VDI 4675 BLATT 1
Balance-based averaging of inhomogeneous flow fields - Introduction
|Publication Date:||1 September 2012|
|ICS Code (Flow in closed conduits):||17.120.10|
|ICS Code (Energy and heat transfer engineering in general):||27.010|
On one hand the further development of experimental and computational methods for inhomogeneous flow fields is giving a better understanding of temporally and spatially variable flow processes and on this basis allowing to draw conclusions affecting the design of the machines and apparatus involved. On the other hand, before a global evaluation can be made of flow in driving or driven machines or in processing installations, the inhomogeneous fields for velocity vector, pressure, enthalpy, etc. will need to be expressed in averaged field quantities and corresponding numbers. In connection with flow analyses and acceptance measurements, for example, this is indispensable.
Normally use is made of balances in order to obtain global evaluation quantities from calculated or measured quantities. If averaged field quantities are to be substituted in the balances in place of the temporal and spatial distributions, these will be best obtained directly from balances. The present guideline is concerned with these "balance-based" averaged field quantities and numbers.
However, as will be shown, more balances and thermodynamic relationships would need to be satisfied here than can be included in the calculation of the individual averaged field quantities. Depending on which balance equations are selected for averaging, different averaged field quantities would be obtained. Simply requiring that averaging should be carried out by balancing would not of itself therefore result in an unambiguous and uniform averaging procedure. This is achieved here by the described division into conservation and non-conservation balance equations.