variables by introducing a new length scale normal to wall and compatible with the modern CFD methods. The present model was numerically proved to be applied into the analyses of natural transition and bypass transition with a wide range of Mach number.
... The so-called correlationbased models232425 have become helpful tools for industry owing to their use of integral (or global) boundary layer parameters. Recently, transport equation models26272829 which rely on (local ) information to circumvent some complicated procedures in the early methods, have been introduced. These transport equation models solve several ''transport'' partial differential equations written for various transition quantities in addition to the baseline turbulence models. ...
... Some of these models are the intermittency transport equation models of Suzen and Huang [24,25] and the correlation-based k–ω SST transition model of Menter et al. [26] . More recently truly single point RANS approaches such as the k–k L –ω transition model of Walters and Leylek [28] which essentially eliminate the need for the intermittency , and a variant of the SST model called the k–ω–γ model of Fu and Wang [29] have been introduced. Such models are suitable for straightforward implementation within RANS methods as they solve additional transport equations for predicting transition phenomena that rely on local information only, in contrast with the global information, as used in the early methods. ...
... Transition correlations are user dependent data retrieved from benchmark experiments obtained at different laboratories. A number of investigators have tried to develop their own correlations of the model parameters against different experimental cases [29,30] as the original parameter set remains proprietary [26]. The k–k L –ω model [28] is considered as a three-equation eddyviscosity type, which includes transport equations for turbulent kinetic energy (k), laminar kinetic energy (k L ), and specific dissipation rate (ω). ...
Transition-sensitive, single point eddy viscosity models are fairly new and performance assessment of these models is required. In this study, the performance of transition and turbulence models is first evaluated for predicting low Re number flows having laminar separation bubbles that are traditionally quite difficult to predict for RANS-based CFD methods. Second, suppression of the laminar separation bubbles using blowing and/or suction is investigated for a single aerofoil. A prior experimental study using hot-wire anemometry for a clean (no jet) NACA 2415 aerofoil at α=8° at a Reynolds number of 2×105 shows the presence of a laminar separation bubble. For this flow, the recently developed k–kL–ω transition model is first shown to accurately predict the location and extent of the experimentally measured separation bubble. Following this, the same transition model was used to predict the flow over the NACA 2415 aerofoil using single or simultaneous blowing or suction. In the single blowing or suction cases, the separation bubble is not completely eliminated, but either abated or moved downstream. Smaller blowing velocity ratios cause more effective suppression of the separation bubble than larger blowing ratios, independent of the blowing locations. In contrast, larger suction velocity ratios are better than smaller suction ratios for the suppression. Moreover, the lift/drag ratios increase as the jet location moves from the leading edge to a downstream direction in both cases. In the simultaneous blowing and suction cases, the k–kL–ω transition model is shown to suppress the separation bubble by using a mix of jet parameters which result in increased lift/drag ratios.
... Walters & Leylek [29] adopted Mayle & Schulz's [28] idea and developed a locally formulated transport equation for the laminar kinetic energy that describes the development of the non-turbulent streamwise fluctuations in the pre-transitional boundary layer region, but Walters & Leylek' transition model has too many model constants. In order to model of the high-speed flow transition, Wang & Fu [30] developed a k−ω −γ three-equation approach that is capable of accommodating the effect of the second instability mode, while non-local parameter is required in Wang & Fu's transition model such as the local mean velocity at the generalized inflection point. ...
... Fig. 12 represents the computation results of non-turbulent viscosity, we can observe that the non-turbulent viscosity is near zero in the laminar region and fully turbulent region as the streaky fluctuations will break down and will not exist in the fully turbulent region, so we can deduce that the transport equation of nonturbulent viscosity can predict the correct distribution and is responsible for the bypass transition process. Due to the dissipation term of the non-turbulent viscosity transport equation, the value of the non-turbulent viscosity will be zero in the post-transitional region what is physical and different to Warren & Hassan [29] and Fu & Wang [30] models. But we can also observe that the non-turbulent viscosity does not decay quickly outside the boundary layer in the fully turbulent region in Fig. 12, and the dissipation term of the non-turbulent viscosity transport equation should be improved in the future. ...
