Passive Drag Reduction Technology Using Microfiber Coatings

Mapping Intimacies ◽

10.1115/fedsm2021-61461 ◽

2021 ◽

Author(s):

Mitsugu Hasegawa ◽

Hirotaka Sakaue

Keyword(s):

Drag Reduction ◽

Bluff Body ◽

Separated Flow ◽

Cylinder Surface ◽

Cylinder Diameter ◽

Trailing Edges ◽

Engineered Surfaces ◽

Long Fibers ◽

The Impact ◽

Influential Parameters

Abstract Engineered surfaces and coatings can passively manipulate flow over a bluff-body without significant retrofitting and are of great technological interest for a broad range of applications in the engineering field. A microfiber coating with a hair-like structure is developed and studied as a passive drag reduction method for flow over a cylinder that features both attached and separated flow. The impact of the microfiber coating on drag is experimentally investigated at a Reynolds number of 6.1 × 104 based on the cylinder diameter. Microfiber coatings of various lengths between 1.1% and 8.0% of the cylinder diameter are fabricated using flocking technology and applied to various positions on the cylinder surface between the leading and trailing edges. It is shown that the microfiber length and location are both influential parameters in drag reduction. Two types of drag reduction can be seen depending on the location of the microfiber coating: (1) Drag is reduced significantly if the microfiber coating is applied before flow separates over the cylinder (2) Drag is reduced moderately if the microfiber coating is applied after the point of flow separation on the cylinder. The former case’s best performance is achieved with a microfiber length of less than 1.8% of the cylinder diameter. The latter case shows better performance with relatively long fibers, where the microfiber’s length is greater than 3.3% of the cylinder diameter.

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Microfiber Coating for Flow Control over a Blunt Surface

Coatings ◽

10.3390/coatings9100664 ◽

2019 ◽

Vol 9 (10) ◽

pp. 664 ◽

Cited By ~ 1

Author(s):

Mitsugu Hasegawa ◽

Hirotaka Sakaue

Keyword(s):

Drag Reduction ◽

Flow Control ◽

Bluff Body ◽

Relative Length ◽

Control Device ◽

Cylinder Surface ◽

Passive Flow Control ◽

Passive Flow ◽

Maximum Drag Reduction ◽

The Impact

A microfiber coating having a hair-like structure is investigated as a passive flow control device of a bluff body. The effect of microfiber length is experimentally studied to understand the impact of the coating on drag on a cylinder. A series of microfiber coatings with different lengths are fabricated using flocking technology and applied to various locations over the cylinder surface under the constant Reynolds number of 6.1 × 104 based on the diameter of the cylinder. It is found that the length and the location both play important roles in the drag reduction. Two types of drag reduction can be seen: (1) when the relative length of the microfiber, k/D, is less than 1.8%, and the coating is applied before flow separates over the cylinder; and (2) k/D is over 3.3%, and the coating is applied after the flow separation location on the cylinder. The maximum drag reduction for the former type is 59% compared to that from the cylinder without the microfiber coating. For the latter type, the maximum drag reduction is 27%.

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Drag reduction by closed-loop control of a separated flow over a bluff body with a blunt trailing edge

Proceedings of the 44th IEEE Conference on Decision and Control ◽

10.1109/cdc.2005.1582204 ◽

2006 ◽

Cited By ~ 14

Author(s):

L. Henning ◽

R. King

Keyword(s):

Drag Reduction ◽

Bluff Body ◽

Closed Loop ◽

Separated Flow ◽

Closed Loop Control ◽

Trailing Edge ◽

Loop Control ◽

Blunt Trailing Edge

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On the steady separated flow around an inclined flat plate

Journal of Fluid Mechanics ◽

10.1017/s0022112096004247 ◽

1997 ◽

Vol 333 ◽

pp. 403-413 ◽

Cited By ~ 7

Author(s):

W. W. H. YEUNG ◽

G. V. PARKINSON

Keyword(s):

