Dynamic Inflow Research Articles

Asymmetries in an obstructed turbulent channel flow

The asymmetric flow pattern caused by a single thin-plate obstruction in a plane channel has been explored by means of direct numerical simulations. The blockage ratio was 1:2 and the bulk Reynolds number about 5700. In order to mimic an infinitely long channel section upstream of the obstruction, realistic dynamic inflow conditions were provided by a promising technique proposed by Barri et al. [“Inflow conditions for inhomogeneous turbulent flows,” Int. J. Numer. Methods Fluids 60, 227 (2009)]. The fluid downstream of the symmetric obstruction was sucked toward one side where a modestly long region of rather strong recirculating flow was observed. The weaker recirculation bubble formed at the opposite side was 17 times longer than the obstruction height and almost four times the size of the shorter bubble. The overall flow pattern turned out to be rather different from that observed in a similar study of channel flow subjected to periodically repeating obstructions by Makino et al. [“Turbulent structures and statistics in turbulent channel flow with two-dimensional slits,” Int. J. Heat Fluid Flow 29, 602 (2008)]. An anomalous variation of the pressure coefficient was observed with an excessively low pressure below the shorter of the bubbles. A locally high pressure occurred where the deflected jet flow impinges on the wall, whereas another pressure minimum could be associated with the flow acceleration caused by the severe blockage due to the major recirculation bubble. The turbulent fluctuations were suppressed due to the acceleration through the obstruction and high levels of streamwise velocity persisted far downstream. Exceptionally high turbulence levels were observed in the mixing-layers emanating from the two sides of the obstruction. The turbulence in these mixing-layers turned out to be qualitatively and quantitatively different on the two sides and exhibited distinctly different anisotropies.

Correlation study of a rotor in descending flight using DYMORE with a freewake model

In this work, the Blade Vortex Interaction (BVI) airloads characteristic for a rotor in descending flight condition is investigated using a nonlinear flexible multibody dynamics analysis code DYMORE. A free vortex wake model is incorporated into the comprehensive analysis system and improvement of airloads prediction as well as collective and cyclic pitch control settings is obtained over the finite-state dynamic inflow model that is adopted in the conventional DYMORE analysis. The three test conditions in the HART (Higher harmonic control Aeroacoustic Rotor Test) II are considered to illustrate the present investigation. It is found that the BVI airloads characteristic is significantly influenced by the higher harmonic pitch control inputs. The influence of BVI oscillatory peaks along with the miss-distance between the blade and the vortices is studied in detail to identify the mechanism of reducing noise and vibration in the HART II experiment.

Comprehensive Code Validation on Airloads and Aeroelastic Responses of the HART II Rotor

In this work, the comprehensive structural dynamics codes including DYMORE and CAMRAD II are used to validate the higher harmonic control aeroacoustic rotor test (HART) II data in descending flight condition. A total of 16 finite elements along with 17 aerodynamic panels are used for the CAMRAD II analysis; whereas, in the DYMORE analysis, 10 finite elements with 31 equally-spaced aerodynamic panels are utilized. To improve the prediction capability of the DYMORE analysis, the finite state dynamic inflow model is upgraded with a free vortex wake model comprised of near shed wake and trailed tip vortices. The predicted results on aerodynamic loads and blade motions are correlated with the HART II measurement data for the baseline, minimum noise and minimum vibration cases. It is found that an improvement of solution, especially for blade vortex interaction airloads, is achieved with the free wake method employed in the DYMORE analysis. Overall, fair to good correlation is achieved for the test cases considered in this study.

Nonlinear aeroelastic coupled trim and stability analysis of rotor-fuselage

Based on the Hamilton principle and the moderate deflection beam theory, discretizing the helicopter blade into a number of beam elements with 15 degrees of freedom, and using a quasi-steady aero-model, a nonlinear coupled rotor/fuselage equation is established. A periodic solution of blades and fuselage is obtained through aeroelastic coupled trim using the temporal finite element method (TEM). The Peters dynamic inflow model is used for vehicle stability. A program for computation is developed, which produces the blade responses, hub loads, and rotor pitch controls. The correlation between the analytical results and related literature is good. The converged solution simultaneously satisfies the blade and the vehicle equilibrium equations.

