The effect of wall temperature distribution on streaks in compressible turbulent boundary layer

2018 ◽  
Vol 32 (12n13) ◽  
pp. 1840051
Author(s):  
Zhao Zhang ◽  
Yang Tao ◽  
Neng Xiong ◽  
Fengxue Qian
Keyword(s):  
Boundary Layer ◽  
Temperature Distribution ◽  
Turbulent Boundary Layer ◽  
Wall Temperature ◽  
Friction Velocity ◽  
Energy Equation ◽  
Wall Region ◽  
The Mean ◽  
Isothermal Wall ◽  
Adiabatic Case

The thermal boundary condition at wall is very important for the compressible flow due to the coupling of the energy equation, and a lot of research works about it were carried out in past decades. In most of these works, the wall was assumed as adiabatic or uniform isothermal surface; the flow over a thermal wall with some special temperature distribution was seldom studied. Lagha studied the effect of uniform isothermal wall on the streaks, and pointed out that higher the wall temperature is, the longer the streak (POF, 2011, 23, 015106). So, we designed streamwise stripes of wall temperature distribution on the compressible turbulent boundary layer at Mach 3.0 to learn the effect on the streaks by means of direct numerical simulation in this paper. The mean wall temperature is equal to the adiabatic case approximately, and the width of the temperature stripes is in the same order as the width of the streaks. The streak patterns in near-wall region with different temperature stripes are shown in the paper. Moreover, we find that there is a reduction of friction velocity with the wall temperature stripes when compared with the adiabatic case.

The Effects of Surface Roughness on the Mean Velocity Profile in a Turbulent Boundary Layer

2002 ◽  
Vol 124 (3) ◽  
pp. 664-670 ◽  
Author(s):  
Donald J. Bergstrom ◽  
Nathan A. Kotey ◽  
Mark F. Tachie
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Turbulent Boundary Layer ◽  
Velocity Profile ◽  
Friction Velocity ◽  
Outer Region ◽  
Stream Velocity ◽  
Mean Velocity ◽  
Outer Flow ◽  
The Mean

Experimental measurements of the mean velocity profile in a canonical turbulent boundary layer are obtained for four different surface roughness conditions, as well as a smooth wall, at moderate Reynolds numbers in a wind tunnel. The mean streamwise velocity component is fitted to a correlation which allows both the strength of the wake, Π, and friction velocity, Uτ, to vary. The results show that the type of surface roughness affects the mean defect profile in the outer region of the turbulent boundary layer, as well as determining the value of the skin friction. The defect profiles normalized by the friction velocity were approximately independent of Reynolds number, while those normalized using the free stream velocity were not. The fact that the outer flow is significantly affected by the specific roughness characteristics at the wall implies that rough wall boundary layers are more complex than the wall similarity hypothesis would allow.

scholarly journals The rough favourable pressure gradient turbulent boundary layer

2009 ◽  
Vol 641 ◽  
pp. 129-155 ◽  
Author(s):  
RAÚL BAYOÁN CAL ◽  
BRIAN BRZEK ◽  
T. GUNNAR JOHANSSON ◽  
LUCIANO CASTILLO
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Rough Surface ◽  
Reynolds Stress ◽  
Friction Velocity ◽  
Free Stream ◽  
Stream Velocity ◽  
The Mean ◽  
Stress Profiles

