Numerical Investigations of Pressure Distribution Inside a Ventilated Supercavity

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Lei Cao ◽  
Ashish Karn ◽  
Roger E. A. Arndt ◽  
Zhengwei Wang ◽  
Jiarong Hong
Keyword(s):  
Pressure Gradient ◽  
Internal Pressure ◽  
Pressure Distribution ◽  
Numerical Study ◽  
Adverse Pressure Gradient ◽  
Air Entrainment ◽  
Gravitational Effect ◽  
Surface Model ◽  
Multiphase Model ◽  
Ventilated Supercavity

A numerical study has been conducted on the internal pressure distribution of a ventilated supercavity generated from a backward facing cavitator under different air entrainment coefficients, Froude numbers, and blockage ratios. An Eulerian multiphase model with a free surface model is employed and validated by the experiments conducted at St. Anthony Falls Laboratory of the University of Minnesota. The results show that the internal pressure in the major portion of the supercavity is primarily governed by the hydrostatic pressure of water, while a steep adverse pressure gradient occurs at the closure region. Increasing the air entrainment coefficient does not largely change the pressure distribution, while the cavity tail extends longer and consequently the pressure gradient near the closure decreases. At smaller Froude number, there is a more pronounced gravitational effect on the supercavity with increasing uplift of the lower surface of the cavity and a decreasing uniformity of the pressure distribution in the supercavity. With the increase of blockage ratio, the overall pressure within the supercavity decreases as well as the pressure gradient in the main portion of the supercavity. The current study shows that the assumption of uniform pressure distribution in ventilated supercavities is not always valid, especially at low Fr. However, an alternative definition of cavitation number in such cases remains to be defined and experimentally ascertained in future investigations.

Numerical Performance of Transition Models in Different Turbomachinery Flow Conditions: A Comparative Study

2000 ◽  
Author(s):  
Jiasen Hu ◽  
Torsten H. Fransson
Keyword(s):  
Reynolds Number ◽  
Pressure Gradient ◽  
Numerical Study ◽  
Adverse Pressure Gradient ◽  
Navier Stokes ◽  
Test Cases ◽  
Pressure Gradients ◽  
Flow Conditions ◽  
Transition Models ◽  
High Reynolds

A numerical study has been performed to compare the overall performance of three transition models when used with an industrial Navier-Stokes solver. The three models investigated include two experimental correlations and an integrated eN method. Twelve test cases in realistic turbomachinery flow conditions have been calculated. The study reveals that all the three models can work numerically well with an industrial Navier-Stokes code, but the prediction accuracy of the models depends on flow conditions. In general, all the three models perform comparably well to predict the transition in weak or moderate adverse pressure-gradient regions. The two correlations have the merit if the transition starts in strong favorable pressure-gradient region under high Reynolds number condition. But only the eN method works well to predict the transition controlled by strong adverse pressure gradients. The three models also demonstrate different capabilities to model the effects of turbulence intensity and Reynolds number.

A supersonic turbulent boundary layer in an adverse pressure gradient

1990 ◽  
Vol 211 ◽  
pp. 285-307 ◽  
Author(s):  
Emerick M. Fernando ◽  
Alexander J. Smits
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Pressure Distribution ◽  
Large Scale ◽  
Adverse Pressure Gradient ◽  
Large Scale Structures ◽  
Streamline Curvature ◽  
The Mean ◽  
Scale Structures

This investigation describes the effects of an adverse pressure gradient on a flat plate supersonic turbulent boundary layer (Mf ≈ 2.9, βx ≈ 5.8, Reθ, ref ≈ 75600). Single normal hot wires and crossed wires were used to study the Reynolds stress behaviour, and the features of the large-scale structures in the boundary layer were investigated by measuring space–time correlations in the normal and spanwise directions. Both the mean flow and the turbulence were strongly affected by the pressure gradient. However, the turbulent stress ratios showed much less variation than the stresses, and the essential nature of the large-scale structures was unaffected by the pressure gradient. The wall pressure distribution in the current experiment was designed to match the pressure distribution on a previously studied curved-wall model where streamline curvature acted in combination with bulk compression. The addition of streamline curvature affects the turbulence strongly, although its influence on the mean velocity field is less pronounced and the modifications to the skin-friction distribution seem to follow the empirical correlations developed by Bradshaw (1974) reasonably well.

