Crossflow Instability Analysis for Swept Laminar Flow Wings Using Crossflow Pressure Gradient

AIAA Journal ◽  
2021 ◽  
pp. 1-12
Author(s):  
Zhen-Ming Xu ◽  
Zhong-Hua Han ◽  
Jiang-Bo Chi ◽  
Zhu Zhen ◽  
Wen-Ping Song
Keyword(s):  
Laminar Flow ◽  
Pressure Gradient ◽  
Instability Analysis ◽  
Crossflow Instability

Time-Dependent Laminar Flow in Curved Channels

1970 ◽  
Vol 37 (3) ◽  
pp. 838-843 ◽  
Author(s):  
R. J. Nunge
Keyword(s):  
Laminar Flow ◽  
Pressure Gradient ◽  
Constant Pressure ◽  
Time Dependent ◽  
Pressure Gradients ◽  
Straight Channel ◽  
Curvature Ratio ◽  
Curved Channels ◽  
Developing Flow ◽  
Time Required

The velocity distribution for time-dependent laminar flow in curved channels is derived. The analysis applies to flows with pressure gradients which are arbitrary functions of time. Numerical results are obtained for developing flow due to a constant pressure gradient. Developing flow in a straight channel is also discussed and it is found that the curvature ratio has only a small effect on the time required to reach the fully developed state.

Transient Boundary Layers Between Porous Plates

1976 ◽  
Vol 43 (4) ◽  
pp. 555-558 ◽  
Author(s):  
W. A. Fiveland ◽  
P.-C. Lu
Keyword(s):  
Laminar Flow ◽  
Pressure Gradient ◽  
Incompressible Fluid ◽  
Boundary Layers ◽  
Parallel Plate ◽  
Flow Patterns ◽  
Numerical Results ◽  
Sine Transform ◽  
Fourier Sine Transform ◽  
Plate Channel

Analysis is made of a transient, fully developed, laminar flow of an incompressible fluid in a porous, parallel-plate channel. The crossflow through the plates is uniform, but is allowed to vary with time. In addition to a pressure gradient due to pumping, the flow is also under the inducement of the motion of one of the plates. Numerical results are obtained through the (final or nonfinal) use of the finite Fourier sine transform. Asymptotic flow patterns showing transient boundary layers are investigated. Finally, the formation of the flow from the start is described in physical terms.

Effect of Rotation on Laminar Compressible Fluid Flow in a Vertical Cylinder

1972 ◽  
Vol 94 (2) ◽  
pp. 506-508
Author(s):  
E. J. Hahn
Keyword(s):  
Fluid Flow ◽  
Laminar Flow ◽  
Pressure Gradient ◽  
Incompressible Flow ◽  
Compressible Fluid ◽  
Vertical Cylinder ◽  
Operating Conditions ◽  
Friction Loss ◽  
Compressible Fluid Flow ◽  
Compressibility Effects

Solutions are obtained for fully developed laminar flow of a compressible fluid through a rotating vertical cylinder. The results enable the velocity, friction loss, and pressure gradient to be easily calculated from corresponding incompressible flow solutions. It is shown that compressibility effects may be neglected completely over a practical range of operating conditions, such as encountered in centrifugal aerosol separators, enabling the flow analyses in these more complicated configurations to be justifiably simplified.

Bounds on Two-Phase Frictional Pressure Gradient in Minichannels and Microchannels

2006 ◽  
Author(s):  
M. M. Awad ◽  
Y. S. Muzychka
Keyword(s):  
Laminar Flow ◽  
Pressure Gradient ◽  
Flow Model ◽  
Narrow Channel ◽  
Published Data ◽  
Phase Flow ◽  
Water Mixture ◽  
Two Phase ◽  
Working Fluids ◽  
Simple Rules

Simple rules are developed for obtaining rational bounds for two-phase frictional pressure gradient in minichannels and microchannels. The lower bound is based on Ali et al. correlation for laminar-laminar flow. This correlation is based on modification of simplified stratified flow model derived from the theoretical approach of Taitel and Dukler for the case of two-phase flow in a narrow channel. The upper bound is based on Chisholm correlation for laminar-laminar flow. The model is verified using published experimental data of two-phase frictional pressure gradient in circular and non-circular shapes. The published data include different working fluids such as air-water mixture and nitrogen-water mixture, and different channel diameters. The bounds models are also presented in a dimensionless form as two-phase frictional multiplier (φl and φg) versus Lockhart-Martinelli parameter (X) for different working fluids such as air-water mixture and nitrogen-water mixture. It is shown that the published data can be well bounded.

Experiments on the Laminar Flow in a Rectangular Streamwise Corner

1978 ◽  
Vol 29 (2) ◽  
pp. 75-97 ◽  
Author(s):  
H.A. El-Gamal ◽  
W.H. Barclay
Keyword(s):  
Laminar Flow ◽  
Pressure Gradient ◽  
Experimental Work ◽  
Marked Effect ◽  
Leading Edge ◽  
Experimental Results ◽  
Edge Geometry ◽  
Significant Difference ◽  
Streamwise Pressure Gradient ◽  
Corner Layer

SummaryThe results of measurements in the flow along a rectangular corner are presented in the form of velocity profiles. The profiles form two sets: one for flow in a slightly favourable streamwise pressure gradient and one for flow when the pressure gradient is ‘practically zero’. The appearance of the profiles is quite different from that of previously reported experimental work and it is suggested here that the primary cause of this is the different type of corner leading edges used in each case. The flow appears to be only marginally stable and even very slightly changed entry conditions caused by alterations in the leading edge geometry may have a marked effect on the profiles further downstream. The new results are consistent with the notion of corner layer similarity (an implication in every attempted theoretical solution) but there remains a significant difference between the experimental results and the more reliable theoretical solutions available.

