Drag Reduction of a Cylinder/Endwall Junction Using the Iceformation Method

1993 ◽  
Vol 115 (1) ◽  
pp. 26-32 ◽  
Author(s):  
R. S. LaFleur ◽  
L. S. Langston
Keyword(s):  
Boundary Layer ◽  
Design Method ◽  
Three Dimensional ◽  
Control Parameters ◽  
Cylinder Wake ◽  
Adaptive Selection ◽  
Vortex Model ◽  
Optimal Contour ◽  
Flow Visualizations ◽  
High Reynolds

The iceformation design method was used to reduce the drag of a juncture between a cylinder and flat endwall. Ice was formed on a subfreezing flat endwall in a warmer laminar water flow. The ice shape was influenced by and altered the three-dimensional separated boundary layer and the cylinder wake. Preliminary experiments were used to indicate control parameter relationships. An adaptive selection theory was used to determine optimal control parameters. A sample optimal contour was generated and tested for juncture drag performance. High Reynolds number wind tunnel drag tests showed that the iceform contour had an average of 18 percent lower drag than a flat plate juncture given the same upstream boundary layer conditions. Flow visualizations showed that the iceform contour produced three larger diameter vortices compared to the laminar four vortex model of Baker (1979).

On the nonlinear evolution of a pair of oblique Tollmien–Schlichting waves in boundary layers

1997 ◽  
Vol 340 ◽  
pp. 361-394 ◽  
Author(s):  
XUESONG WU ◽  
S. J. LEIB ◽  
M. E. GOLDSTEIN
Keyword(s):  
Boundary Layer ◽  
Phase Angle ◽  
Spatial Scales ◽  
Asymptotic Methods ◽  
Three Dimensional ◽  
Critical Layer ◽  
Back Reaction ◽  
Finite Distance ◽  
Tollmien Schlichting ◽  
High Reynolds

This paper is concerned with the nonlinear interaction and development of a pair of oblique Tollmien–Schlichting waves which travel with equal but opposite angles to the free stream in a boundary layer. Our approach is based on high-Reynolds-number asymptotic methods. The so-called ‘upper-branch’ scaling is adopted so that there exists a well-defined critical layer, i.e. a thin region surrounding the level at which the basic flow velocity equals the phase velocity of the waves. We show that following the initial linear growth, the disturbance evolves through several distinct nonlinear stages. In the first of these, nonlinearity only affects the phase angle of the amplitude of the disturbance, causing rapid wavelength shortening, while the modulus of the amplitude still grows exponentially as in the linear regime. The second stage starts when the wavelength shortening produces a back reaction on the development of the modulus. The phase angle and the modulus then evolve on different spatial scales, and are governed by two coupled nonlinear equations. The solution to these equations develops a singularity at a finite distance downstream. As a result, the disturbance enters the third stage in which it evolves over a faster spatial scale, and the critical layer becomes both non-equilibrium and viscous in nature, in contrast to the two previous stages, where the critical layer is in equilibrium and purely viscosity dominated. In this stage, the development is governed by an amplitude equation with the same nonlinear term as that derived by Wu, Lee & Cowley (1993) for the interaction between a pair of Rayleigh waves. The solution develops a new singularity, leading to the fourth stage where the flow is governed by the fully nonlinear three-dimensional inviscid triple-deck equations. It is suggested that the stages of evolution revealed here may characterize the so-called ‘oblique breakdown’ in a boundary layer. A discussion of the extension of the analysis to include the resonant-triad interaction is given.

A nonlinear, asymptotic investigation of the stationary modes of instability of the three-dimensional boundary layer on a rotating disc

1987 ◽  
Vol 413 (1845) ◽  
pp. 497-513 ◽  
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Nonlinear Effects ◽  
Finite Amplitude ◽  
Neutral Stability ◽  
Lower Branch ◽  
Rotating Disc ◽  
Dimensional Boundary ◽  
High Reynolds ◽  
Set Up

There exist two types of stationary instability of the flow over a rotating disc corresponding to the upper, inviscid mode and the lower-branch mode, which has a triple-deck structure, of the neutral stability curve. The linear problem has been investigated by P. Hall ( Proc. R. Soc. Lond. A 406, 93-106 (1986)) and the asymptotic structure of the wavenumber and orientation of these modes has been obtained. Here, a nonlinear investigation of high Reynolds number, stationary instabilities in the three-dimensional boundary layer on a rotating disc is given for the lower branch mode. By considering nonlinear effects and following the framework set up by Hall, asymptotic solutions are obtained that enable the finite amplitude growth of a disturbance close to the neutral location to be described.