Advantages of fluorescence over diffuse reflectance measurements tested in phantom experiments with dynamic inflow of ICG

AbstractTime-resolved measurements of diffuse reflectance and fluorescence were carried out using phantom with dynamic inflow of indocyanine green (ICG) in tubes located at different depths. Better sensitivity of fluorescence signals related to the inflow of the dye was observed in comparison to simultaneously acquired diffuse reflectance. Obtained results can be referred to results of in-vivo measurements. We have observed much larger amplitude of changes in relative number of detected photons, mean time of flight and variance of the distributions of times of arrival of fluorescence photons than amplitudes of respective parameters measured from diffuse reflectance distributions of times of flight of photons. The constructed phantom allows us to study influence of concentration of the dye in the tube and the surrounding medium as well as temporal relation between appearance of the boli in deeper and superficial tube. Results of the study were used in optimization of the time-resolved multichannel system for simultaneous monitoring of fluorescence and reflectance.

Stall inception and its control in an axial flow fan under dynamic inflow distortion

The present experimental study demonstrates the effects of clean and distorted inflow conditions on the performance and nature of stall inception in a single stage axial flow fan. A 90° distortion screen located upstream of the rotor leading edge was rotated up to 40 per cent of the rotor speed in the clockwise (co-rotation) and counterclockwise (counter-rotation) directions to generate dynamic inflow distortion. It was observed that the stall margin deteriorated substantially under co-rotating inflow distortion as compared to counter-rotating inflow distortion. The degradation in stall margin was about 15 per cent and 1.98 per cent under co- and counter-rotating inflow distortions, respectively. Tip injection was used as a means of enhancing the fan performance under distorted inflow. With tip injection under co-rotating inflow distortion, about 2.8 per cent improvement in stall margin was observed. The improvement in stall margin under counter-rotating inflow distortion with tip injection was 2.98 per cent. The unsteady static pressure traces show clear differences in the nature of stall inception under co- and counter-rotating inflow distortions. The stall inception occurs through long-length-scale disturbances under co-rotating inflow distortion, while the mode of stall inception under clean flow and counter-rotating inflow distortions was through short-length-scale disturbances. The nature of stall inception under dynamic inflow distortion with tip injection remains the same as without tip injection.

Development of an Unsteady Aerodynamic Analysis Module for Rotor Comprehensive Analysis Code

The inherent aeromechanical complexity of a rotor system necessitated the comprehensive analysis code for helicopter rotor system. In the present study, an aerodynamic analysis module has been developed as a part of rotorcraft comprehensive program. Aerodynamic analysis module is largely classified into airload calculation routine and inflow analysis routine. For airload calculation, quasi-steady analysis model is employed based on the blade element method with the correction of unsteady aerodynamic effects. In order to take unsteady effects - body motion effects and dynamic stall - into account, aerodynamic coefficients are corrected by considering Leishman-Beddoes's unsteady model. Various inflow models and vortex wake models are implemented in the aerodynamic module to consider wake induced inflow. Specifically, linear inflow, dynamic inflow, prescribed wake and free wake model are integrated into the present module. The aerodynamic characteristics of each method are compared and validated against available experimental data such as Elliot's induced inflow distribution and sectional normal force coefficients of AH-1G. In order to validate unsteady aerodynamic model, 2-D unsteady model for NACA0012 airfoil is validated against aerodynamic coefficients of McAlister's experimental data.

Navier-Stokes Simulation of Unsteady Rotor-Airframe Interaction with Momentum Source Method

To numerically simulate aerodynamics of rotor-airframe interaction in a rigorous manner, we need to solve the Navier-Stokes system for a rotor-airframe combination as a whole. This often imposes a serious computational burden since rotating blades and a stationary body have to be simultaneously dealt with. An efficient alternative is to adopt a momentum source method in which the action of rotor is approximated as momentum source over a rotor disc plane in a stationary computational domain. This makes the simulation much simpler. For unsteady simulation, the instantaneous momentum sources are assigned only to a portion of disk plane corresponding to blade passage. The momentum source is obtained by using blade element theory with dynamic inflow model. Computations are carried out for the simple rotor-airframe model (the Georgia Tech model) and the results of the simulation are compared with those of the full Navier-Stokes simulation with moving mesh system for rotor and with experimental data. It is shown that the present simulation yields results as good as those of the full Navier-Stokes simulation.