Flat Plate ◽

Bluff Body ◽

Separation Bubble ◽

Separated Flow ◽

Leading Edge ◽

Source Model ◽

Pressure Distributions ◽

Wide Range ◽

Trailing Edges ◽

Edge Separation

An inviscid analytic model is proposed for the steady separated flow around an inclined flat plate. With the plate normal to the stream, the model reduces to the wake-source model of Parkinson & Jandali originally developed for flow external to a symmetrical two-dimensional bluff body and its wake. At any other inclination, the Kutta condition is satisfied at both leading and trailing edges of the plate, and, in the limit that the angle of attack approaches zero, classical airfoil theory is recovered. A boundary condition is formulated based on some experimental results of Abernathy, but no additional empirical information is required. The predicted pressure distributions on the wetted surface for a wide range of angle attack are found to be in good agreement with experimental data, especially at smaller angles of attack. An extension to include a leading-edge separation bubble is explored and results are satisfactory.

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Numerical analysis of high-lift configurations with oscillating flaps

CEAS Aeronautical Journal ◽

10.1007/s13272-021-00498-7 ◽

2021 ◽

Author(s):

Johannes Ruhland ◽

Christian Breitsamter

Keyword(s):

Reynolds Number ◽

Flow Separation ◽

Separated Flow ◽

Navier Stokes ◽

Rotational Axis ◽

High Lift ◽

Hinge Point ◽

Reduced Frequency ◽

Flap Deflection ◽

The Impact

AbstractThis study presents two-dimensional aerodynamic investigations of various high-lift configuration settings concerning the deflection angles of droop nose, spoiler and flap in the context of enhancing the high-lift performance by dynamic flap movement. The investigations highlight the impact of a periodically oscillating trailing edge flap on lift, drag and flow separation of the high-lift configuration by numerical simulations. The computations are conducted with regard to the variation of the parameters reduced frequency and the position of the rotational axis. The numerical flow simulations are conducted on a block-structured grid using Reynolds Averaged Navier Stokes simulations employing the shear stress transport $$k-\omega $$ k - ω turbulence model. The feature Dynamic Mesh Motion implements the motion of the oscillating flap. Regarding low-speed wind tunnel testing for a Reynolds number of $$0.5 \times 10^{6}$$ 0.5 × 10 6 the flap movement around a dropped hinge point, which is located outside the flap, offers benefits with regard to additional lift and delayed flow separation at the flap compared to a flap movement around a hinge point, which is located at 15 % of the flap chord length. Flow separation can be suppressed beyond the maximum static flap deflection angle. By means of an oscillating flap around the dropped hinge point, it is possible to reattach a separated flow at the flap and to keep it attached further on. For a Reynolds number of $$20 \times 10^6$$ 20 × 10 6 , reflecting full scale flight conditions, additional lift is generated for both rotational axis positions.

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Computational Fluid Dynamic Applications for Jet Propulsion System Integration

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.2906529 ◽

1991 ◽

Vol 113 (1) ◽

pp. 40-50 ◽

Cited By ~ 1

Author(s):

R. H. Tindell

Keyword(s):

System Integration ◽

Fluid Dynamic ◽

Low Cost ◽

Separated Flow ◽

Propulsion System ◽

Navier Stokes ◽

Aerospace Vehicles ◽

Design Engineers ◽

Flow Phenomena ◽

The Impact

The impact of computational fluid dynamics (CFD) methods on the development of advanced aerospace vehicles is growing stronger year by year. Design engineers are now becoming familiar with CFD tools and are developing productive methods and techniques for their applications. This paper presents and discusses applications of CFD methods used at Grumman to design and predict the performance of propulsion system elements such as inlets and nozzles. The paper demonstrates techniques for applying various CFD codes and shows several interesting and unique results. A novel application of a supersonic Euler analysis of an inlet approach flow field, to clarify a wind tunnel-to-flight data conflict, is presented. In another example, calculations and measurements of low-speed inlet performance at angle of attack are compared. This is highlighted by employing a simplistic and low-cost computational model. More complex inlet flow phenomena at high angles of attack, calculated using an approach that combines a panel method with a Navier-Stokes (N-S) code, is also reviewed. The inlet fluid mechanics picture is rounded out by describing an N-S calculation and a comparison with test data of an offset diffuser having massively separated flow on one wall. Finally, the propulsion integration picture is completed by a discussion of the results of nozzle-afterbody calculations, using both a complete aircraft simulation in a N-S code, and a more economical calculation using an equivalent body of revolution technique.