It is very important to predict the bypass transition in the simulation of flows through turbomachinery. This paper presents a four-equation eddy-viscosity turbulence transition model for prediction of bypass transition. It is based on the SST turbulencemodel and the laminar kinetic energy concept. A transport equation for the non-turbulent viscosity is proposed to predict the development of the laminar kinetic energy in the pre-transitional boundary layer flow which has been observed in experiments. The turbulence breakdown process is then captured with an intermittency transport equation in the transitional region. The performance of this new transition model is validated through the experimental cases of T3AM, T3A and T3B. Results in this paper show that the new transition model can reach good agreement in predicting bypass transition, and is compatible with modern CFD software by using local variables.
... Researchers in China have also carried out related studies and obtained several promising achievements. In 2009, a new k-ω-γ model was introduced by Wang and Fu [9] , succeeding in predicting boundary transitions in subsonic, supersonic, and hypersonic fields. In the present work, an R t -γ transition prediction model [10] is adopted, which is a brand new model embedding transport equations of intermittency factor with the one-equation R t model [11] . ...
A new transition prediction model is introduced, which couples the intermittency effect into the turbulence transport equations
and takes the characteristics of fluid transition into consideration to mimic the exact process of transition. Test cases
include a two-dimensional incompressible plate and a two-dimensional NACA0012 airfoil. Performance of this transition model
for incompressible flows is studied, with numerical results consistent to experimental data. The requirement of grid resolution
for this transition model is also studied.
... The current chapter is largely based on Langtry and Menter [25]. More recent articles on model validation and development can be found in262728. ...
In this article, autonomous flight performance of an unmanned aerial robot is advanced by benefiting
aerodynamic nose and tail cone shapes redesign both experimentally and computationally. For this
intention, aerodynamic performance criteria (i.e. maximum fineness) of a scaled model of autonomous
aerial robot called as Zanka-II manufactured at Erciyes University Faculty of Aeronautics and
Astronautics Model Aircraft Laboratory is first observed in subsonic Wind Tunnel. Results obtained in
such wind tunnel are subsequently validated using computational fluid dynamic (CFD) software (i.e.
Ansys). Therefore, nose and tail cone of fuselage are improved in order to improve maximum fineness
of the autonomous aerial robot. Finally, a novel scaled model using optimum data is redesigned and
placed in Wind Tunnel to validate Ansys results with experimental results. By using geometrical data of
ultimate aerodynamically optimized aerial robot, better autonomous flight performance is achieved in
both simulation environment (i.e. Matlab and Simulink) and real time flights.
To explore the techniques for mandibular reconstruction with composite free flaps and their outcomes, we systematically reviewed reports published between 1990 and 2015. A total of 9499 mandibular defects were reconstructed with 6178 fibular, 1380 iliac crest, 1127 composite radial, 709 scapular, 63 serratus anterior and rib, 32 metatarsal, and 10 lateral arm flaps including humerus. The failure rate was higher for the iliac crest (6.2%, 66/1059) than for fibular, radial, and scapular flaps combined (3.4%, 202/6018) (p < 0.001).
As a basic problem in many engineering applications, transition from laminar to turbulence still remains a difficult problem in computational fluid dynamics (CFD). A numerical study of one transitional flow in two-dimensional is conducted by Reynolds averaged numerical simulation (RANS) in this paper. Turbulence model plays a significant role in the complex flows’ simulation, and four advanced turbulence models are evaluated. Numerical solution of frictional resistance coefficient is compared with the measured one in the transitional zone, which indicates that Wilcox (2006) k-ω model with correction is the best candidate. Comparisons of numerical and analytical solutions for dimensionless velocity show that averaged streamwise dimensionless velocity profiles correct the shape rapidly in transitional region. Furthermore, turbulence quantities such as turbulence kinetic energy, eddy viscosity, and Reynolds stress are also studied, which are helpful to learn the transition’s behavior.