scholarly journals Studi Numerik Steady RANS Aliran Fluida di Dalam Asymmetric Diffuser

2017 ◽  
Vol 4 (1) ◽  
pp. 20 ◽  
Author(s):  
Yiyin Klistafani
Keyword(s):  
Fluid Flow ◽  
Pressure Gradient ◽  
Numerical Study ◽  
Maximum Velocity ◽  
Turbulence Models ◽  
Adverse Pressure Gradient ◽  
Positive Pressure ◽  
Front Wall ◽  
Human Beings ◽  
Vertical Side

Research on fluid flow becomes a necessity to develop technology and for the welfare of human beings on earth. One of them is study of fluid flow in the diffuser. The example of diffuser application is used as a flue gas duct in the car or motorcycle. In addition, diffuser is also applied in air conditioning systems. Diffuser is a construction that able to control the behavior of the fluid. The increasing of cross section area in the diffuser will generate a positive pressure gradient or also called adverse pressure gradient (APG). The greater APG that happens, the greater energy required by the fluid to fight it, because APG will lead to separation. This study aimed to evaluate the numerical fluid flow in the asymmetric diffuser with divergence angle (θ) = 10 ° (upper wall) and widening one vertical side (α) of 20 ° (front wall). The Reynolds number is 8.7 x 104 by high inlet diffuser and the maximum velocity at the inlet diffuser. Turbulence models used are standard k-ɛ, realizable k-ε, and shear stress transport (SST) k-ω. Numerical study of steady RANS used Fluent 6.3.26 software. Results of numerical visualizations show that huge vortex established in diffuser, that’s why performance of diffuser is not optimal. In addition the location of separation point shown by SST k-ω is earlier than other turbulence models (standard k-ε and realizable k-ε).

Numerical Investigation of Corner Separation on Compressor Cascade

2013 ◽  
Author(s):  
Jing Ling ◽  
Xin Du ◽  
Songtao Wang ◽  
Zhongqi Wang
Keyword(s):  
Pressure Gradient ◽  
Pressure Distribution ◽  
Separation Zone ◽  
Adverse Pressure Gradient ◽  
Compressor Cascade ◽  
Suction Surface ◽  
Corner Separation ◽  
Pressure Point ◽  
Static Pressure Distribution ◽  
Blade Thickness

This paper studied the effects of suction surface corner separation on the aerodynamic performance and the effects of the blade parameters on suction surface corner separation in rectangular cascade. Corner separation alters the static pressure distribution on the suction surface, establish a C-Shape pressure distribution along spanwise, compared with open separation, closed separation intensifies the C-Shape pressure distribution, increases the streamwise adverse pressure gradient on the suction surface after the lowest pressure point. The diffusion capability in a closed separation was significantly lower than in an open separation on the separation zone, loss was larger than open separation. The changes of blade parameters have great effects on corner separation, not only affect the scale of separation zone, even they will change the separation form. This study show that with the increase of the blade thickness, the maximum thickness position moving afterwards and the increase of the deflection of mean camber line, the streamwise adverse pressure gradient on the suction surface after the lowest pressure point increase, the scale of separation zone increase, even the separation type changes from open separation to closed separation.

Aerodynamic performance analysis and optimization of a turbine duct with low degree of partial admission

2017 ◽  
Vol 232 (5) ◽  
pp. 988-1001 ◽  
Author(s):  
Xiuming Sui ◽  
Wei Zhao ◽  
Xiaolei Sun ◽  
Weiwei Luo ◽  
Qingjun Zhao
Keyword(s):  
Pressure Gradient ◽  
Negative Impact ◽  
Numerical Study ◽  
Flow Behavior ◽  
Adverse Pressure Gradient ◽  
Partial Admission ◽  
Duct Geometry ◽  
Inlet Conditions ◽  
Comparative Results ◽  
The Impact

