Pressure Fluctuations In Turbulent Flow Research Articles

Unsteady control of supersonic turbulent cavity flow based on resolvent analysis

We use resolvent analysis to develop a physics-based, open-loop, unsteady control strategy to attenuate pressure fluctuations in turbulent flow over a rectangular cavity with a length-to-depth ratio of $6$ at a Mach number of $1.4$ and a Reynolds number based on cavity depth of $10\,000$. Large-eddy simulations (LES) of the baseline uncontrolled flow reveal the dominance of Rossiter modes II and IV that generate high-amplitude unsteadiness via trailing-edge impingement and oblique shock waves that obstruct the free stream. To suppress the oscillations, we introduce three-dimensional unsteady blowing along the cavity leading edge. We leverage resolvent analysis as a linear model with respect to the baseline flow to guide the selections of the optimal spanwise wavenumber and frequency of the unsteady actuation input for a fixed momentum coefficient of 0.02. Instead of choosing the most amplified resolvent forcing modes, we seek a disturbance that yields sustained amplification of the primary response mode-based kinetic energy distribution over the entire cavity length. This necessary but not sufficient guideline for effective mean flow modification is evaluated using LES of the controlled cavity flows. The most effective control case reduces the pressure root mean square level up to $52\,\%$ along cavity walls relative to the baseline and is approximately twice that achievable by comparable steady blowing. Dynamic mode decomposition on the controlled flows confirms that the optimal actuation input indeed suppresses the formation of the large-scale Rossiter modes. It is expected that the present flow control guideline derived from resolvent analysis will also be applicable at higher Reynolds numbers with the aid of physical insights and further validation.

Experimental and Numerical Investigation of Flow Structures around Cylindrical Bluff Bodies

The understanding and quantitative prediction of velocity and pressure fluctuations in turbulent flows around such bluff bodies have been evolving over the years. The main aim of the present work is to investigate experimentally and numerically the flow field in the wake region of different bluff bodies such as circular, square and triangle cross section cylinders placed horizontally perpendicular to the uniform flow. The experimental studies were performed by Particle Image Velocimetry (PIV) method in an open water channel at Reynolds numbers 5000 and 10000 defined according to the characteristic lengths of the cylinders in the facilities of Selcuk University of Advanced Technology Research and Application Center in Turkey. The experimental results are compared to the numerical results obtained by means of transient simulation with LES turbulence model of ANSYS-Fluent Software. It is shown that the numerical and experimental results have a good agreement in respect of the instantaneous and time-averaged flow field patterns of vorticity, velocity component streamwise direction and streamline topology. In addition, drag coefficient of the geometries were also numerically calculated. For all geometries the wake length in x and y directions and size of the foci of the streamlines are decreasing by increasing Reynolds numbers in time-averaged results. The time-averaged flow patterns of both experimental and numerical results have considerable symmetry with respect to the centerline of each cylinder. Contours of the time-averaged stream wise velocity for Re=10000 demonstrate that the stagnation point around the symmetry plane moves further upstream for all cylinders in accordance with Re=5000. The maximum drag coefficient value was yielded for the square cross-section cylinder as 1.78 due to the sharp-edged geometry.

A Novel Scheme for Calculating Pressure Fluctuations Used in Lagrangian-Eulerian Particulate Dispersion Codes

A novel scheme for pressure fluctuations in turbulent flows is developed. The pressure fluctuations are sensitive parameter in some of the fluid phenomena. In the computational methods and modeling turbulence flow, the pressure fluctuations are eliminated after averaging of the Navier-Stokes equations, and only average pressure could be calculated. In this research, the Reynolds-averaged Navier-Stokes equations are computed using SIMPLE method. The Reynolds stress transport model (RSTM) is used to determine the Reynolds stresses and the flow details. The velocity fluctuations are simulated using the Kraichnan model. The Poisson equation for the pressure fluctuations is obtained by taking the divergence of the incompressible momentum equation and algebraic operations, and this equation is numerically solved by finite difference method. The effects of Reynolds number on the pressure fluctuations are studied.

