Transition and separation control in the leading edge region

2001 ◽  
Vol 105 (1049) ◽  
pp. 371-378
Author(s):  
P. W. C. Wong ◽  
M. Maina ◽  
A. M. Cobbin
Keyword(s):  
Parametric Study ◽  
Effective Means ◽  
Leading Edge ◽  
Peak Height ◽  
Edge Region ◽  
Military Aircraft ◽  
Laminar Separation ◽  
Pressure Distributions ◽  
Crossflow Instability ◽  
And Control

Abstract This paper describes an investigation of methods of controlling transition and separation in the leading edge region of military aircraft wings. For wings with the high leading edge sweep relevant to some military aircraft, if attachment line contamination can be prevented then transition is predominantly caused by crossflow instability close to the leading edge. The use of surface suction or cooling for suppressing these instabilities in order to delay transition, has been investigated in a parametric study. The placing of a short suction panel close to the leading edge has been found to be an effective means of controlling instability. Conversely, the level of cooling required to suppress crossflow instability may be too high for practical aircraft applications. The use of suction for preventing laminar separation for pressure distributions with a leading edge suction peak has also been included in the parametric study. The suction quantity required is strongly dependent on the peak height. The suction quantity that can be achieved in practice will limit the maximum peak height that can be attained without laminar separation. An investigation of leading edge stall and control has also been carried out. The analysis suggests that it is important to be able to identify whether the stall is due to laminar bubble bursting or turbulent re-separation, since different methods of controlling the stall may be required.

scholarly journals Boundary Layer and Navier-Stokes Analysis of a NASA Controlled-Diffusion Compressor Blade

1990 ◽  
Author(s):  
Y. K. Ho ◽  
G. J. Walker ◽  
P. Stow
Keyword(s):  
Boundary Layer ◽  
Turbulence Modeling ◽  
Separation Bubble ◽  
Leading Edge ◽  
Adverse Pressure Gradient ◽  
Compressor Blade ◽  
Navier Stokes ◽  
Laminar Separation ◽  
Controlled Diffusion ◽  
Pressure Distributions

Performance calculations for a NASA controlled-diffusion compressor blade have been carried out with a coupled inviscid-boundary layer code and a time-marching Navier-Stokes solver. Comparisons with experimental test data highlight and explain the strengths and limitations of both these computational methods. The boundary layer code gives good results at and near design conditions. Loss predictions however deteriorated at off-design incidences. This is mainly due to a problem with leading edge laminar separation bubble modelling; coupled with an inability of the calculations to grow the turbulent boundary layer at a correct rate in a strong adverse pressure gradient. Navier-Stokes loss predictions on the other hand are creditable throughout the whole incidence range, except at extreme positive incidence where turbulence modeling problems similar to those of the coupled boundary layer code are observed. The main drawback for the Navier-Stokes code is the slow rate of convergence for these low Mach number cases. Plans are currently under review to address this problem. Both codes give excellent predictions of the blade surface pressure distributions for all the cases considered.

Aerodynamic performance investigation of sweptback wings with bio-inspired leading-edge tubercles

2021 ◽  
Author(s):  
V. T. Gopinathan ◽  
J. Bruce Ralphin Rose
Keyword(s):  
Flow Control ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Aerodynamic Performance ◽  
Laminar Separation ◽  
Flow Separation Control ◽  
Pressure Distributions ◽  
Lifting Surfaces ◽  
Naca 0015

The aerodynamic behavior of sweptback wing configurations with bio-inspired humpback whale (HW) leading-edge (LE) tubercles has been investigated through computational and experimental techniques. Specifically, the aerodynamic performance of tubercled wings with symmetric (NACA 0015) and cambered (NACA 4415) airfoils is validated against the baseline model at various angles of attack ([Formula: see text]. The [Formula: see text]/[Formula: see text] ratio of the HW flipper is strategically reduced to 0.15 for ascertaining the flow control potential of the bio-inspired wings with sweptback configuration. It is a novel effort to quantify the effect of the leading-edge protuberances on stall delay, flow separation control and distribution of streamline vortices at unique [Formula: see text]/[Formula: see text] ratio outside the thickness range of HW flipper morphology. Four tapered sweptback wing models (Baseline A, Baseline B, HUMP 0015, HUMP 4415) are used with the amplitude-to-wavelength ([Formula: see text] ratio of 0.24 and Reynolds number about [Formula: see text]. The chordwise pressure distributions are recorded at the peak, mid and trough regions of the tubercled wings through a detailed wind tunnel testing and validated with numerical analysis. Additionally, the flow characteristics over the bio-inspired surfaces have been qualitatively analyzed through the laser flow visualization (LFV) technique to reveal the influence of laminar separation bubbles (LSBs). The essential aerodynamic characteristics such as boundary layer trip delay, vortex mixing, stall delay, and flow control at different AoA are addressed through consistent experimental data. As the sweptback configuration is a primary choice for airplane wings, the improved aerodynamic characteristics of the tubercled wings can be effectively utilized for the design of novel lifting surfaces, hydroplanes and wind turbines in the near future.