Laser Doppler anemometry measurements of the mean velocity and Reynolds stresses are carried out for a rough-surface favourable pressure gradient turbulent boundary layer. The experimental data is compared with smooth favourable pressure gradient and rough zero-pressure gradient data. The velocity and Reynolds stress profiles are normalized using various scalings such as the friction velocity and free stream velocity. In the velocity profiles, the effects of roughness are removed when using the friction velocity. The effects of pressure gradient are not absorbed. When using the free stream velocity, the scaling is more effective absorbing the pressure gradient effects. However, the effects of roughness are almost removed, while the effects of pressure gradient are still observed on the outer flow, when the mean deficit velocity profiles are normalized by the U∞ δ∗/δ scaling. Furthermore, when scaled with U2∞, the 〈u2〉 component of the Reynolds stress augments due to the rough surface despite the imposed favourable pressure gradient; when using the friction velocity scaling u∗2, it is dampened. It becomes ‘flatter’ in the inner region mainly due to the rough surface, which destroys the coherent structures of the flow and promotes isotropy. Similarly, the pressure gradient imposed on the flow decreases the magnitude of the Reynolds stress profiles especially on the 〈v2〉 and -〈uv〉 components for the u∗2 or U∞2 scaling. These effects are reflected in the boundary layer parameter δ∗/δ, which increase due to roughness, but decrease due to the favourable pressure gradient. Additionally, the pressure parameter Λ found not to be in equilibrium, describes the development of the turbulent boundary layer, with no influence of the roughness linked to this parameter. These measurements are the first with an extensive number of downstream locations (11). This makes it possible to compute the required x-dependence for the production term and the wall shear stress from the full integrated boundary layer equation. The finding indicates that the skin friction coefficient depends on the favourable pressure gradient condition and surface roughness.

On The Nature of Jets Entering A Turbulent Flow: Part A—Jet–Mainstream Interaction

1979 ◽  
Vol 101 (3) ◽  
pp. 459-465 ◽  
Author(s):  
K. Kadotani ◽  
R. J. Goldstein
Keyword(s):  
Boundary Layer ◽  
Temperature Distribution ◽  
Turbulent Boundary Layer ◽  
Turbulent Flow ◽  
Turbulence Intensity ◽  
Vortex Motion ◽  
Instantaneous Velocity ◽  
Turbulence Scale ◽  
Flow Part ◽  
The Mean

The effects of mainstream turbulence intensity between 0.3 percent and 20.6 percent and turbulence scale between 0.06 and 0.33 jet entrance diameters on heated and unheated subsonic jets issuing from a row of inclined round holes into a turbulent boundary layer are reported. Time averaged and instantaneous velocities and the mean temperature are measured in the flow. The mainstream turbulence scale has a significant effect on the temperature distribution of the injected jets and on the instantaneous velocity profiles of the flow following injection. When the mainstream turbulence scale is large, the injected jets are well mixed with the mainstream; when the scale is small, the injected jets are well preserved and the effect of vortex motion upon the temperature distribution becomes significant.

A turbulent boundary layer disturbed by a cylinder

1978 ◽  
Vol 87 (1) ◽  
pp. 121-141 ◽  
Author(s):  
Eisuke Marumo ◽  
Kenjiro Suzuki ◽  
Takashi Sato
Keyword(s):  
Boundary Layer ◽  
Velocity Field ◽  
Turbulent Boundary Layer ◽  
Flow Direction ◽  
Outer Region ◽  
Wall Region ◽  
Mean Velocity ◽  
Turbulent Length Scale ◽  
Axis Parallel ◽  
The Mean

This paper deals with a two-dimensional turbulent boundary layer disturbed by a circular cylinder. The cylinder was placed inside or outside the boundary layer with its axis parallel to the wall and normal to the flow direction. The mean velocity, wall shear stress, longitudinal turbulent intensity, autocorrelations and turbulent length scale were measured and here the relaxation features of the disturbed boundary layer are discussed. The measurements were made for a ratio of the cylinder diameter d to the undisturbed boundary-layer thickness δ0 equal to 0·30 and for three values of the ratio of the height h of the cylinder axis to δ0 equal to 0·222, 0·556 and 1·24.The results show that the near-wall region of the disturbed boundary layer recovers much more quickly than the outer region and that in the case h/δ0 = 0·222 the recovery is faster than in other cases, as reported by Clauser (1956). Moreover, it is found that the fluctuating velocity field recovers more slowly than the mean velocity field, and that the characteristics of the turbulence in the outer region are still close to those in the wake of an isolated cylinder at the last measurement station, although the mean velocity profile has almost completely returned to its natural shape.