Introduction:
Mandibular osteoradionecrosis (mORN) is one of the major complications of radiation therapy in head and neck cancer. It is responsible for intractable pain and functional problems. Radical treatment, required in case of failure of conservative management, consists in wide resection of the necrotic tissue followed by reconstruction, notably by free flaps. The present study assessed the efficacy of reconstructive surgery by fibula free flap (FFF) in terms of pain, suppuration and functional results.
Material and methods:
A retrospective study recruited 5 cases of mORN treated surgically with FFF reconstruction between 2005 and 2012. For each patient, pain, resolution of suppuration, articulation, mastication and swallowing functions and recovery of oral feeding were assessed.
Results:
The flaps had good vitality in 4 of the 5 patients. Infection and pain resolved in all patients. Functional results were satisfactory in 4 of the 5 cases (80%). There was no recurrence of mORN.
Conclusions:
Micro-anastomosed FFF seems to be the method of choice for mandibular reconstruction in advanced mORN. Delayed treatment, however, seems to reduce the chances of good functional results. The precise indications for radical surgery and its timing remain to be defined, but it appears wise to decide on ever earlier radical surgery in the hope of obtaining better functional results.
There is a lack of longitudinal data on the effect of osteoradionecrosis (ORN) on health-related quality of life (HRQoL). We report data on HRQoL across groups of patients with ORN at different stages of disease and reconstruction. We identified 71 patients treated for ORN of the mandible, and cross-referenced the data with their medical records. They were divided into 4 groups according to the Notani classification and patients who did not have ORN were used for comparison. Patients with ORN reported the most pain, and rates were relatively high for problems concerning appearance, activity, recreation, swallowing, and chewing. There were significant differences for pain, appearance, swallowing, and chewing between patients who had ORN and those who did not and had not had radiotherapy. On the University of Washington quality of life questionnaire (UWQoL), patients with ORN reported similar levels of morbidity to those who had had radiotherapy but did not have ORN, particularly on the physical and social-emotional subscales. Those with grade III ORN were particularly affected, and the UWQoL scores after mandibular resection and reconstruction were disappointing. HRQoL after composite resection for Notani grade III disease is relatively poor. In patients whose symptoms can be managed without an operation, it seems appropriate to defer resection and reconstruction until there is an appreciable drop in the quality of life, and pain is difficult to control.
Copyright © 2015 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Objective:
Arch bars as treatment for a fractured mandibular condyle are inconvenient to patients and lead to lowered quality of life (QOL). To overcome these inconveniences, IMF-screws (IMFS) to facilitate intermaxillary fixation during surgery have been developed. The purpose of the present study is to investigate and compare QOL for patients treated for a fractured mandibular condyle with either IMFS or arch bars.
Material and methods:
This research trial was conducted from 2010 to 2014 as part of an earlier prospective, multicenter, randomized clinical trial in which the use of IMFS was compared to the use of arch bars in the treatment of mandibular condylar fractures.
Results:
In total, 50 patients were included: 30 (60%) male patients and 20 (40%) female patients (mean age: 31.8 years, standard deviation [SD] = 13.9 years, range = 18-64 years). A total of 24 (48%) patients were allocated in the IMFS group, and 26 (52%) patients were assigned to the arch-bars control group. Significant results were observed in the subscales social isolation, possibility to eat and vary diet, influence on sleep, and satisfaction with the given treatment, all in favour of IMFS.
Conclusion:
In conclusion, using IMFS as a method for conservative treatment of condylar fractures led to a higher QOL during the 6-week period of fracture healing. In comparison to arch bars, patients treated with IMFS experienced less social isolation, had fewer problems with eating, and express the feeling they are able to continue their normal diet. Furthermore it seems that the use of IMFS has a lower negative impact on social and financial aspects of the patient.