A wake bending unsteady dynamic inflow model of tiltrotor in conversion flight of tiltrotor aircraft

The aerodynamics, dynamic responses and aeroelasticity of tiltrotor aircraft in the tilting of rotor i.e. in conversion flight are extraordinarily complicated. The traditional quasi-steady assumption model can not reflect the unsteady aerodynamic problems in the tilting of rotor. The CFD method based on the vortex theory can get better results, but it consumes a lot of computing resources. In this paper, a wake bending dynamic inflow model of tilting rotor was established firstly based on the Peters-He dynamic inflow model used in helicopter. Then combining with the ONERA unsteady aerodynamic model, a wake bending unsteady dynamic inflow model of tilting rotor in conversion flight of tiltrotor aircraft was established. The wake bending unsteady dynamic inflow model of tilting rotor was verified by using the experimental data of an isolated rotor model in large angle pitching up maneuver and was used to calculate the dynamic responses of tilting rotor in conversion flight of a tiltrotor aircraft model. The calculated results were analyzed to be physically reasonable.

Correction of the definition of mass flow parameter in dynamic inflow modelling

The dynamic inflow model, which has been extensively developed by Peters and his co-workers for the last two decades, is a powerful tool for predicting the induced velocity distribution over a rotor disc. Scant attention has, however, been paid so far in using the model to analyse an autorotative rotor. The authors identified a necessary change to the mass flow parameter of the original model of Peters for autorotating rotors. In response, questions were raised by readers about how the modified and original inflow parameters should consistently be explained, why the original model of Peters is insufficient for autorotation, and how the validity of the modified mass flow parameter can mathematically be enunciated. Indeed, the discussion in the article by Murakami and Houston (2008) was held in a manner that readers might have received an impression that the modified model was derived independently of the original model, and the connection to the original model was not clearly presented. This technical note is written with an aim to elucidate the mathematically consistent relationship between the original and modified mass flow parameters, and it is confirmed that the original definition of the mass flow parameter contains an error in its definition. It is concluded that the unified mass flow parameter, which is presented in this article, should always be used in the dynamic inflow model.

P-109 Mitral Valve Motion and Mitral Inflow Dynamics in Aortic Regurgitation, with Reference to the Relation with Regurgitant Jet Direction

(2.6±0.9 vs. 3.4±0.9 cm/s, P= 0.028) and longer interatrial time delay (33±25 vs. 12±19ms, P= 0.022). However, there were no differences in Va of RA and intra-atrial synchronicity between two groups. The lower mitral A velocity and prolonged inter-atrial time delay (OR, 95%CI: 1.12, 1.01 1.24 p = 0.025; 1.08, 1.01 1.16 p = 0.020 resp.) were the strongest predictors on presence of PAF. Conclusion: Compared to these without AF, pts with SND and PAF had worsening of LA mechanical function. The occurrence of inter-atrial dyssychrony may have implications to the mechanical benefit of alternative atrial pacing.

회전익기 통합해석프로그램을 위한 공력해석코드 개발

본 논문에서는 회전익기 통합해석프로그램개발의 일환으로 공력해석코드를 개발 및 검증하였다. 기본적인 공력하중은 익형 공력테이블을 이용한 깃요소이론을 기반으로 계산하였고, 로터의 유도 유입류를 계산하기 위해 선형유입류 모델, 동적유입류 모델, 지정후류모델, 자유후류 모델 등 여러 유입류 예측기법을 사용하였다. 각 모델의 특성을 파악하기 위해 Elliott 등의 유도 유입류 실험결과와 AH-1G 실험결과의 국소 수직력계수를 비교 및 검증하였다. In this study, an aerodynamic performance analysis code has been developed as a part of rotorcraft comprehensive program. Airloads on rotor blades are calculated based on the blade element theory with look-up tables of aerodynamic coefficients of 2-D airfoils. In order to calculate rotor induced inflow, various inflow prediction methods such as linear inflow, dynamic inflow, prescribed wake and free wake model are integrated into the present module. The aerodynamic characteristics of each method are compared and validated against available experimental data such as Elliot's inflow distribution and sectional normal force coefficients of AH-1G.