Measurement of the lift force on a particle fixed to the wall in the viscous sublayer of a fully developed turbulent boundary layer

1996 ◽  
Vol 316 ◽  
pp. 285-306 ◽  
Author(s):  
A. M. Mollinger ◽  
F. T. M. Nieuwstadt
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Lift Force ◽  
Friction Velocity ◽  
Detection System ◽  
Viscous Sublayer ◽  
Average Value ◽  
The Mean ◽  
Focus Detection ◽  
The Relationship

We have investigated the lift force on a small isolated particle which is attached to a flat smooth surface and embedded within the viscous sublayer of the turbulent boundary layer over this surface. We have developed a novel experimental technique with which it is possible to measure both the mean and fluctuating lift force by gluing the particle on top of a silicium cantilever. The deflection of this cantilever is measured with a focused laser beam. The sensitivity of the focus detection system allows us to measure a lift force with an average value around 10−8N and with a standard deviation of approximately 5% of the mean. This means that our device is at least a factor of 100 more sensitive than previous devices and at the same time able to measure the lift forces on smaller particles. Data for the mean lift force (FL+) as a function of the particle radius (a+), where both parameters have been non-dimensionalized with the kinematic viscosity v and the friction velocity u*, are obtained in the range 0.3 < a+ < 2. The data support the relationship: FL+ = (56.9 ± 1.1) (a+)1.87±0.04. Also results on the fluctuating lift force have been obtained. We find that the ratio of the r.m.s. to the mean lift force is approximately 2.8.

Experimental Study on Drag-Reducing Turbulent Boundary Layer Flows of Surfactant Solutions

2007 ◽  
Author(s):  
M. Itoh ◽  
S. Tamano ◽  
T. Inoue ◽  
K. Yokota
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Drag Reduction ◽  
Laser Doppler Velocimetry ◽  
Friction Velocity ◽  
Boundary Layer Flows ◽  
Experimental Conditions ◽  
Mean Velocity ◽  
The Mean ◽  
Peak Value

In this study, the influence of a drag-reducing surfactant on the turbulent boundary layer under different solution concentrations and temperatures was extensively investigated using a two-component laser-Doppler velocimetry system. It is found that the drag reduction ratio DR at the temperature T = 20°C becomes larger downstream, and decreases with the increase of concentration from C = 65 to 150 ppm. The DR for C = 100 ppm becomes smaller with the increase of the temperature from T = 25 to 35°C, and the DR at T = 20°C is smaller than DR at T = 25°C. For the different solution concentrations and temperatures, the value of the mean velocity scaled by the friction velocity increases with increasing the amount of drag reduction. For the present experimental conditions tested, the peak value of streamwise turbulence intensity seems to be not related to the amount of DR directly and to be affected by the low Reynolds number effect strongly.

Spanwise structure in the near-wall region of a turbulent boundary layer

1990 ◽  
Vol 210 ◽  
pp. 437-458 ◽  
Author(s):  
R. A. Antonia ◽  
D. K. Bisset
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Turbulent Channel Flow ◽  
Wall Region ◽  
Level Method ◽  
The Mean ◽  
Hot Wires ◽  
Conditional Statistics ◽  
Insight Into ◽  
Near Wall

The behaviour of the stream wise velocity u in the near-wall region of a turbulent boundary layer is obtained by analysing the data from an array of hot wires aligned in the span wise direction. Conventional and conditional statistics are presented, relative to the occurrence of bursts and sweeps detected using a modified u-level method. Sweeps have an average stream wise length which is twice as large as that of bursts while the average span wise extent of sweeps is about 25% larger than that of bursts. Both instantaneous and conditionally averaged information is presented and discussed in the context of bursts and sweeps in the (x, z)-plane. Dependence on y+ is significant, and important differences are observed between instantaneous and conditionally averaged results. Conventional and conditional statistics of the velocity derivatives ∂u/∂x and ∂u/∂z provide some insight into the anisotropy of the mean-square velocity derivatives in the near-wall region. Conditionally averaged patterns of u compare favourably with the numerical simulations of Kim (1985) in the near-wall region of a turbulent channel flow, at a comparable Reynolds number.