Investigation on the effect of leading edge tubercles of sweptback wing at low reynolds number

2020 ◽  
Vol 21 (6) ◽  
pp. 621
Author(s):  
Veerapathiran Thangaraj Gopinathan ◽  
John Bruce Ralphin Rose ◽  
Mohanram Surya
Keyword(s):  
Leading Edge ◽  
Reynolds Numbers ◽  
Sweep Angle ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Flow Energy ◽  
Airplane Wing ◽  
Low Reynolds ◽  
Naca 0015 ◽  
Wing Performance

Aerodynamic efficiency of an airplane wing can be improved either by increasing its lift generation tendency or by reducing the drag. Recently, Bio-inspired designs have been received greater attention for the geometric modifications of airplane wings. One of the bio-inspired designs contains sinusoidal Humpback Whale (HW) tubercles, i.e., protuberances exist at the wing leading edge (LE). The tubercles have excellent flow control characteristics at low Reynolds numbers. The present work describes about the effect of tubercles on swept back wing performance at various Angle of Attack (AoA). NACA 0015 and NACA 4415 airfoils are used for swept back wing design with sweep angle about 30°. The modified wings (HUMP 0015 A, HUMP 0015 B, HUMP 4415 A, HUMP 4415 B) are designed with two amplitude to wavelength ratios (η) of 0.1 & 0.24 for the performance analysis. It is a novel effort to analyze the tubercle vortices along the span that induce additional flow energy especially, behind the tubercles peak and trough region. Subsequently, Co-efficient of Lift (CL), Co-efficient of Drag (CD) and boundary layer pressure gradients also predicted for modified and baseline (smooth LE) models in the pre & post-stall regimes. It was observed that the tubercles increase the performance of swept back wings by the enhanced CL/CD ratio in the pre-stall AoA region. Interestingly, the flow separation region behind the centerline of tubercles and formation of Laminar Separation Bubbles (LSB) were asymmetric because of the sweep.

Heat Transfer and Flowfield Measurements in the Leading Edge Region of a Stator Vane Endwall

1999 ◽  
Vol 121 (3) ◽  
pp. 558-568 ◽  
Author(s):  
M. B. Kang ◽  
A. Kohli ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Edge Region ◽  
Leading Edge Vortex ◽  
Stator Vane ◽  
Edge Vortex ◽  
The Mean

The leading edge region of a first-stage stator vane experiences high heat transfer rates, especially near the endwall, making it very important to get a better understanding of the formation of the leading edge vortex. In order to improve numerical predictions of the complex endwall flow, benchmark quality experimental data are required. To this purpose, this study documents the endwall heat transfer and static pressure coefficient distribution of a modern stator vane for two different exit Reynolds numbers (Reex = 6 × 105 and 1.2 × 106). In addition, laser-Doppler velocimeter measurements of all three components of the mean and fluctuating velocities are presented for a plane in the leading edge region. Results indicate that the endwall heat transfer, pressure distribution, and flowfield characteristics change with Reynolds number. The endwall pressure distributions show that lower pressure coefficients occur at higher Reynolds numbers due to secondary flows. The stronger secondary flows cause enhanced heat transfer near the trailing edge of the vane at the higher Reynolds number. On the other hand, the mean velocity, turbulent kinetic energy, and vorticity results indicate that leading edge vortex is stronger and more turbulent at the lower Reynolds number. The Reynolds number also has an effect on the location of the separation point, which moves closer to the stator vane at lower Reynolds numbers.

Neurotechnology as a factor of the educational process transformation

2021 ◽  
pp. 98-13
Author(s):  
Л.Д. Александрова ◽  
Р.А. Богачева ◽  
Т.А. Чекалина ◽  
М.В. Максимова ◽  
В.И. Тимонина
Keyword(s):  
Effective Means ◽  
Individual Characteristics ◽  
Educational Process ◽  
Special Equipment ◽  
Research Areas ◽  
Long Time ◽  
Mental Abilities ◽  
The Individual ◽  
And Control

Изучение возможностей мозга для повышения качества обучения находится в центре внимания педагогической науки уже много лет. Развитие цифровизации позволило использовать в исследованиях специальное оборудование, с помощью которого можно оценивать и контролировать работу мозга, развивать умственные способности, познавательные функции и т. п. Нейротехнологии стали эффективным средством, позволяющим трансформировать образовательный процесс за счет подбора специального учебного контента с учетом индивидуальных особенностей обучающихся. Вместе с тем возникает необходимость в конкретизации терминологии и определении актуальных направлений исследований в данной области. For a long time, the study of the brain capabilities for the improvement of the quality of education has been an urgent direction in pedagogical science. Due to the development of digitalization, new areas of research have emerged related to the use of special equipment that makes it possible to assess and control brainwork, develop mental abilities, cognitive functions, etc. One of them is neurotechnology, which is an effective means of transforming the educational process: it offers educational content based on the individual characteristics of students. Thus, a need to concretize the terminology and determine the current research areas arises. The article aims to attempt to fill this gap with the help of a representative analysis of publications on neurotechnologies, as well as the essence of neuroeducation.