DIRECT CALCULATION OF THE RADIATIVE EFFICIENCY OF AN ACCRETION DISK AROUND A BLACK HOLE

Numerical simulation of magnetohydrodynamic (MHD) turbulence makes it possible to study accretion dynamics in detail. However, special effort is required to connect inflow dynamics (dependent largely on angular momentum transport) to radiation (dependent largely on thermodynamics and photon diffusion). To this end we extend the flux-conservative, general relativistic MHD code HARM from axisymmetry to full 3D. The use of an energy conserving algorithm allows the energy dissipated in the course of relativistic accretion to be captured as heat. The inclusion of a simple optically thin cooling function permits explicit control of the simulated disk's geometric thickness as well as a direct calculation of both the amplitude and location of the radiative cooling associated with the accretion stresses. Fully relativistic ray-tracing is used to compute the luminosity received by distant observers. For a disk with aspect ratio H/r ~ 0.1 accreting onto a black hole with spin parameter a/M = 0.9, we find that there is significant dissipation beyond that predicted by the classical Novikov-Thorne model. However, much of it occurs deep in the potential, where photon capture and gravitational redshifting can strongly limit the net photon energy escaping to infinity. In addition, with these parameters and this radiation model, significant thermal and magnetic energy remains with the gas and is accreted by the black hole. In our model, the net luminosi ty reaching infinity is 6% greater than the Novikov-Thorne prediction. If the accreted thermal energy were wholly radiated, the total luminosity of the accretion flow would be ~20% greater than the Novikov-Thorne value.

자동회전의 비정상 수치해법과 2차원 공력계수의 영향

전진 비행중인 자동회전 로터에 대한 비정상 수치해석 기법이 개발되었다. 자동회전 로터의 플래핑과 회전운동 방정식은 주어지는 시간간격에 따라 연속적으로 적분되며 이 때 회전면에서의 유도 속도장은 동적 유도흐름 이론(dynamic inflow theory)에 의해 계속 업데이트 되면서 블레이드의 모든 요소에서 유효 받음각을 결정하여 비정상 상태를 모사한다. 로터의 임의의 초기 회전속도 및 플래핑각에서 정상상태로 천이(transition)되는 과정을 시뮬레이션 하였고 블레이드 에어포일 공력 데이터들을 이용하여 방정식들의 수치해인 자동회전의 정상상태를 예측하였다. 2차원 Navier-Stokes 솔버로 받음각과 레이놀즈수에 따라 해석된 에어포일 데이터를 이용하여 자동회전의 비정상 시뮬레이션을 수행한 해석 결과는 풍동실험 결과와 잘 일치하였다 An unsteady numerical simulation method for an autorotating rotor in forward flight was developed. The flapping and rotational equations of motion of autorotation are continuously integrated for given time steps, meanwhile the induced velocity field at disc plane is obtained by the dynamic inflow theory embodying the unteadiness. The transitions from arbitrary initial states to equilibrium states were simulated. Steady autorotations as numerical solutions of equations were predicted by using two sources of blade airfoil data. The simulations using airfoil data which were obtained by a two dimensional Navier-Stokes solver in terms of angles of attack and Reynolds numbers have shown good agreements with wind tunnel experimental results.

513 ピッチ角制御時の水平軸風車の空力動特性の評価(OS7-3環境エネルギー関連の流体工学諸問題3)

513 ピッチ角制御時の水平軸風車の空力動特性の評価(OS7-3環境エネルギー関連の流体工学諸問題3)

How Dynamic Inflow Survives in the Competitive World of Rotorcraft Aerodynamics

How Dynamic Inflow Survives in the Competitive World of Rotorcraft Aerodynamics

2118 Contrast Inflow Dynamics MRA (CIDA) with automatic triggering:novel approach for ECG-gated dynamic contrast enhanced MRA

2118 Contrast Inflow Dynamics MRA (CIDA) with automatic triggering:novel approach for ECG-gated dynamic contrast enhanced MRA