scholarly journals Direct Numerical Simulation on Mach Number and Wall Temperature Effects in the Turbulent Flows of Flat-Plate Boundary Layer

2014 ◽  
Vol 17 (1) ◽  
pp. 189-212 ◽  
Author(s):  
Xian Liang ◽  
Xinliang Li
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Mach Number ◽  
Turbulent Boundary Layer ◽  
Direct Numerical Simulation ◽  
Flat Plate ◽  
Wall Temperature ◽  
Wall Region ◽  
Mean Velocity ◽  
Reynolds Analogy

AbstractIn this paper, direct numerical simulation (DNS) is presented for spatially evolving turbulent boundary layer over an isothermal flat-plate atMa∞= 2.25,5,6,8. WhenMa∞= 8, two cases with the ratio of wall-to-reference temperatureTω/T∞= 1.9 and 10.03 are considered respectively. The wall temperature approaches recovery temperatures for other cases. The characteristics of compressible turbulent boundary layer (CTBL) affected by freestream Mach number and wall temperature are investigated. It focuses on assessing compressibility effects and the validity of Morkovin's hypothesis through computing and analyzing the mean velocity profile, turbulent intensity, the strong Reynolds analogy (SRA) and possibility density function of dilatation term. The results show that, when the wall temperature approaches recovery temperature, the effects of Mach number on compressibility is insignificant. As a result, the compressibility effect is very weak and the Morkovin's hypothesis is still valid for Mach number even up to 8. However, when Mach number equal to 8, the wall temperature effect on the compressibility is sensitive. In this case, whenTω/T∞= 1.9, the Morkovin's hypothesis is not fully valid. The validity of classical SRA depends on wall temperature directly. A new modified SRA is proposed to eliminate such negative factor in near wall region. Finally the effects of Mach number and wall temperature on streaks are also studied.

A uniform momentum zone–vortical fissure model of the turbulent boundary layer

2018 ◽  
Vol 858 ◽  
pp. 609-633 ◽  
Author(s):  
Juan Carlos Cuevas Bautista ◽  
Alireza Ebadi ◽  
Christopher M. White ◽  
Gregory P. Chini ◽  
Joseph C. Klewicki
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Friction Velocity ◽  
Layer Structure ◽  
Turbulent Channel Flow ◽  
Streamwise Velocity ◽  
Momentum Equation ◽  
Essential Elements ◽  
The Mean

Recent studies reveal that at large friction Reynolds number $\unicode[STIX]{x1D6FF}^{+}$ the inertially dominated region of the turbulent boundary layer is composed of large-scale zones of nearly uniform momentum segregated by narrow fissures of concentrated vorticity. Experiments show that, when scaled by the boundary-layer thickness, the fissure thickness is $\mathit{O}(1/\sqrt{\unicode[STIX]{x1D6FF}^{+}})$, while the dimensional jump in streamwise velocity across each fissure scales in proportion to the friction velocity $u_{\unicode[STIX]{x1D70F}}$. A simple model that exploits these essential elements of the turbulent boundary-layer structure at large $\unicode[STIX]{x1D6FF}^{+}$ is developed. First, a master wall-normal profile of streamwise velocity is constructed by placing a discrete number of fissures across the boundary layer. The number of fissures and their wall-normal locations follow scalings informed by analysis of the mean momentum equation. The fissures are then randomly displaced in the wall-normal direction, exchanging momentum as they move, to create an instantaneous velocity profile. This process is repeated to generate ensembles of streamwise velocity profiles from which statistical moments are computed. The modelled statistical profiles are shown to agree remarkably well with those acquired from direct numerical simulations of turbulent channel flow at large $\unicode[STIX]{x1D6FF}^{+}$. In particular, the model robustly reproduces the empirically observed sub-Gaussian behaviour for the skewness and kurtosis profiles over a large range of input parameters.

The wall region of a turbulent boundary layer

1987 ◽  
Vol 30 (8) ◽  
pp. 2354 ◽  
Author(s):  
W. R. C. Phillips
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Wall Region
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