A partial admission turbine duct with outlet-to-inlet area ratio greater than unity can increase the admission degree of the downstream turbine stage and, thus improve the performance of a multistage turbine with a low partial admission degree. However, the upstream flow structures of ducts, such as secondary flow, especially the circumferential nonuniformities originating from the effect of the partial admission, make the flow in ducts complex. The complexity of the flow has a negative impact on the performance of ducts. In the present investigation, numerical study of the flow behavior within ducts is done to evaluate the effect of the partial admission on the performance of the ducts. The study is carried out with regard to two cases, i.e. which are with the same duct geometry but are at different working conditions to highlight the impact of partial admission on the performance of ducts. Case 1 is used as baseline. It is designed based on circumferential mass-averaged flow conditions at ducts inlet. It causes the circumferential nonuniformities originating from the partial admission to have no impact on the performance of case 1. Case 2, which considers partial admission, is compared with case 1 to know the impact of the partial admission on the performance of ducts, and to give guidelines to design a duct for the partial admission turbines. Since the duct inlet conditions is a result of the interaction between partial admission turbine and duct, a straightforward way to consider the effect of the partial admission is to simulate the flows in ducts and upstream turbines contemporaneously. Comparative results indicate that the mixing of main flow in the admitted channel and the windage fluid from the unadmitted channel occurs at the duct inlet close to the duct circumferential wall. The adverse pressure gradient of case 2 in that region becomes larger than that of case 1. As a result, the flow separates at that region deteriorating the performance of ducts. Based on the simulation results of the previous cases, case 2’s circumferential wall surface, which is along the gas swirling direction is shrunk to accelerate the flow and, thereby, overcome the adverse pressure gradient imposed by the effect of the partial admission. The results show that the separation is restrained and the decrease in total pressure loss is 52.9%.

scholarly journals A numerical study of strained three-dimensional wall-bounded turbulence

2000 ◽  
Vol 416 ◽  
pp. 75-116 ◽  
Author(s):  
G. N. COLEMAN ◽  
J. KIM ◽  
P. R. SPALART
Keyword(s):  
Pressure Gradient ◽  
Boundary Layers ◽  
Numerical Study ◽  
Three Dimensional ◽  
Adverse Pressure Gradient ◽  
Model Testing ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Dimensional Boundary ◽  
The Mean

Channel flow, initially fully developed and two-dimensional, is subjected to mean strains that emulate the effect of rapid changes of streamwise and spanwise pressure gradients in three-dimensional boundary layers, ducts, or diffusers. As in previous studies of homogeneous turbulence, this is done by deforming the domain of a direct numerical simulation (DNS); here however the domain is periodic in only two directions and contains parallel walls. The velocity difference between the inner and outer layers is controlled by accelerating the channel walls in their own plane, as in earlier studies of three-dimensional channel flows. By simultaneously moving the walls and straining the domain we duplicate both the inner and outer regions of the spatially developing case. The results are used to address basic physics and modelling issues. Flows subject to impulsive mean three-dimensionality with and without the mean deceleration of an adverse pressure gradient (APG) are considered: strains imitating swept-wing and pure skewing (sideways turning) three-dimensional boundary layers are imposed. The APG influences the structure of the turbulence, measured for example by the ratio of shear stress to kinetic energy, much more than does the pure skewing. For both deformations, the evolution of the Reynolds stress is profoundly affected by changes to the velocity–pressure-gradient correlation Πij. This term – which represents the finite time required for the mean strain to modify the shape and orientation of the turbulent motions – is primarily responsible for the difference (lag) in direction between the mean shear and the turbulent shear stresses, a well-known feature of perturbed three-dimensional boundary layers. Files containing the DNS database and model-testing software are available from the authors for distribution, as tools for future closure-model testing.

An Analytical Method for the Design of Two-Dimensional Contractions

1964 ◽  
Vol 68 (637) ◽  
pp. 59-62 ◽  
Author(s):  
W. T. F. Lau
Keyword(s):  
Pressure Gradient ◽  
Pressure Distribution ◽  
Analytical Method ◽  
Complex Potential ◽  
Adverse Pressure Gradient ◽  
Main Stream ◽  
Two Dimensional ◽  
Uniform Stream

SummaryAn analytical method is presented for the design of two-dimensional contractions. In this method, the complex potential of the flow of an infinite row of equally spaced line sources normal to a uniform stream is obtained. By adjusting the strength of the sources, the streamlines of the main stream are used as boundaries of two-dimensional contractions of various contraction ratios. It is found that, in all cases, there is a region in the main stream between two neighbouring sources in which the speed of flow increases monotonically along streamlines. Contractions formed by any of the streamlines in this region would therefore have favourable pressure distribution along their boundaries except for very small adverse pressure gradient at the inlet and outlet which are due to the introduction of parallel sections.

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