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Influence of Even-Order Dispersion on Super-Sech Soliton Transmission Quality under Coherent Crosstalk

Research Letters in Optics ◽

10.1155/2008/613986 ◽

2008 ◽

Vol 2008 ◽

pp. 1-5 ◽

Cited By ~ 4

Author(s):

Aleksandra Panajotovic ◽

Daniela Milovic ◽

Anjan Biswas ◽

Essaid Zerrad

Keyword(s):

Fourth Order ◽

Optical Network ◽

Single Mode ◽

Single Mode Fiber ◽

Higher Order ◽

Trailing Edges ◽

Even Order ◽

Transmission Quality ◽

The Impact ◽

Order Dispersion

The transmission speed of optical network strongly depends on the impact of higher order dispersion. In presence of coherent crosstalk, which cannot be otherwise controlled by optical filtering, the impact of higher order dispersions becomes more pronounced. In this paper, the general expressions, that describe pulse deformation due to second- and fourth-order dispersions in a single-mode fiber, are given. The responses for such even-order dispersions, in presence of coherent crosstalk, are characterized by waveforms with long trailing edges. The transmission quality of optical pulses, due to both individual and combined influence of second- and fourth-order dispersions, is studied in this paper. Finally, the pulse shape and eye diagrams are obtained.

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Experimental investigation of isothermal and reacting flow characteristics downstream of axisymmetric bluff body stabilizers under stratified or fully premixed inlet mixture conditions

10.12681/eadd/48856 ◽

2020 ◽

Author(s):

Γεώργιος Πατεράκης

Keyword(s):

Experimental Investigation ◽

Turbulent Flow ◽

Bluff Body ◽

Operating Conditions ◽

Reacting Flow ◽

Wide Range ◽

Flow Features ◽

Air Mixing ◽

The Impact ◽

Stratified Flames

The current work describes an experimental investigation of isothermal and turbulent reacting flow field characteristics downstream of axisymmetric bluff body stabilizers under a variety of inlet mixture conditions. Fully premixed and stratified flames established downstream of this double cavity premixer/burner configuration were measured and assessed under lean and ultra-lean operating conditions. The aim of this thesis was to further comprehend the impact of stratifying the inlet fuelair mixture on the reacting wake characteristics for a range of practical stabilizers under a variety of inlet fuel-air settings. In the first part of this thesis, the isothermal mean and turbulent flow features downstream of a variety of axisymmetric baffles was initially examined. The effect of different shapes, (cone or disk), blockage ratios, (0.23 and 0.48), and rim thicknesses of these baffles was assessed. The variations of the recirculation zones, back flow velocity magnitude, annular jet ejection angles, wake development, entrainment efficiency, as well as several turbulent flow features were obtained, evaluated and appraised. Next, a comparative examination of the counterpart turbulent cold fuel-air mixing performance and characteristics of stratified against fully-premixed operation was performed for a wide range of baffle geometries and inlet mixture conditions. Scalar mixing and entrainment properties were investigated at the exit plane, at the bluff body annular shear layer, at the reattachment region and along the developing wake were investigated. These isothermal studies provided the necessary background information for clarifying the combustion properties and interpreting the trends in the counterpart turbulent reacting fields. Subsequently, for selected bluff bodies, flame structures and behavior for operation with a variety of reacting conditions were demonstrated. The effect of inlet fuel-air mixture settings, fuel type and bluff body geometry on wake development, flame shape, anchoring and structure, temperatures and combustion efficiencies, over lean and close to blow-off conditions, was presented and analyzed. For the obtained measurements infrared radiation, particle image velocimetry, laser doppler velocimetry, chemiluminescence imaging set-ups, together with Fouriertransform infrared spectroscopy, thermocouples and global emission analyzer instrumentation was employed. This helped to delineate a number of factors that affectcold flow fuel-air mixing, flame anchoring topologies, wake structure development and overall burner performance. The presented data will also significantly assist the validation of computational methodologies for combusting flows and the development of turbulence-chemistry interaction models.