Prediction of wall-pressure fluctuation in turbulent flows with an immersed boundary method

The objective of this paper is to assess the accuracy and efficiency of the immersed boundary (IB) method to predict the wall pressure fluctuations in turbulent flows, where the flow dynamics in the near-wall region is fundamental to correctly predict the overall flow. The present approach achieves sufficient accuracy at the immersed boundary and overcomes deficiencies in previous IB methods by introducing additional constraints – a compatibility for the interpolated velocity boundary condition related to mass conservation and the formal decoupling of the pressure on this surfaces. The immersed boundary-approximated domain method (IB-ADM) developed in the present study satisfies these conditions with an inexpensive computational overhead. The IB-ADM correctly predicts the near-wall velocity, pressure and scalar fields in several example problems, including flows around a very thin solid object for which incorrect results were obtained with previous IB methods. In order to have sufficient near-wall mesh resolution for LES and DNS computations, the present approach uses local mesh refinement. The present method has been also successfully applied to computation of the wall-pressure space–time correlation in DNS of turbulent channel flow on grids not aligned with the boundaries. When applied to a turbulent flow around an airfoil, the computed flow statistics – the mean/RMS flow field and power spectra of the wall pressure – are in good agreement with experiment.

Aero-Micro-Electromechanical System Sensor Arrays for Time Resolved Wall Pressure Measurements

Wall pressure and wall pressure fluctuations in turbulent flows are of interest in many engineering applications. This paper focuses on the design and fabrication of aero-micro-electromechanical system surface pressure sensor arrays and their application to wall pressure measurements on a wall-mounted cylinder. The sensor arrays have been developed to be highly sensitive and mounted flush with the measurement surface. Thus, dynamic properties of the sensors are not limited by tubing, and an accurate measurement of the wall pressure and its fluctuations becomes possible. The arrays introduced herein consist of a number of individual sensors, which feature a maximum sensitivity of 12 μV/(VPa) and a pressure resolution of up to 0.5 Pa. Employing six arrays (three different types) consisting of up to 13 individual pressure sensors, wall pressure measurements have been conducted at the University of Rostock at a Reynolds number of 200,000. The results prove that the developed sensor arrays are a powerful measurement tool for experimental fluid mechanics. The wall pressure measurement data obtained are in good agreement with the results of the laser Doppler anemometry measurements and large-eddy simulations, which are also presented herein.

Methods of near-wall pressure-fluctuation measurements in the presence of vibration

Near-wall pressure fluctuations in turbulent flows are of considerable interest in many engineering applications. We shall concentrate on a number of specific questions related to the resolution of components of wall pressure spectra. Our emphasis shall be on outstanding problems of turbulent pressure fluctuations in the presence of vibration. A study on the interaction of a transducer with wall vibration resulting from near-wall turbulent flows has been performed. Three methods are described for the study of spectral components of turbulent surface pressure in conditions of flow-induced vibration: the method of separation of turbulent and vibration signals; the method of a vibration-proof turbulent pressure transducer; and a modified method of vibration suppression. A method of low-frequency acoustic-noise suppression is also suggested.

Experimental and numerical investigation of turbulent flow induced pipe vibration in fully developed flow

Flow-induced pipe vibration caused by fully developed pipe flow has been observed but not fully investigated when turbulent flow prevails. This article presents experimental results that indicate a strong correlation between the volume flow rate and a measure of the pipe vibration. In this work, the standard deviation of the frequency-averaged time-series signal, measured using an accelerometer attached to the pipe, is used as the measure of pipe vibration. A numerical, fluid-structure interaction (FSI) model used to investigate the relationship between pipe wall vibration and the physical characteristics of turbulent flow is also presented. This numerical FSI approach, unlike commercial FSI software packages, which are based on Reynolds averaged Navier-Stokes flow models, is based on large eddy simulation (LES) flow models that compute the instantaneous pressure fluctuations in turbulent flow. The results from the numerical LES models also indicate a strong correlation between pipe vibration and flow rate. In general, the numerical simulations show that the standard deviation of the pipe wall vibration is proportional to the pressure fluctuations at the wall induced by the flow turbulence. This research, indicates that the pressure fluctuations on the pipe wall have a near quadratic relationship with the flow rate. Furthermore, the experimental results and the numerical modeling show that there is a definite relationship between the acceleration of the pipe (pipe vibration) and the flow rate. These last two concepts open possible avenues for the development of a non-intrusive flow sensor.