Influence of Anisotropic Thermal Conductivity on Overall Cooling Effectiveness on a Film Cooled Leading Edge

2021 ◽  
pp. 1-22
Author(s):  
Carol Bryant ◽  
James L. Rutledge
Keyword(s):  
Thermal Conductivity ◽  
Temperature Distribution ◽  
Film Cooling ◽  
Leading Edge ◽  
Ceramic Matrix Composites ◽  
Internal Cooling ◽  
Matrix Composites ◽  
Edge Region ◽  
Turbine Engine ◽  
Anisotropic Thermal Conductivity

Abstract Increasing interest in the use of ceramic matrix composites (CMCs) for gas turbine engine hot gas path components requires a thorough examination of the thermal behavior one may expect of such components. Their highly anisotropic thermal conductivity is a substantial departure from traditional metallic components and can influence the temperature distribution in surprising ways. With the ultimate surface temperature dependent upon the internal cooling scheme, including cooling from within the film cooling holes themselves, as well as the external film cooling, the relative influence of these contributions to cooling can be affected by the directionality of the thermal conductivity. Conjugate heat transfer computational simulations were performed to evaluate the effect of anisotropy in the leading edge region of a turbine component. The leading edge region is modeled as a fully film-cooled half cylinder with a flat afterbody. The anisotropic directionality of the thermal conductivity is shown to have a significant effect on the temperature distribution over the surface of the leading edge. While structural considerations with CMC components are often paramount, designers should be aware of the thermal ramifications associated with the selection of the CMC layup.

Analysis on the effect of polyetherimide on energy distribution of radio frequency heating of viscous sauce

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Huojie Shi ◽  
Hui Chen ◽  
Zhiming Yan
Keyword(s):  
Energy Distribution ◽  
Radio Frequency ◽  
Peanut Butter ◽  
Effective Means ◽  
Commercial Application ◽  
Rf Heating ◽  
Heating Uniformity ◽  
Uneven Heating ◽  
And Control ◽  
Shape And Size

Abstract Radio frequency (RF) sterilization of low-moisture, high-oil, high-protein, and viscous sauces for instant food (LHHVS) demonstrates many advantages, but uneven heating is a main problem that must be addressed. Main factors that affect heating uniformity are generally considered dielectric properties, shape and size of the sample and its position relative to the electrode plate, in addition the structure and voltage of RF electrode. A method based on texture characteristics of the solid–gel–liquid mixing system of LHHVS for adjustment and control of energy distribution in the RF field is proposed in this study to improve the heating uniformity. First, energy conversion principles and control equations of RF heating were analyzed on the basis of dielectric theory. Second, the influence of RF electromagnetic field-medium polyetherimide (PEI) on the RF heating of peanut butter (RHPB) was investigated on the basis of the numerical model of RHPB that was verified through experiments. Finally, the influence mechanism and its regulation and control effect were analyzed and discussed. The following conclusions can be drawn from this study: the increase of electrode gaps exerts minimal effect although it reduces the unevenness of the energy distribution. However, RF heating protocols must use the smallest possible electrode gap to heat agrifoods and increase the heating rate significantly. The energy distribution on the part of the sample close to PEI varies with the change of geometry and size of PEI when its placement is bias or symmetric. The area of energy enhancement continues to expand where the sample is in contact with PEI as PEI gradually increases. The area where the temperature increases under the influence of PEI will expand along the direction of the sample radius when the thickness of PEI remains unchanged and the radius gradually enlarges; otherwise, it will expand along the direction of the sample thickness. The influence of PEI on the energy distribution of RHPB demonstrates local characteristics. PEI significantly influences the energy distribution and heating mode of RHPB, which is easy to adjust and control, but does not reduce the processing speed and does not increases energy consumption. Hence, PEI is an effective means to interfere with energy distribution of RHPB. Uniform energy distribution can be obtained by selecting the appropriate PEI shape and size. Results of this study can help determine the experimental protocol for RHPB with the optimal uniform distribution and promote the fast commercial application of this technology.