Giant cardiac myxoma: Real-time characterization by 64-slice computed tomography

Video clip is available online. Video clip is available online. A 70-year-old woman was admitted at our institution because of recent onset of palpitations, dyspnea, and fatigue. On physical examination, she appeared well and she did not present particular signs except for a pulse rate of 114 beats per minute; her blood pressure was 155/85 mm Hg, axillary temperature was 36.7°C, respirations were 16 breaths per minute, and arterial blood gas measurements were normal. The chemistry and hematologic laboratory values were within the normal reference ranges. Electrocardiography revealed sinus tachycardia at a rate of 115 beats per minute and diphasic P waves in leads II, aVF, and V3 through V5. A chest radiography showed no abnormalities of the heart and mediastinum, and the lungs were clear. However, in the lateral view, an egg-shaped image corresponding to the atria was present and appeared highly suspicious for an intracardiac mass. A transthoracic echocardiographic examination disclosed a dilated left atrium (60 × 40 mm) filled almost entirely by a mobile, pedunculated mass of echoes, 2.7 by 7 cm, that partially prolapsed into the left ventricle during diastole with an incomplete closure of the mitral valve leaflets and an associated jet of mild regurgitation (Figure 1). The mass was highly mobile and appeared to be attached to the interatrial septum by a large stalk (2 cm). Transesophageal echocardiogram was impracticable because of the presence of Zenker's diverticulum. A 64-slice contrast-enhanced computed tomography (LightSpeed VCT, GE Healthcare, Milwaukee, Wis) was performed to confirm the diagnosis. Multiplanar reconstructions exactly defined the tumor attachment in the angle between the upper portion of interatrial septum and the left atrial roof (Figure 1). Functional and dynamic features were obtained by 3-dimensionally rendered real-time reconstructions (Aquarius, Tera Recon, San Mateo, Calif) that demonstrated this huge mass prolapsing through the mitral orifice and greatly reducing the diastolic filling of the left ventricle (Video 1). The patient had an urgent operation. Because of the large dimensions and the site of implant, we preferred a biatrial approach; thus the resection was accomplished in a “septal superior approach fashion.” Actually, by direct visualization, the mass presented a large stalk localized in the upper interatrial septum and widely extending to the roof of the left atrium. The tumor was extracted en bloc, and gross inspection showed a huge trilobulated mass measuring about 4 × 7 × 3 cm with a stalk of 2 × 2 cm (Figure 2). Fresh section revealed a reddish mass with diffuse hemorrhagic infiltration strongly suggestive of cardiac myxoma. Once the mass had been removed, the mitral apparatus was carefully inspected for possible valve incompetence that was preoperatively undetectable. However, the saline solution injection revealed only a trivial central regurgitation not susceptible of surgical correction. The procedure was completed as usual without complications, and the postoperative course was uneventful except for the occurrence of a junctional rhythm, which spontaneously resolved in the third postoperative day. Histology confirmed the diagnosis of myxoma. Usually pedunculated, cardiac myxomas develop in the atria in about 90% of the cases (75% left atrium and 15% to 20% right atrium). Left atrial myxomas originate from the interatrial septum in 85% of the cases (mostly from the fossa ovalis), with the others usually arising from the posterior or anterior atrial wall.1Reyen K. Cardiac myxomas.N Engl J Med. 1995; 333: 1610-1617Crossref PubMed Scopus (996) Google Scholar Giant cardiac myxomas have also been reported in the literature, and when sited in the left atrium, they can give rise to critical drawbacks for diagnosis of coexistent or subsequent mitral valve disease.2Davoli G. Muzzi L. Lucchese G. Uricchio N. Chiavarelli M. Large left atrial myxoma with severe mitral valve regurgitation. The inverted T-shaped biatrial incision revisited.Tex Heart Inst J. 2006; 33: 51-53PubMed Google Scholar Multislice computed tomography is emerging as a useful adjunctive tool in cardiovascular imaging, capable of supplying an extremely accurate, operator-independent definition of anatomic and functional details.3Feuchtner G. Mueller S. Bonatti J. Friedrich G. zur Nedden D. Smekal A. Prolapsing atrial myxoma. Dynamic visualization with multislice computed tomography.Circulation. 2004; 109: e165-e166Crossref PubMed Google Scholar Its great diagnostic power can sometimes cause this technique to be used inappropriately. In our experience, precisely identifying the unusual tumor attachment resulted in a fundamental diagnostic implement for the choice of surgical approach, which is crucial to achieve a radical excision, to avoid the risk of tumor fragmentation (especially for huge myxomas), and to manage a possibly associated valve disease.2Davoli G. Muzzi L. Lucchese G. Uricchio N. Chiavarelli M. Large left atrial myxoma with severe mitral valve regurgitation. The inverted T-shaped biatrial incision revisited.Tex Heart Inst J. 2006; 33: 51-53PubMed Google Scholar Download .mpg (1.29 MB) Help with mpg files Video 1Three-dimensionally rendered real-time reconstruction showing the dynamic mitral inflow obstruction by the tumor.

