Further Developments in the Aerodynamic Analysis of Unsteady Supersonic Cascades—Part 1: The Unsteady Pressure Field

1977 ◽  
Vol 99 (4) ◽  
pp. 509-516 ◽  
Author(s):  
J. M. Verdon
Keyword(s):  
Velocity Potential ◽  
Pressure Field ◽  
Supersonic Stream ◽  
Axial Velocity Component ◽  
Unsteady Pressure ◽  
Pressure Distributions ◽  
Successive Solution ◽  
Construction Procedure ◽  
Present Procedure ◽  
Dependent Variables

This paper presents, in two parts, a theoretical investigation of the aerodynamic response produced by an oscillating cascade placed in a supersonic stream with subsonic axial velocity component. Predictions are based on the successive solution of two linear boundary value problems which treat the velocity potential and the pressure, respectively, as basic dependent variables. A solution for the potential has been reported earlier and is used here to provide upper surface blade pressure distributions. This information serves as a boundary condition for the second problem. The solution for the unsteady pressure field, described in Part 1, is obtained by a construction procedure which parallels that used earlier to determine the potential. With the present procedure, blade pressure difference distributions and aerodynamic coefficients are accurately and efficiently determined for both subresonant and superresonant blade motions. Supersonic resonance phenomena and selected numerical results are discussed in Part 2 of the paper.

scholarly journals An Unsteady Lifting Surface Theory for Ducted Fan Blades

1991 ◽  
Author(s):  
Ray M. Chi
Keyword(s):  
Velocity Potential ◽  
Three Dimensional ◽  
Surface Theory ◽  
Unsteady Pressure ◽  
Aerodynamic Pressure ◽  
Unsteady Aerodynamic ◽  
Ducted Fan ◽  
Pressure Distributions ◽  
Lifting Surface ◽  
Perturbation Velocity

A frequency domain lifting surface theory is developed to predict the unsteady aerodynamic pressure loads on oscillating blades of a ducted subsonic fan. The steady baseline flow as observed in the rotating frame of reference is the helical flow dictated by the forward flight speed and the rotational speed of the fan. The unsteady perturbation flow, which is assumed to be potential, is determined by solving an integral equation that relates the unknown jump in perturbation velocity potential across the lifting surface to the upwash velocity distribution prescribed by the vibratory motion of the blade. Examples of unsteady pressure distributions are given to illustrate the differences between the three dimensional lifting surface analysis and the classical two dimensional strip analysis. The effects of blade axial bending, bowing (i.e., circumferential bending) and sweeping on the unsteady pressure load are also discussed.

An Unsteady Lifting Surface Theory for Ducted Fan Blades

1993 ◽  
Vol 115 (1) ◽  
pp. 175-188 ◽  
Author(s):  
R. M. Chi
Keyword(s):  
Velocity Potential ◽  
Three Dimensional ◽  
Surface Theory ◽  
Unsteady Pressure ◽  
Aerodynamic Pressure ◽  
Unsteady Aerodynamic ◽  
Ducted Fan ◽  
Pressure Distributions ◽  
Lifting Surface ◽  
Perturbation Velocity

A frequency domain lifting surface theory is developed to predict the unsteady aerodynamic pressure loads on oscillating blades of a ducted subsonic fan. The steady baseline flow as observed in the rotating frame of reference is the helical flow dictated by the forward flight speed and the rotational speed of the fan. The unsteady perturbation flow, which is assumed to be potential, is determined by solving an integral equation that relates the unknown jump in perturbation velocity potential across the lifting surface to the upwash velocity distribution prescribed by the vibratory motion of the blade. Examples of unsteady pressure distributions are given to illustrate the differences between the three-dimensional lifting surface analysis and the classical two-dimensional strip analysis. The effects of blade axial bending, bowing (i.e., circumferential bending), and sweeping on the unsteady pressure load are also discussed.

scholarly journals Diffraction of plane elastic waves by a crack, with application to a problem of brittle fracture

1963 ◽  
Vol 3 (3) ◽  
pp. 325-339 ◽  
Author(s):  
M. Papadopoulos
Keyword(s):  
Elastic Waves ◽  
Scattered Field ◽  
Velocity Potential ◽  
Elastic Solid ◽  
Step Function ◽  
Free Surface Waves ◽  
Dependent Variables ◽  
Smooth Plane ◽  
New Feature ◽  
Set Up

AbstractA crack is assumed to be the union of two smooth plane surfaces of which various parts may be in contact, while the remainder will not. Such a crack in an isotropic elastic solid is an obstacle to the propagation of plane pulses of the scalar and vector velocity potential so that both reflected and diffracted fields will be set up. In spite of the non-linearity which is present because the state of the crack, and hence the conditions to be applied at the surfaces, is a function of the dependent variables, it is possible to separate incident step-function pulses into either those of a tensile or a compressive nature and the associated scattered field may then be calculated. One new feature which arises is that following the arrival of a tensile field which tends to open up the crack there is necessarily a scattered field which causes the crack to close itself with the velocity of free surface waves.