Control of flow over a NACA2415 aerofoil which experiences a laminar separation bubble for a transitional Reynolds number of 2×10 5 is numerically simulated under the effects of blowing and suction. An earlier experimental study using hot-wire anemometry for a clean (no jet) NACA 2415 aerofoil at α = 8° shows a laminar separation bubble over the one-third of the airfoil upper surface. In the no jet case, the recently developed k-k L-ω and k-ω SST transition models accurately predict the location and extent of the separation bubble. Later, single or multiple jets with a width of 2.5% the chord length are placed on the aerofoil upper surface for simulating the isolated or simultaneous blowing and suction jets. For single jets with blowing or suction, whereas the k-ω SST model suppress the separation bubble in both cases, the k-k L-ω transition model doesn't completely eliminate the separation bubble but moves it downstream in the suction case. Overall, the blowing/suction control mechanism appears to be suppression of the separation bubble and reduction of the upper surface pressure to increase the lift and decrease the drag. For simultaneous blowing and suction, firstly, a blowing jet at 10%c and a suction jet at 36%c are placed at the beginning and end of the separation bubble based on the best results of the single jets. Then, the locations of the blowing and suction jets are reversed. In both cases, both transition models eliminate the separation bubble resulting in increase in the lift and decrease in the drag. However, the best results in terms of the L/D ratios are still obtained with the single suction jets. Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc.
Our aim was to evaluate the quality of life (QoL) in patients with ameloblastoma who had been treated by immediate mandibular reconstruction with a fibular free flap, and to analyse the association between QoL and their sociocultural and medical characteristics. We assessed the QoL outcomes of 33/45 patients using the University of Washington quality of life (UW-QoL) questionnaire and the 14-item Oral Health Impact Profile (OHIP-14). Thirty-three of the 45 questionnaires were returned (73%). In the UW-QoL the best-scoring domain was "shoulder", whereas the lowest scores were for "chewing" and "activity". In the OHIP-14 the lowest-scoring domain was "handicap", followed by "social disability" and "psychological discomfort". Mandibular reconstruction with a fibular free flap significantly influenced the patients' QoL and oral function. Their sociocultural data showed that most patients had a fairly low level of education.
In this study we propose a local-variable-based laminar-turbulence transition model that considers the effects of different
instability modes existing in highspeed aerodynamic flows. This model is validated with a number of available experiments
on transition including supersonic and hypersonic flows past straight/flared cones at small incidences and elliptic cones
at zero incidences. Computed results are in good agreement with experimental data.
Osteoradionecrosis of the mandible is a debilitating consequence of radiation therapy for head-and-neck malignancy. It can result in pain, bone exposure, fistula formation, and pathologic fracture. Recombinant human bone morphogenetic protein 2 (rhBMP-2) has shown promise in reconstruction of bone defects. The purpose of this study is to determine whether the addition of rhBMP-2 at the union of vascularized bone and native bone improves surgical outcomes in patients with osteonecrosis of the mandible.
This study was a retrospective analysis of patients who were treated between 2006 and 2010 for osteonecrosis of the mandible. Patients requiring definitive reconstruction after failure of a course of conservative management were included. Patients were divided into 2 cohorts depending on whether rhBMP-2 was used during the reconstruction. The primary outcome measure was defined as stable mandibular union.
Seventeen patients were included. The development of malunion was similar in both groups (13% for rhBMP-2 group vs 11% for non-rhBMP-2 group). Infectious complications were similar between the groups (25% in rhBMP-2 group vs 56% in non-rhBMP-2 group, P = .33). The rates of hardware removal were similar for the 2 groups (33% in non-rhBMP-2 group vs 25% in rhBMP-2 group, P = .10). No cancer recurrences were observed in patients receiving rhBMP-2.
The use of rhBMP-2 is safe in free flap reconstruction of the mandible, but its ability to significantly improve patient outcomes, as measured by rates of malunion, reoperation, or infection, is still unknown.
Osteoradionecrosis (ORN) is a severe complication of radiation therapy for head and neck cancer. The current theory in its pathophysiology is thought to be radiation-induced fibroatrophy of the bone. Location of primary tumor, stage of cancer, dose of radiation, oral hygiene, and smoking and alcohol use are risk factors in the development of ORN. Prevention is focused on thorough dental care before, during, and after radiation therapy. Treatment ranges from conservative management with oral rinses and local debridement to radical resection with microvascular free tissue transfer and reconstruction.