An Explicit and Continuously Differentiable Flow Equation for Non-Newtonian Fluids in Pipes

SPE Journal ◽  
2013 ◽  
Vol 19 (01) ◽  
pp. 78-87
Author(s):  
Kristian Gjerstad ◽  
B. Erik Ydstie ◽  
Rune W. Time ◽  
Knut S. Bjørkevoll
Keyword(s):  
Simple Model ◽  
Laminar Flow ◽  
Pressure Gradient ◽  
Real Time ◽  
Flow Equation ◽  
Newtonian Fluids ◽  
Numerical Implementation ◽  
Time Optimization ◽  
Drilling Operations ◽  
Real Time Optimization

Summary A simple model approximates Herschel-Bulkley (HB) non-Newtonian fluids in laminar flow in pipes. It is continuously differentiable and explicit in the frictional pressure gradient. Such properties are needed for control, real-time optimization, and prediction in drilling operations. The accuracy of the new model is evaluated by comparing it with a numerical implementation of the implicit HB model and some representative approximations used in the literature. Very little loss in accuracy is experienced compared with the implicit solution.

Relaminarization in highly accelerated turbulent boundary layers

1973 ◽  
Vol 61 (3) ◽  
pp. 417-447 ◽  
Author(s):  
R. Narasimha ◽  
K. R. Sreenivasan
Keyword(s):  
Boundary Layer ◽  
Laminar Flow ◽  
Pressure Gradient ◽  
Laminar Boundary Layer ◽  
Outer Layer ◽  
Transitional Region ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Turbulence Decay ◽  
The Mean

The mean flow development in an initially turbulent boundary layer subjected to a large favourable pressure gradient beginning at a point x0 is examined through analyses expected a priori to be valid on either side of relaminarization. The ‘quasi-laminar’ flow in the later stages of reversion, where the Reynolds stresses have by definition no significant effect on the mean flow, is described by an asymptotic theory constructed for large values of a pressure-gradient parameter Λ, scaled on a characteristic Reynolds stress gradient. The limiting flow consists of an inner laminar boundary layer and a matching inviscid (but rotational) outer layer. There is consequently no entrainment to lowest order in Λ−1, and the boundary layer thins down to conserve outer vorticity. In fact, the predictions of the theory for the common measures of boundary-layer thickness are in excellent agreement with experimental results, almost all the way from x0. On the other hand the development of wall parameters like the skin friction suggests the presence of a short bubble-shaped reverse-transitional region on the wall, where neither turbulent nor quasi-laminar calculations are valid. The random velocity fluctuations inherited from the original turbulence decay with distance, in the inner layer, according to inverse-power laws characteristic of quasi-steady perturbations on a laminar flow. In the outer layer, there is evidence that the dominant physical mechanism is a rapid distortion of the turbulence, with viscous and inertia forces playing a secondary role. All the observations available suggest that final retransition to turbulence quickly follows the onset of instability in the inner layer.It is concluded that reversion in highly accelerated flows is essentially due to domination of pressure forces over the slowly responding Reynolds stresses in an originally turbulent flow, accompanied by the generation of a new laminar boundary layer stabilized by the favourable pressure gradient.

Modeling of a MEMS Floating Element Shear Sensor

2014 ◽  
Vol 1659 ◽  
pp. 35-42
Author(s):  
Nikolas Kastor ◽  
Zhengxin Zhao ◽  
Robert D. White
Keyword(s):  
Shear Stress ◽  
Laminar Flow ◽  
Pressure Gradient ◽  
Flow Direction ◽  
Flow Cell ◽  
Surface Shear Stress ◽  
Cfd Model ◽  
Shear Sensor ◽  
Floating Element ◽  
Gradient Effects

ABSTRACTA MEMS floating element shear stress sensor has been developed for flow testing applications, targeted primarily in ground and flight testing of aerospace vehicle and components. However, concerns remain about the interaction of the flow with the mechanical elements of the structure at the micro-scale. In particular, there are concerns about the validity of laminar flow cell calibration to measurement in turbulent flows, and the extent to which pressure gradients may introduce errors into the shear stress measurement. In order to address these concerns, a numerical model of the sensor has been constructed.In this paper, a computational fluid dynamics (CFD) model is described. The CFD model directly models a laminar flow cell experiment that is used to calibrate the shear sensor. The computational model allows us to quantify the contributions (e.g. pressure gradient vs. shear, top surface vs. lateral surfaces) to the sensor output in a manner that is difficult by purely experimental means. The results are compared to experimental data, validating the model and resulting in the following: Surface shear stress contributes approximately 40% of the total flow direction force; pressure gradient effects contribute nearly 45% for the textured shuttle described here; lift forces and pitching moments are non-zero. Thus, it is found that flow interactions are complex and that it is insufficient to simply assume that flow forces on the sensor are the top area multiplied by wall shear, as is sometimes done. Pressure gradient effects, at least, must be included for accurate calibration.

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