An Approximate Solution for Incompressible Flow About an Ellipsoid Near a Plane Wall

1950 ◽  
Vol 17 (2) ◽  
pp. 154-158
Author(s):  
Phillip Eisenberg
Keyword(s):  
Approximate Solution ◽  
Velocity Distribution ◽  
Closed Form ◽  
Incompressible Flow ◽  
Velocity Potential ◽  
Plane Wall ◽  
Wall Effect ◽  
Pressure Distributions

Abstract Using the method of successive images, an approximate solution for the velocity potential is obtained in closed form for incompressible flow about an ovary ellipsoid near a plane wall. The velocity distribution is computed from this solution in two ways. The first computation properly predicts differences in velocities on opposite half-meridians of the ellipsoid. A second method results in a symmetric velocity distribution but is useful for rapid estimates of the average wall effect. Pressure distributions calculated by this theory are compared with values measured on 4:1 and 6:1 ellipsoid models.

Unsteady Pressure Measurement on Oscillating Blade in Transonic Flow Using Fast-Response Pressure-Sensitive Paint

2017 ◽  
Author(s):  
Toshinori Watanabe ◽  
Toshihiko Azuma ◽  
Seiji Uzawa ◽  
Takehiro Himeno ◽  
Chihiro Inoue
Keyword(s):  
Surface Pressure ◽  
Transonic Flow ◽  
Aerodynamic Force ◽  
Fast Response ◽  
Pressure Sensitive Paint ◽  
Unsteady Pressure ◽  
Pressure Distributions ◽  
Pressure Sensitive ◽  
Unsteady Surface Pressure ◽  
Response Pressure

A fast-response pressure-sensitive paint (PSP) technique was applied to the measurement of unsteady surface pressure of an oscillating cascade blade in a transonic flow. A linear cascade was used, and its central blade was oscillated in a translational manner. The unsteady pressure distributions of the oscillating blade and two stationary neighbors were measured using the fast-response PSP technique, and the unsteady aerodynamic force on the blade was obtained by integrating the data obtained on the pressures. The measurements made with the PSP technique were compared with those obtained by conventional methods for the purpose of validation. From the results, the PSP technique was revealed to be capable of measuring the unsteady surface pressure, which is used for flutter analysis in transonic conditions.

Flow field behind a complex total pressure distortion screen

2019 ◽  
Vol 233 (14) ◽  
pp. 5075-5092
Author(s):  
M Sivapragasam
Keyword(s):  
Flow Field ◽  
Total Pressure ◽  
Design Methodology ◽  
Pressure Field ◽  
Alternative Interpretation ◽  
Interface Plane ◽  
Screen Design ◽  
Pressure Distributions ◽  
Water Jet Cutting ◽  
Distortion Index

The flow field behind a complex total pressure distortion screen is investigated experimentally and numerically. The distortion screen is designed using an established design methodology and fabricated by water-jet cutting technique. The distorted total pressure field behind the screen is quantified by a distortion index parameter, which is evaluated from computations and experiments for several values of inlet Mach number. The root-mean-square error between the target total pressure values and that achieved by the screen design at the aerodynamic interface plane is 4.75%. The evolution of the distorted total pressure field downstream of the screen is presented in detail in terms of radial and circumferential total pressure distributions and their gradients. An alternative interpretation of the distorted total pressure field is made by means of defining a total pressure flux existing behind the screen and expanding it using derivative-moment transformation technique. It is seen that the circumferential vorticity is a major contributing factor to the total pressure flux.

Unsteady Flow Structure on a Centrifugal Pump: Experimental and Numerical Approaches

2002 ◽  
Author(s):  
Jose´ Gonza´lez ◽  
Carlos Santolaria ◽  
Eduardo Blanco ◽  
Joaqui´n Ferna´ndez
Keyword(s):  
Numerical Model ◽  
Centrifugal Pump ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
Side Wall ◽  
Relative Effect ◽  
Pressure Transducers ◽  
Unsteady Pressure ◽  
Blade Passing Frequency ◽  
Wide Range

Both experimental and numerical studies of the unsteady pressure field inside a centrifugal pump have been carried out. The unsteady patterns found for the pressure fluctuations are compared and a further and more detailed flow study from the numerical model developed will be presented in this paper. Measurements were carried out with pressure transducers installed on the volute shroud. At the same time, the unsteady pressure field inside the volute of a centrifugal pump has been numerically modelled using a finite volume commercial code and the dynamic variables obtained have been compared with the experimental data available. In particular, the amplitude of the fluctuating pressure field in the shroud side wall of the volute at the blade passing frequency is successfully captured by the model for a wide range of operating flow rates. Once the developed numerical model has shown its capability in describing the unsteady patterns experimentally measured, an explanation for such patterns is searched. Moreover, the possibilities of the numerical model can be extended to other sections (besides the shroud wall of the volute), which can provide plausible explanations for the dynamic interaction effects between the flow at the impeller exit and the volute tongue at different axial positions. The results of the numerical simulation are focused in the blade passing frequency in order to study the relative effect of the two main phenomena occurring at that frequency for a given position: the blade passing in front of the tongue and the wakes of the blades.

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