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Suggestions to the test procedure for technical means of protection of steel welded domestic LPG gas cylinders from physical destruction in fire

Pozharnaia bezopasnost` ◽

10.37657/vniipo.pb.2021.87.79.008 ◽

2021 ◽

pp. 67-72

Author(s):

Владимир Леонидович Малкин ◽

Владимир Александрович Угорелов ◽

Петр Алексеевич Леончук ◽

Руслан Андреевич Загуменников

Keyword(s):

Coming Out ◽

Test Procedure ◽

Video Recording ◽

Heating System ◽

Measuring System ◽

Cylinder Surface ◽

In Fire ◽

Gas Leaks ◽

The Impact ◽

Gas Cylinders

Разработана методика проведения испытаний технических средств защиты стальных сварных бытовых баллонов для сжиженных углеводородных газов (СУГ) от физического разрушения при воздействии на них пожара. В методике содержатся требования к отбору газовых баллонов, рассматриваемым модельным сценариям, установке для испытаний, мероприятиям по подготовке испытаний, порядку их проведения, к отчету о проведении испытаний. Использование предлагаемой методики позволит с высокой степенью достоверности оценивать эффективность применения технических средств защиты стальных бытовых баллонов для СУГ от физического разрушения при воздействии пожара. The paper contains proposals for inclusion in the testing methodology for technical means of protecting gas cylinders from physical destruction. The proposals relate to the choice of typical scenarios characteristic for emergencies and fire development in a room with LPG cylinders: the ingress of cylinders into the fire center, the impact on the cylinder surface of the heat flow of the adjacent fire center; the impact on the surface of the cylinder of LPG vapors jet combustion, simulating the effect of combustion of LPG vapors coming out of the outlet of the valve (safety valve or membrane) of the adjacent cylinder. The design of the installation for testing cylinders in accordance with the above scenarios is presented. There are given requirements for the test preparation procedure, including the verification of documentation, installation of technical protective equipment, filling and delivery of cylinders, checking for gas leaks from cylinders after delivery, installation for testing. A detailed description of the installation procedure is given in accordance with the presented diagrams for various test scenarios. The basic diagrams of the measuring system for the pressure inside the cylinder, mounting of thermocouples on the wall of the cylinder, and remote supply of liquid fuel to trays are described. There is described the test procedure, which consists of turning on the recording systems, gas supplying to the installation, activating the cylinder heating system, video recording of the experiment with timing, closing the valve in front of the pressure sensor after the end of combustion, discharging LPG from the sealed cylinder to the burner. The requirements for the composition of the test report are given, which make it possible to confirm the reliability of the experiments.

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On turbulent separation in the flow past a bluff body

Journal of Fluid Mechanics ◽

10.1017/s0022112092002118 ◽

1992 ◽

Vol 241 ◽

pp. 443-467 ◽

Cited By ~ 24

Author(s):

A. Neish ◽

F. T. Smith

Keyword(s):

Large Scale ◽

Bluff Body ◽

Separated Flow ◽

Small Scale ◽

Supporting Evidence ◽

Turbulent Regime ◽

Trailing Edge ◽

Flow Past ◽

Starting Point ◽

Turbulence Factor

The basic model problem of separation as predicted by the time-mean boundary-layer equations is studied, with the Cebeci-Smith model for turbulent stresses. The changes between laminar and turbulent flow are investigated by means of a turbulence ‘factor’ which increases from zero for laminar flow to unity for the fully turbulent regime. With an attached-flow starting point, a small increase in the turbulence factor above zero is found to drive the separation singularity towards the trailing edge or rear stagnation point for flow past a circular cylinder, according to both computations and analysis. A separated-flow starting point is found to produce analogous behaviour for the separation point. These findings lead to the suggestion that large-scale separation need not occur at all in the fully turbulent regime at sufficiently high Reynolds number; instead, separation is of small scale, confined near the trailing edge. Comments on the generality of this suggestion are presented, along with some supporting evidence from other computations. Further, the small scale involved theoretically has values which seem reasonable in practical terms.

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