Wall Pressure Values Research Articles

Supersonic cooling film flow evolution on a curved wall under hypersonic flow

Curvature plays a crucial role in evolving supersonic cooling film flow-field structures. Flow-field structural images were captured using nanotracer-based planar laser scattering,, and wall pressure values were obtained using experimentally validated numerical simulations. A supersonic cooling film is tangentially injected at the Mach number of Maj = 2.3 into a laminar boundary layer at a mainstream of Ma = 6. The supersonic cooling film inhibits mixing-layer instability on the convex curved wall (CV) and promotes it on the concave curved wall (CC). After increasing the total incoming pressure, the reduction ratio of static pressure (RSP) between the supersonic cooling film and the mainstream flow causes a delay in the position of the mixing-layer instability, smaller-scale vortex structures, and decreased flow velocity of the typical vortex structures on the CC and CV. The wall pressure increases for the CV and decreases for the CC, indicating that the supersonic cooling film suppresses the changes in wall pressure due to curvature. The supersonic cooling film suppresses the decrease in the impulses for bulk dilatation (Ip) due to convex curvature and the increase in Ip due to concave curvature. The growth rate of Ip on the CC increases from −15% to −8% and decreases on the CV from 31% to 12% in the bending impulse (IΦ) range of |IΦ| = 1.337–3.624 for a total inlet pressure of 0.5 MPa. Increasing the RSP could control the Ip values on curved surfaces more effectively. The results of this study can be applied to cooling the infrared optics window on hypersonic vehicles.

Inversion and reconstruction of supersonic cascade passage flow field based on a model comprising transposed network and residual network

A data-driven model comprising a transposed network and a residual network is proposed to predict the flow field structure of the supersonic cascade passage by measuring the wall pressure of the cascade passage. This model is based on the close relationship between the wall pressure values of the supersonic cascade passage and the flow field structure. Wind tunnel experiments of the supersonic cascade passage were conducted to obtain real experimental data. The transposed network, which is the first part of the model, consists of transposed convolution, normal convolution, and fully connected layers. However, the mapping ability of the transposed network between the wall pressure values and the cascade passage flow field structures was insufficient. The maximum relative error by the transposed network in predicting the position of the leading edge of the shock train was 8.5%. Therefore, the residual network was introduced as the second part of the model to achieve end-to-end super-resolution and improve the mapping ability of the model. After training, the residual network reduced the maximum relative error of the position prediction of the leading edge of the shock train to 3.5%. In the testing set, the prediction results of the model indicated that the movement of the leading edge of the shock train can be distinguished well. Furthermore, a combination of the two networks revealed the mapping relationship between the wall pressure of the supersonic cascade passage and the flow field structure. Thus, the results of this study lay a good foundation for the subsequent determination of the flow field stability margin.

Effects of Micro jets on the Flow Field of the Duct with Sudden Expansion

This paper presents the results of an experimental investigation to study the effectiveness of the control jets to control base pressure in rapidly expanded circular tubes. Four tiny jets of 1 mm orifice diameter located at ninety degrees interval in cross shape along a pitch circle diameter of 1.3. The Mach number, the L/D ratio, and the area ratio of the study were 2.8, from 1 to 10, and 4.84, respectively. The nature of the flow field, the development of the flow in the duct, as well as the static wall pressure distribution in the duct was measured and discussed. The results indicate that the tiny jets can be used as an active dynamic controller for the base pressure. The wall pressure distribution is not adversely influenced by the small jets. From the present investigation, it is evident that for a given Mach number and nozzle pressure ratio one can identify the minimum duct L/D needed for the flow remained attached with the wall of the duct. The trend for the duct length L = 5D seems to show different results, due to the influence of back pressure and the peak pressure values are also less than that those were for higher L/D ratios, especially in respect of L/D = 5. Further, the flow field has smoothened in the duct, and wall pressure values with and without micro jets are identical. This trend continues until L/D = 4, then later for lower L/Ds like L/D = 3, the flow seems to be attached at higher NPRs. But for lower NPRs the flow is not attached