The effect of aspect ratio on the wake structure of finite wall-mounted square cylinders

2019 ◽  
Vol 875 ◽  
pp. 929-960 ◽  
Author(s):  
Yendrew Yauwenas ◽  
Ric Porteous ◽  
Danielle J. Moreau ◽  
Con J. Doolan
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
Amplitude Modulation ◽  
Dimensional Space ◽  
Three Dimensional ◽  
Cylinder Wake ◽  
Near Wake ◽  
Wake Structure ◽  
Velocity Amplitude ◽  
Aspect Ratios

This paper presents a combined experimental and large-eddy simulation study to characterise the effect of aspect ratio on the near-wake structure of a square finite wall-mounted cylinder (FWMC). The cylinder aspect ratios (span $L$ to width $W$) investigated in the experiments were $1.4\leqslant L/W\leqslant 21.4$ and the oncoming boundary-layer thicknesses were $1.3W$ and $0.9W$ at a Reynolds number based on cylinder width of $1.4\times 10^{4}$ and $1.1\times 10^{4}$, respectively. In complementary simulations, the cylinder aspect ratios investigated were 1.4, 4.3, 10 and 18.6. The cylinder wake structure was visualised in three-dimensional space using a vortex core detection method and decomposed to its oscillation modes using the spectral proper orthogonal decomposition (SPOD) technique. A parametric diagram is proposed to predict whether the time-averaged wake structure is a dipole or a quadrupole pattern, based on oncoming boundary-layer height and aspect ratio. Cellular shedding occurs when the aspect ratio is high with up to three shedding cells occurring across the span for aspect ratios $L/W>18$. Each of these cells sheds at a distinct frequency, as evidenced by the spectral content of the surface pressure measured on the side face and the near-wake velocity. Amplitude modulation is also observed in the vortex shedding, which explains the amplitude modulation of the acoustic pressure emitted by square FWMCs. SPOD is shown to be a viable method to identify the occurrence of cellular shedding in the wake.

Steady motion through a branching tube

1977 ◽  
Vol 355 (1681) ◽  
pp. 167-187 ◽  
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Cross Sections ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Steady Motion ◽  
Nonlinear Behaviour ◽  
Initial Development ◽  
Secondary Motion ◽  
High Reynolds

The fluid motion through a straight pipe that bifurcates symmetrically into two semi-circular pipes is considered at high Reynolds numbers, with the aim of deriving some of the effects of the three-dimensionality per se. In a corresponding planar problem the long-scale boundary layer approach yields the initial development of the induced pressure gradient fairly directly, the problem being linear. By contrast, in the three-dimensional situation the favourable pressure gradient is determined by a nonlinear eigenvalue relation, because the pressure gradient is much stronger here and interacts critically with the inviscid coreflow to produce nonlinear behaviour near the outer walls. The proposed structure of the initial part of the boundary layer is apparently self-consistent, with a two-tiered development near the outer walls where the secondary motion is of a relatively fast vortex type and the axial skin friction suffers a sharp increase. The secondary coreflow is a displacement-induced streaming combined with a vortex provoked by the pressure gradient. The analysis applies for any realistic oncoming flow in the single tube and can be extended to treat other tube cross-sections.

Experimental and Numerical Study of a Subsonic Aspirated Cascade

2012 ◽  
Author(s):  
Antoine Godard ◽  
François Bario ◽  
Stéphane Burguburu ◽  
Francis Lebœuf
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Numerical Study ◽  
Design Method ◽  
Active Flow Control ◽  
Three Dimensional ◽  
Design Feature ◽  
Suction Side ◽  
Compressor Blades ◽  
Pressure Losses

This paper presents the validation of a design method for aspirated compressor blades, combining a passive separation control by blade shaping with an active flow control by aspiration. In a first part, a linear aspirated cascade designed according to this method was built and tested at low speed, without and with aspiration. The latter was only applied on the suction surfaces of the blades. Particle Image Velocimetry measurements performed at mid-span of the cascade, in the central passage, showed a complete reattachment of the separated boundary layer on the suction side of the blade. A flow deflection of approximately 65 degrees was achieved requiring an aspirated mass flow rate of 3.3%. However, boundary layer reattachment is effective in a zone centered at mid-span covering 30% of blade span. Flow visualization revealed large corner separation in the presence of aspiration. This is due to the re-establishment of strong pressure gradient on sidewalls of the cascade. No flow control was applied on these zones for optical access purpose. These secondary-flow regions reduced the diffusion occurring within the cascade by nearly 60% in comparison with the design intent. They also increased the expected level of total pressure losses measured by wake traverses downstream of the cascade. In a second part, numerical simulations of the aforementioned experiment were carried out to help the understanding of the experimental results. The simulations were able to reproduce correctly the characteristic flow features, without and with aspiration, observed and measured during the experiment. Thus, they confirmed the potential of this design method developed for aspirated compressor blades, as well as CFD capabilities to simulate the influence of technological effects like suction slots. A uniform and a non-uniform aspiration distribution along the blade span direction were considered during simulations. Suction distribution was found to have a significant impact on the control by aspiration. This design feature, in addition to flow control on endwalls, has to be taken into account in the three-dimensional design of highly loaded aspirated compressor blades.