The University of Washington Quality of Life Scale (UW-QoL) is one of the most frequently reported health-related quality of life (HR-QoL) questionnaires in head and neck cancer, and since its first publication in 1993 has been used in many different cohorts. There is a considerable amount of information to assimilate and, to date, we know of no attempt that has been made to summarise publications specific to its use in a peer review journal. The aim of this review was to systematically search published papers that report its use, identify common themes, and present a tabulated summary. Several search engines were used (PubMed, Medline, Medical-Journals.com, eMedicine), and 222 abstracts were found and hand searched. A total of 66 papers were eligible for inclusion, 21 on functional outcome, 25 on predictors of HR-QoL, 19 on development or validation of the questionnaire, and one clinical trial. The review includes a diversity of studies and a range of HR-QoL outcomes following head and neck cancer. It provides clinicians and their colleagues in multidisciplinary teams with a source of quick reference to relevant papers reporting the UW-QoL, and gives a short summary of the pertinent conclusions drawn from each paper.
A model has been developed to incorporate more of the physics of free-stream turbulence effects into boundary layer calculations. the transport in the boundary layer is modeled using three terms: (1) the molecular viscosity, υ; (2) the turbulent eddy viscosity, εr, as used in existing turbulence models; and (3) a new free-stream-induced eddy viscosity, εf. The three terms are added to give an effective total viscosity. The free-stream-induced viscosity is modeled algebraically with guidance from experimental data. It scales on the rms fluctuating velocity in the free stream, the distance from the wall, and the boundary layer thickness. The model assumes a direct tie between boundary layer and free-stream fluctuations, and a distinctly different mechanism than the diffusion of turbulence from the free-stream to the boundary layer assumed in existing higher order turbulence models. the new model can be used in combination with any existing turbulence model. It is tested here in conjuction with a simple mixing length model and a parabolic boundary layer solver. Comparisons to experimental data are presented for flows with free-stream turbulence intensities ranging from 1 to 8% and for both zero and nonzero streamwise pressure gradient cases. Comparisons are good. Enhanced heat transfer in higher turbulence cases is correctly predicted. The effect of the free-stream turbulence on mean velocity and temperature profiles is also well predicted. In turbulent flow, the log region in the inner part of the boundary layer is preserved, while the wake is suppressed. The new model provides a simple and effective improvement for boundary layer prediction.
A unified approach that makes it possible to determine the extent and onset of transition in one calculation is presented. It treats the nonturbulent fluctuations in a manner similar to that used in describing turbulence. As a result, the complete flowfield can be calculated using existing computational fluid dynamics codes and without the use of stability codes. The method is validated by comparing the results for flat plates, airfoils, and infinite swept wings with available experiments. In general, good agreement is indicated.
Hypersonic boundary-layer measurements were conducted over a flared cone in a quiet wind tunnel. The flared cone was tested at a freestream unit Reynolds number of 2.82 x 10(6)/ft in a Mach 6 flow. This Reynolds number provided laminar-to-transitional bow over the model in a low-disturbance environment. Point measurements with a single hat wire using a novel constant voltage anemometry system were used to measure the boundary-layer disturbances. Surface temperature and schlieren measurements were also conducted to characterize the laminar-to-transitional state of the boundary layer and to identify instability modes. Results suggest that the second mode is the dominant mode of instability. The integrated growth rates of the second made compared well with linear stability theory in the linear stability regime. Furthermore, the existence of higher harmonics of the fundamental suggests that nonlinear disturbances are not associated with ''high'' freestream disturbance levels.
Existing transition models are surveyed and deficiencies in previous predictions, which seriously overestimate transition length under an adverse pressure gradient, are discussed. A new model for transition in an adverse pressure gradient situation is proposed and experimental results are provided which confirm its validity. A correlation for transition length is advanced which incorporates both Reynolds number and pressure gradient effects.
Under low free-stream turbulence conditions the basic mechanism of transition is laminar instability. There are, however, physical differences between zero and adverse pressure gradients. In the former case transition occurs randomly, due to the breakdown of laminar instability waves in sets. For an adverse pressure gradient the Tollmien-Schlichting waves appear more regularly with a well-defined spectral peak. As the adverse pressure gradient is increased from zero to the separation value the flow evolves continuously from random to periodic behavior and the dimensionless transition length progressively decreases.