Effects of the confinement on wall pressure, interfacial tension, and excess adsorption at the nanocylindrical wall

In this article, a hard sphere fluid confined between two homocentric cylinders which formed a bicylindrical pore has been investigated. Our aim is investigation of the effect of an outer cylinder on the values of wall pressure, interfacial tension, and excess adsorption of fluid at a convex nanocylindrical wall, inner wall. To investigate this effect, the modified fundamental measure theory (MFMT) used. To do so at first we presented a general solution for weighted density integrals in cylindrical coordinate which is applicable for infinite and infinite lengths of cylindrical pore, bicylindrical pore, cylindrical wall, and even truncated cone. In the second step, the wall pressures, interfacial tensions, and excess adsorptions at a convex nanocylindrical wall are obtained for confined fluids in bicylindrical pores and compared with those values for bulk fluids. Our results showed that confinement leads to an oscillatory behavior for wall pressure, interfacial tension, and excess adsorption of the fluid at the wall. The reason for these oscillations lies in structural changes that occur for a fluid as a result of confinement. Variation of the type of interaction of inner wall with fluid from hard to attractive one can reverse the behavior of interfacial tension and adsorption versus size. Also in some cases, it changes their signs while the change in the type of interaction of the outer wall only leads to an increase in amplitudes of the oscillations.

Numerical Investigation of the Aerodynamic and Infrared Radiation Characteristics of Spherical Convergent Flap Nozzles

AbstractA number of numerical predictions are performed to evaluate the aerodynamic and infrared radiation characteristics of spherical convergent flap nozzles (SCFN). The accuracy of the computations was verified by comparing the calculated wall pressure values to experimentally measured ones. The prediction results show that the vortices produced by the secondary flow at the corner of the divergent section are the main factor to produce thrust loss without any vectoring action. Compared to the axisymmetric nozzle, the SCFN caused up to 1.86% thrust loss and 3% flow rate loss. The yaw angle had no effect on the inner flow field in the divergent section and the exhaust flow because the yaw vector turning is achieved by gimballed subsonic flow. The maximum thrust losses were only 1 and 0.69%, which were caused by the pitch and yaw vector, respectively. The aerodynamic vector angle was approximately consistent with the turning angle due to geometric deflection of SCFN. With a 15° geometric pitch angle, the ...

On the Capability of PIV-Based Wall Pressure Estimation for an Impinging Jet Flow

A PIV-based pressure estimation methodology is used to compute the wall pressure from the velocity field of a turbulent impinging jet flow. A simplified formulation (2D-2C) is applied to velocity fields issued from PIV data. The ability of the method to qualitatively estimate the wall pressure signature of a 3D unsteady impinging jet flow using only two velocity components in a plane is demonstrated. Nevertheless, the 2D flow assumption used in the context of planar measurements involves an underestimation of the wall pressure values all along the radial direction. The formulation based on the full integral formalism (3D-3C), computed from DNS data without any assumption on the flow, provides a reference solution. The contributions of the surface and volume integrals to the pressure coefficient are assessed. It is shown that the most important contribution to the wall pressure comes from the volume integral. Then the underestimation observed for the simplified formulation is mostly linked with the assumptions considered for the source term computation. The effect of each assumption is quantitatively analysed with the help of the DNS data and some ways to improve the simplified methodology are finally proposed.

Numerical Simulation of the Cold Gas Dynamic Spray Process

A computational fluid dynamic (CFD) model of the cold gas dynamic spray process is presented. The gas dynamic flow field and particle trajectories within an oval-shaped supersonic nozzle as well as in the immediate surroundings of the nozzle exit, before and after the impact with the target plane, are simulated. Predicted nozzle wall pressure values compare well with experimental data. In addition, predicted particle velocity results at the nozzle exit are in qualitative agreement with those obtained using a side-scatter laser Doppler anemometer (LDA). Details of the pattern of the particle release into the surroundings are visualized in a convenient manner.

