Variable Area Flow Research Articles

Numerical investigation of a mono-tube damper with a shim stack

The objective of this paper is to investigate the operation of a mono-tube damper through the application of Computational Fluid Dynamics analysis to the piston and flows through a series of flexible shims which cover exits of the piston orifices. The shims and orifices combine to form a system of variable area flow paths of the damper in parallel with the permanent bleed orifices. Shim stack stiffness characteristics were obtained using experimental and Finite Element techniques. The deflection characteristics were non-linear and were highly dependent upon small gaps present between shims and the restraining bodies. With the nature of the shim deflection being highly complex the computational fluid dynamics models investigated the shim deflection using a global uniform displacement method and also a more representative displacement based upon the finite element shim modelling. It was observed that the global displacement models allowed radially inward flow to establish and also overpredicted pressure drops. Finite element analysis of the shims allowed accurate representation of flow paths to be simulated which closely matched experimental and mathematical predictions. The computational fluid dynamics analyses showed that the discharge velocity for the global shim offset is greater than that from a variable shim deflection calculation. The damper pressure drop is highly dependent upon the shape of the flow path formed by the shim deflection. The presence of sharp direction changes through the piston and valve assembly leads to increased damping rates and piston pressure drops.

Research on a novel variable-area optical fiber gas flow sensor

Based on the structure of the traditional variable area flow meter and the principle of the optical fiber measurement, this article designed a new type of fiber Bragg grating (FBG) gas flow sensor. The tapered tube of the sensor is mounted vertically, and the float inside the tube moves up and down under the effect of the airflow. The longitudinal displacement of the float is converted to the deflection of the cantilever which bonded FBG under the action of magnetic force. Thus the flow variation could be transformed into the deflection of the cantilever, resulting in the change of FBG wavelength and phase. By detecting the change of the optical signal, the gas flow can be derived. The experimental results show that the sensor has the characteristics of good linearity and fast response time. The proposed sensor can determine the flow of air within 1–6.5m3/h and the sensitivity of the sensor approximately reaches 0.22nm/(m3/h). By optimizing the parameters of the sensor, the sensitivity and the accuracy can be improved accordingly.

On the treatment of transient area variation in 1D discontinuous Galerkin simulations of train‐induced pressure waves in tunnels

SUMMARYTo simulate the pressure wave generated by a train travelling through a tunnel, we implement a discontinuous Galerkin (DG) method for the solution of the one‐dimensional equations of variable area flow. This formulation uses a spatial discretisation via Legendre polynomials of arbitrary degree, and the resulting semi‐discrete system is integrated using an explicit Runge–Kutta scheme. A simulation of subsonic steady flow in a nozzle shows that the scheme produces stable solutions, without the need for artificial dissipation, and that its performance is optimal for polynomial degrees between 5 and 7. However, when dealing with an unsteady area, we report the presence of numerical oscillations that are not due to the steep pressure fronts in the flow but rather to the projection of a moving area, with piecewise continuous derivatives onto a fixed grid. We propose a reformulation of the DG method to eliminate these oscillations that, put in simple terms, amount to splitting the integrals where the derivatives of the cross‐sectional area are discontinuous into subintegrals where they are continuous. The resulting method does not exhibit oscillations, and it is applied here to two practical cases involving train‐induced pressure waves in a tunnel. The first application is a validation of the DG method through comparison of its computational results with pressure data measured during transit at the Patchway tunnel near Bristol (UK). The second application is a study of the influence of the nose shape and length on the pressure wave gradients responsible for sonic boom at tunnel exit portals to show that the proposed modification is able to deal with realistic train shapes. Copyright © 2012 John Wiley & Sons, Ltd.

G802 フロート式面積流量計による流体密度測定の可能性について : 流量が未知の場合(G.S.8 流れの計測技術1)

G802 フロート式面積流量計による流体密度測定の可能性について : 流量が未知の場合(G.S.8 流れの計測技術1)

Real-time method for NO2 flow measurements

Measurements of NO(2) flows are made without requiring prior experimental calibration of the flow meter. A tapered, variable area flow meter with a diameter ratio scale is used to make the real-time NO(2) flow measurements. The necessary parameters and calculations used to determine the viscosity and density of the flowing N(2)O(4)2NO(2) gas are presented. The limits of error associated with these parameters and errors associated with controlled flow measurement conditions are considered. Disregarding the scale reading error, which depends on the flow meter utilized, the limits of error are found to yield a measurement error less than 7%.

Expansion Factors for Two Variable Area Flow Meters

Data acquired in the years 1958 to 1960 at the Naval Ship Engineering Center under sponsorship of the American Society of Mechanical Engineers are used to derive semiempirical equations for the performance of two variable area meters with both liquid and gas flow. As the measurements are put to a useage for which they were not intended, the data treatment is considered illustrative of the application of a flow equation derived by an analysis based upon a force and momentum balance. The hydraulic flow coefficient is expressed in terms of a function of (a) pressure drop divided by float weight and of (b) a dimensionless length ratio β for float position. Density ratio is used to modify the function of β to derive the expansion factor Y for gas flow as suggested by the analysis. Reasonable agreement between measured and derived values of Y is demonstrated, and approximate measures of the velocity profiles in the meter are derived from the correlation equations. One set of air tests at one float position in which the viscous influence number N was changed from 500,000 to 783,000 indicated (within this range) a possible insensitivity of the derived function of β to change of N.

Fluid Dynamic Problems Awaiting Solution

It is recommended that fluid dynamic problems related to specific phenomena of pulsating flow should be dealt with on the basis of non-dimensional parameters. Part I presents a survey of essential parameters. Recent research on self-induced pulsations and forced sinusoidal pulsating flow is reviewed. Investigation of the experimental results of these studies reveal crucial parameters, their correct choice and design. These few parameters are recommended as basic tools of analysis of more complex problems which are encountered in fluid flow measurement. In Part II peculiarities in flow and the behaviour of metering devices such as orifices, Venturis, or variable area flow meters are scrutinized. Some of these features, even under steady flow conditions, are not yet well understood. They should be fully explored in future studies as they may explain residual errors under pulsating flow conditions. Suggestions for future research are mainly concerned with flow conditions in the pipe line upstream of the metering device.