Measurements of Secondary Flows Downstream of a Turbine Cascade at Off-Design Incidence

2004 ◽  
Author(s):  
M. W. Benner ◽  
S. A. Sjolander ◽  
S. H. Moustapha
Keyword(s):  
Large Scale ◽  
Prediction Method ◽  
Leading Edge ◽  
Field Measurements ◽  
Inviscid Flow ◽  
Secondary Flows ◽  
Subsequent Paper ◽  
Empirical Prediction ◽  
Pressure Distributions ◽  
Passage Vortex

This paper presents experimental results of the secondary flows from two large-scale, low-speed, linear turbine cascades for which the incidence was varied. The aerofoils for the two cascades were designed for the same inlet and outlet conditions and differed mainly in their leading-edge geometries. Detailed flow field measurements were made upstream and downstream of the cascades and static pressure distributions were measured on the blade surfaces for three different values of incidence: 0, +10 and +20 degrees. The results from this experiment indicate that the strength of the passage vortex does not continue to increase with incidence, as would be expected from inviscid flow theory. The streamwise acceleration within the aerofoil passage seems to play an important role in influencing the strength of the vortex. The most recent off-design secondary loss correlation (Moustapha et al. [1]) includes leading-edge diameter as an influential correlating parameter. The correlation predicts that the secondary losses for the aerofoil with the larger leading-edge diameter are lower at off-design incidence; however, the opposite is observed experimentally. The loss results at high positive incidence have also high-lighted some serious shortcomings with the conventional method of loss decomposition. An empirical prediction method for secondary losses has been developed and will be presented in a subsequent paper.

Anti-Interference Optimal Design of Grain Combine Harvester Multiple Target Working Speed Control Model

2013 ◽  
Vol 753-755 ◽  
pp. 1382-1385
Author(s):  
Xin Wang ◽  
Han Fu ◽  
Du Chen ◽  
Shu Mao Wang
Keyword(s):  
Effective Means ◽  
Optimization Theory ◽  
Multiple Control ◽  
Power Cost ◽  
High Productivity ◽  
Key Factor ◽  
Objective Control ◽  
Combine Harvester ◽  
And Control ◽  
Measurement And Control

Harvesting speed is a key factor that influences working quality, utilization and harvest efficiency of the working process of grain combine harvester. In order to solve multi-objective control and poor anti-interference ability of measurement system in combine harvester, this paper uses optimization theory and error analysis theory to integrate analyze multi-source disturbance of data which is acquired in measurement and control system. The optimum working state control algorithm which proposes by this paper has better robust and anti-interference features, and what is more, it can be targeted by low yield loss, high productivity and low power cost. It provides theoretical basis and data support for the domestic agricultural harvesting machine, which also is an effective means to heighten the automatic level of the agricultural information technology. Keywords: Grain Combine harvester; Multiple control strategy; Anti-interference ability

Comparison of RANS and DES Modeling Against Measurements of Leading Edge Film Cooling on a First-Stage Vane

2016 ◽  
Author(s):  
S. Ravelli ◽  
G. Barigozzi
Keyword(s):  
Film Cooling ◽  
Guide Vane ◽  
Leading Edge ◽  
Spanwise Direction ◽  
Intensity Level ◽  
Edge Region ◽  
Cooling Effectiveness ◽  
Stagnation Line ◽  
Film Cooling Effectiveness ◽  
Adiabatic Effectiveness

The performance of a showerhead arrangement of film cooling in the leading edge region of a first stage nozzle guide vane was experimentally and numerically evaluated. A six-vane linear cascade was tested at an isentropic exit Mach number of Ma2s = 0.42, with a high inlet turbulence intensity level of 9%. The showerhead cooling scheme consists of four staggered rows of cylindrical holes evenly distributed around the stagnation line, angled at 45° towards the tip. The blowing ratios tested are BR = 2.0, 3.0 and 4.0. Adiabatic film cooling effectiveness distributions on the vane surface around the leading edge region were measured by means of Thermochromic Liquid Crystals technique. Since the experimental contours of adiabatic effectiveness showed that there is no periodicity across the span, the CFD calculations were conducted by simulating the whole vane. Within the RANS framework, the very widely used Realizable k-ε (Rke) and the Shear Stress Transport k-ω (SST) turbulence models were chosen for simulating the effect of the BR on the surface distribution of adiabatic effectiveness. The turbulence model which provided the most accurate steady prediction, i.e. Rke, was selected for running Detached Eddy Simulation at the intermediate value of BR = 3. Fluctuations of the local temperature were computed by DES, due to the vortex structures within the shear layers between the main flow and the coolant jets. Moreover, mixing was enhanced both in the wall-normal and spanwise direction, compared to RANS modeling. DES roughly halved the prediction error of laterally averaged film cooling effectiveness on the suction side of the leading edge. However, neither DES nor RANS provided the expected decay of effectiveness progressing downstream along the pressure side, with 15% overestimation of ηav at s/C =0.2.

Sign in / Sign up

Export Citation Format

Share Document