Flow parameters in normal left coronary artery tree. Implication to atherogenesis

The dominant haemodynamic flow parameters of wall pressure (WP), wall shear stress (WSS), molecular viscosity and the spatial gradients: wall pressure gradient (WPG) and wall shear stress gradient (WSSG) along the normal human left coronary artery (LCA) tree are numerically analyzed in relation to atheronegenesis. The LCA tree includes the left main coronary artery, the left anterior descending branch, the left circumflex branch and their major branches. Spatial differentiation indicates that low values of WP (locally), WPG, WSS, WSSG and high molecular viscosity appear opposite flow dividers and this probably correlates to atherosclerosis localization.

Lateral and vertical pressures in two different full-scale grain bins during loading Presiones laterales y verticales durante el llenado de diferentes silos para granos

Lateral and vertical floor pressures were measured in two different corrugated-walled steel grain bins using load cells mounted on the floor and walls of the bin. Bin one was 12.8 m in diameter and 17.1 m tall and bin two was 11.0 m in diameter and 14.0 m tall. Tests were conducted with corn. In the 12.8 m diameter bin the largest average lateral wall pressure was 28.2 kPa at a grain depth of 15.2 m, while in the 11.0 m diameter bin the largest average lateral pressure was 26.9 kPa at a grain depth of 11.9 m. Design standard EP433 produced only slightly more conservative lateral wall pressure values at larger grain heights than design standard DIN1055. In both the 12.8 m and 11.0 m diameter bins a significant decrease in vertical floor pressures was measured near the wall of the bins (> 0.85 r), while at the other load cell locations the vertical floor pressure values were very similar in magnitude. In design, both EP433 and DIN1055 underestimated the vertical floor pressures which were measured in these bins. Based on these results some thought should be given to designing metal bins for both 'initial' conditions in which grain slides along 'virgin' materials and have a high coefficient of friction, and for 'worn' conditions in which oils and waxes have been deposited on the bin walls and thus produce a low coefficient of friction.

Application of computational fluid dynamics to pitch/yaw thrust vectoring spherical convergent flap nozzles

The Computational Fluid Dynamics (CFD) methodology required to model accurately the complex threedimensional flow generated by vectoring nozzles is discussed and the tools used in this methodology are described. These tools are then applied to calculate the flowfield in two Spherical Convergent Flap (SCF) nozzle configurations. The accuracy of the computations is calibrated by comparing the calculated wall pressure values to those experimentally measured in model tests where the thickness of incoming boundary layer was negligible. It is shown that Euler calculations are adequate for the prediction of pressure and, hence, thrust for these nozzles.

Comparison of a two-dimensional shock impingement computation with experiment

Results of computations of two-dimensional viscous blunt-body flowfields with an impinging shock wave, with a time-dependent finite-difference method employed to solve the complete set of Navier-Stokes equations, are compared with experimental results. The experimental results were obtained in a 20-inch hypersonic tunnel with a planar shock impinging on the cylindrical leading edge of a fin, hence with the shock parallel to the centerline of the leading edge, so that type III and type IV interference patterns were generated. Close agreement is found. The overall effects of smoothing and grid size on the calculations are determined. A 31 x 51 mesh is adequate for wall pressure values (except in peaked regions).

Physics of root growth.

THE elongation of a plant cell involves the yielding of the cell wall under the action of tensile stresses in the wall1. The rate of elongation, R, can be expressed simply as R=mW, where m is the extensibility of the cell wall material and W is the wall pressure. Changes in either m or W have been used to explain the effect of biochemical factors on the growth rate of plant cells2,3. Cell growth is also affected by the physical environment and this becomes particularly important in the case of plant roots where soil water potential and the mechanical resistance of the soil to deformation can become rate controlling. Working with 3-5 day old radicles of Pisum sativum, growing in soil cores, we have obtained values of wall pressure in terms of these two properties, and we find that the rate of root elongation can be described by a simple extensibility equation.