A review of velocity and pressure fluctuations in turbulent flows around bluff bodies

This paper is firstly a review of the theory for the changes in the velocity fluctuations in a turbulent floq as it passes around a bluff body with a simple shape such as prism or sphere. Detailed results are given for the ideal cases where the scale of the incident turbulence is much smaller or much larger than the body's diameter, but it is shown that the results are also applicable to many practical flows, including bluff bodies in the wake of others. This review gives new, simple derivations for the spectra and variances of velocity and pressure fluctuations near the surface of bluff bodies, showing why on different shapes of body and for different scales there are different distributions of pressure variance. A new approach is described for simulating realisations of the random velocity field, using the technique of ‘kinematic simulation’. Experimental results are also briefly reviewed for bluff bodies placed in homogeneous turbulence, and in inhomogeneous shear flows. The outstanding problem remains of understanding how incident turbulence interacts with the turbulence and vortex shedding in the wake of a bluff body, though there has been some progress in identifying and understanding some of the mechanisms.

A review of velocity and pressure fluctuations in turbulent flows around bluff bodies

This paper is firstly a review of the theory for the changes in the velocity fluctuations in a turbulent floq as it passes around a bluff body with a simple shape such as prism or sphere. Detailed results are given for the ideal cases where the scale of the incident turbulence is much smaller or much larger than the body's diameter, but it is shown that the results are also applicable to many practical flows, including bluff bodies in the wake of others. This review gives new, simple derivations for the spectra and variances of velocity and pressure fluctuations near the surface of bluff bodies, showing why on different shapes of body and for different scales there are different distributions of pressure variance. A new approach is described for simulating realisations of the random velocity field, using the technique of ‘kinematic simulation’. Experimental results are also briefly reviewed for bluff bodies placed in homogeneous turbulence, and in inhomogeneous shear flows. The outstanding problem remains of understanding how incident turbulence interacts with the turbulence and vortex shedding in the wake of a bluff body, though there has been some progress in identifying and understanding some of the mechanisms.

Measurements of Pressure Fluctuation in the Wake of Cylinder

With a view to observing pressure fluctuations in turbulent flow of fluid, a new apparatus was constructed by using a condenser microphone as a transducer with a ratio-discriminator. The frequency response of the apparatus was calibrated by means of Karman vortices produced by a circular cylinder. The Helmholtz resonance and the loss in the pressure duct were compensated electrically by a band-rejection filter and a high-frequency booster. By these devices, the overall frequency response of the pressure-measuring apparatus was made flat between 50 and 1500 cycles per second. Using the apparatus in combination with a single rotary type hot-wire anemometer, it proved succesful in determining the intensity of static pressure fluctuation as well as the correlation between pressure and velocity fluctuation. Consequently all the terms in the energy equation became measurable, and the energy equation for the fluctuating quantities was ascertained experimentally for the first time in the wake of a circular cylind...

Pressure Fluctuations in Turbulent Flow over a Flat Plate

The pressure fluctuations exerted on a flat plate by a turbulent boundary layer flow are investigated. The approximate dependence of the mean-square intensity, spatial scale, and frequency scale on Mach number and distance from transition point are estimated through the use of similarity arguments. The wave number spectrum of the pressure fluctuation distribution over the surface of the plate is expressed in terms of transforms of two-point velocity correlations and expressions are derived for the driving force exerted on a rectangular piston set in the surface of the plate. It is found that the integral over the boundary surface of the two-point quadratic correlation function of the pressure fluctuation should vanish, with the result that the mean-square force per unit area exerted on a large area of the surface should tend to zero as the area increases indefinitely. An idealized model of turbulent boundary layer flow is constructed and used to relate the spectrum and correlation function of the surface pressure distribution to the corresponding functions for a homogeneous turbulent flow. Application of the theory to Laufer's data on turbulent channel flow indicates that the dominant contribution to the pressure fluctuations should depend only on the mean velocity profile and the two-point quadratic correlation of the fluctuating velocity component perpendicular to the boundary surface. On the basis of the seriously incomplete data available the rms pressure fluctuation from this source is tentatively estimated. The treatment of the present paper is based on the assumptions of (1) adiabatic conditions, (2) small compressibility, and (3) slow rate of growth of the boundary layer.