scholarly journals Spillage-Adaptive Fixed-Geometry Bump Inlet of Wide Speed Range

Aerospace ◽  
2021 ◽  
Vol 8 (11) ◽  
pp. 340
Author(s):  
Zonghan Yu ◽  
Guoping Huang ◽  
Ruilin Wang ◽  
Omer Musa
Keyword(s):  
Boundary Layer ◽  
Design Method ◽  
Three Dimensional ◽  
Low Speed ◽  
Flight Vehicles ◽  
Integration Pattern ◽  
Speed Range ◽  
Flexible Integration ◽  
Wide Speed Range ◽  
Future Work

In this work, a new spillage-adaptive bump inlet concept is proposed to widen the speed range for hypersonic air-breathing flight vehicles. Various approaches to improve the inlet start-ability are summarized and compared, among which the bump-inlet pattern holds the merits of high lift-to-drag ratio, boundary layer diversion, and flexible integration ability. The proposed spillage-adaptive concept ensures the inlet starting performance by spilling extra mass flow away at low speed number conditions. The inlet presetting position is determined by synthetically evaluating the flow uniformity and the low-kinetic-energy fluid proportion. The numerical results show that the flow spillage of the inlet increases with the inflow speed decrease, which makes the inlet easier to start at low speed conditions (M 2.5–6.0). The effects of the boundary layer on spillage are also studied in this work. The new integration pattern releases the flow spillage potentials of three-dimensional inward-turning inlets by reasonably arranging the inlet compression on the bump surface. Future work will focus on the spillage-controllable design method.

The interacting boundary-layer flow due to a vortex approaching a cylinder

1997 ◽  
Vol 346 ◽  
pp. 319-343 ◽  
Author(s):  
Z. XIAO ◽  
O. R. BURGGRAF ◽  
A. T. CONLISK
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Boundary Layer Separation ◽  
Two Dimensions ◽  
Unsteady Boundary Layer ◽  
Reynolds Number Flow ◽  
Boundary Layer Equations ◽  
Number Flow ◽  
Layer Flow ◽  
High Reynolds

In this paper the solution to the three-dimensional and unsteady interacting boundary-layer equations for a vortex approaching a cylinder is calculated. The flow is three-dimensional and unsteady. The purpose of this paper is to enhance the understanding of the structure in three-dimensional unsteady boundary-layer separation commonly observed in a high-Reynolds-number flow. The short length scales associated with the boundary-layer eruption process are resolved through an efficient and effective moving adaptive grid procedure. The results of this work suggest that like its two-dimensional counterpart, the three-dimensional unsteady interacting boundary layer also terminates in a singularity at a finite time. Furthermore, the numerical calculations confirm the theoretical analysis of the singular structure in two dimensions for the interacting boundary layer due to Smith (1988).

On the inviscid instability of certain two-dimensional vortex-type flows

1967 ◽  
Vol 29 (4) ◽  
pp. 647-666 ◽  
Author(s):  
Alfons Michalke ◽  
Adalbert Timme
Keyword(s):  
Boundary Layer ◽  
Free Boundary ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Rotating Fluids ◽  
Single Vortex ◽  
Vortex Model ◽  
Breakdown Phenomenon ◽  
Extremum Value ◽  
Inviscid Instability

As a contribution to the breakdown phenomenon of vortices in a two-dimensional free boundary layer, this paper deals with the question whether a single cylindrical (i.e. two-dimensional) vortex can become unstable. For this reason a single vortex, as it occurs in a free boundary layer, is approximated by an axisymmetrical vortex model. The inviscid stability theory of rotating fluids is then applied to this vortex model. By general stability criteria it was found that a vortex consisting of vorticity of one sign only is stable according to the Rayleigh criterion, but, if the vorticity has an extremum value outside the axis, may become unstable with respect to cylindrical disturbances. Furthermore, stability calculations for three special types of vortex were performed. It was found that they were more unstable with respect to cylindrical disturbances than to three-dimensional ones.

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