<P >· What does the STAR in STAR-CD and STAR-HPC stand for?<p></p></P>
<P ><B>S</B>imulation of <B>T</B>urbulence in <B>A</B>rbitrary <B>R</B>egions.<p></p></P>
<P >A little known historical fact is that other names were considered for the code before the name STAR-CD was chosen:<p></p></P>
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<P ><p> </p></P>
<P >However, these acronyms were, for unknown reasons, deemed unacceptable.<p></p></P>
<P >Back to FAQ list <p></p></P>
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<P >· How much memory do pro*am and STAR use?<p></p></P>
<P >pro*am: Approximately 100 Mb per 500k cells.<p></p></P>
<P >STAR: <BR>Approximately 45 Mb per 100k hexahedral cells.<BR>Approximately 50 Mb per 100k trimmed cells mesh.<BR>Approximately 75 Mb per 100k tetrahedral cells.<p></p></P>
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<P >· What is the reference pressure?<p></p></P>
<P >The reference pressure is used to maximize the precision of calculated pressure gradients.<p></p></P>
<P >All pressure values stored in the .pst file and in internal arrays are stored relative to the reference pressure for each material type.<p></p></P>
<P >All input requested by the user interface for pressures will be relative to the reference pressure.<p></p></P>
<P >Calculations within the code that are dependent on absolute pressures use the stored relative pressure added to the reference pressure.<p></p></P>
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<P >· How does the value of the reference pressure influence the analysis?<p></p></P>
<P >o Models that contain no pressure boundaries:<p></p></P>
<P >Any fluid stream in a steady state analysis that contains no pressure boundaries will "pin" the pressure field such that the relative pressure at the pressure reference cell is identically zero. i.e. the absolute pressure at the pressure reference cell will be the reference pressure.<p></p></P>
<P >o Models that contain pressure boundaries:<p></p></P>
<P >Any fluid stream in a steady state analysis that does contain a pressure boundary or any transient analysis will not "pin" the pressure at the reference cell. However the pressure at the reference cell and all other cells is still stored relative to the reference pressure. i.e. the absolute pressure at the pressure reference cell will be the stored relative pressure plus the reference pressure.<p></p></P>
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<P >· What happens to the reference pressure when there are multiple fluid streams?<p></p></P>
<P >If the fluid streams pass mass it is convenient that the value of the pressure reference be the same for each stream. <p></p></P>
<P >For example, an explicit multiple reference frame problem is set up using separate material types. However, these separate fluid streams actually can pass mass back and forth. Using the same pressure reference value makes the continuity of the pressure field visible even when loading relative pressures. If the pressure reference values are different then continuity of the pressure field can only be observed by loading absolute pressures.<p></p></P>
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<P >· What is the temperature datum?<p></p></P>
<P >As with pressure, temperature is stored relative to a reference value. T-Datum is that value. However, unlike pressure, all references to temperature in the user interface are in absolute units (K). The only time the user is likely to encounter a relative temperature is in the user subroutines. The user should examine the "nom.inc" file to find out if the temperature arrays or values used in a user subroutine are absolute or relative.<p></p></P>
<P >The value of the temperature datum is also used during ISOBARIC analyses. In an isobaric analysis the user is supplying a Bulk Modulus for the variation of density with temperature and a baseline density. The code assumes that the baseline density exists at the datum temperature.<p></p></P>
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<P >· How do velocity, density, temperature and the pressure field interact at INLET boundaries?<p></p></P>
<P >o Incompressible flows: <p></p></P>
<P >As rho is constant and equal to the fluid density, the value of rho specified at the inlet is ignored. The temperature value at the inlet is kept constant, which results in a constant mass flow entering the inlet.<p></p></P>
<P >o Compressible flows:<p></p></P>
<P >Two possible situations arise, namely subsonic flow and supersonic flow. The use of the fixed mass/fixed velocity switch in the inlet region definition only affects the inlet condition when it is subsonic.<p></p></P>
<P >§ Subsonic flow:<p></p></P>
<P >§ Flow switch set to "Fixed Mass Flow" (default):<p></p></P>
<P >This means that a constant mass flow will be maintained at the inlet. This is achieved as follows - the temperature value is kept constant at the specified value. The density value is evaluated at every iteration (using the Ideal Gas Law) and allowed to change if it differs from the supplied region value. This can happen if the inlet value for rho has been incorrectly estimated or the resulting flow field has a variable density.<p></p></P>
<P >The velocity is then adjusted based on the new values to conserve the mass flow. An additional option called the "Fixed Angle" determines whether the normal component of velocity is adjusted (Fixed Angle=Off) or whether all three components are adjusted but the original vector direction is maintained (Fixed Angle=On). <p></p></P>
<P >§ Flow switch set to "Fixed Velocity":<p></p></P>
<P >This means that the specified inlet velocity will remain fixed. In this case temperature is again fixed at the given boundary value. Density is allowed to change based on the Ideal Gas Law and for the same reasons given above. The mass flow is then adjusted based on continuity.<p></p></P>
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<P >For supersonic flow, the the specified density and velocity values at the inlet remain unchanged.<p></p></P>
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