Guest Editorial

This special issue on Wind Energy contains a collection of contributions covering a variety of topics providing an indication on the research and development trends wind energy underwent last year. Most of the contributions originate from presentations made during the January 2007 ASME Wind Symposium in the United States of America and the European Wind Energy Conference.At machine level, as expected, there is a strong participation of aerodynamics and its companion, aeroelasticity. Progress in this direction is of major importance for the reliability of wind turbines especially when access to the machine is difficult as in offshore installations. Also important is the performance aspect, which is directly linked to costs. In this connection, control can provide great help by allowing either reduction of loads or increase of the energy capture at the same level of loads. The connection of loads to reliability either in terms of extremes or fatigue concludes this thematic area. In aerodynamics, open questions concerning dynamic inflow, stall, and 3D flow evolution, in particular, at stand still, are being considered and progress is reported mainly in terms of modeling. With respect to control, performance aspects of the variable speed concept also in combination to pitch variation are analyzed. Finally, in terms of loads, the present contributions focus on the assessment of the setup in terms of extremes, modeling of the turbulent inflow, and the joint wind-wave effect on offshore installations.At resource level, two important aspects are considered: The first concerns site assessment and the option of speeding up the process by means of numerical simulations and the issue of analyzing the uncertainties connected to measurements. They are both of particular interest for investors and developers. Progress in this direction is expected to further promote the use of wind energy by reducing investment risks.In recent years, interest in wind energy applications has expanded to less friendly sites as compared to earlier practice. Offshore installations as well as projects in remote areas have revealed the necessity of condition monitoring. The experience from such a project together with recommendations is reported. Again, this is a topic of particular interest for developers.Following the history of wind energy progress, it is clear that the sector is undergoing a fast transformation in all aspects. In terms of research, in addition to the existing open questions, the clear trend for larger wind turbines will bring in new problems. At present, the typical commercial size is at 2.5–3MW, while today there are operating designs up to 5MW. Improving the design and at the same time increasing the reliability of the machines will be the main challenges for the next generation of wind turbines. It will involve research on materials, aerodynamic design, power and load control, development of multiphysics simulation procedures, etc. Similarly at the developers’ level, aspects such as site assessment and condition monitoring, more accurate procedures will be needed. Also research on developing faster manufacturing procedures will be needed. The fast market expansion worldwide, with a strong participation of China and India, will increase the demand rendering the already supply shortage more severe. In conclusion, the future for the wind energy sector is promising with the research community having a particular role. We hope that the present issue of JSEE is contributing to this perspective.Closing this editorial note, I would like first to sincerely thank the authors and reviewers for working concurrently to complete the review process for this issue. I would also like to thank Patrick Moriarty from NREL and Takis Chaviaropoulos from CRES for their assistance in recruiting papers from the ASME and the EWEA conferences.

Determination of the angle of attack on rotor blades

AbstractTwo simple methods for determining the angle of attack (AOA) on a section of a rotor blade are proposed. Both techniques consist of employing the Biot–Savart integral to determine the influence of the bound vorticity on the velocity field. In the first technique, the force distribution along the blade and the velocity at a monitor point in the vicinity of the blade are assumed to be known from experiments or CFD computations. The AOA is determined by subtracting the velocity induced by the bound circulation, determined from the loading, from the velocity at the monitor point. In the second method, the full pressure distribution on the blade is assumed to be known and used to determine the local distribution of circulation along the surface contour of the blade. Using the local distribution of circulation to determine the influence of the bound vorticity enables the velocity monitor points to be located closer to the blade, and thus to determine the AOA with higher accuracy. Data from CFD computations for flows past the Tellus 95 kW wind turbine at different wind speeds are used to test both techniques. Comparisons show that the proposed methods are in good agreement with existing techniques. The advantage of the proposed techniques, as compared with existing techniques, is that they can be used to determine the AOA on rotor blades under general flow conditions (e.g. operations in yaw or with dynamic inflow). Copyright © 2008 John Wiley & Sons, Ltd.