Updates to the system will be described below.

UPDATES to the MULTALL based design system.

UPDATES to the MULTALL based design system.

21/3/2017 Add STAGEN-17.2 and MEANGEN-17.2.

The only difference is that MEANGEN now passes the gas constant and specific heat ratio to STAGEN as its first line of data. Previously they were set in STAGEN by default. The STAGEN data sets provided have been updated to allow for this and will no longer work with STAGEN-17.1.

26/5/2017 Add MULTALL-OPEN-17.4, STAGEN-17.3 and MEANGEN-17.3 .

MULTALL-OPEN-17.4 has a few improvements and a few bug fixes but no change to the data input. The most noticeable change is that the smoothing and damping are increased over the first 100 time steps when starting from a restart file. Previously they were not increased at restart. Also the mass flow ratio, which is printed out every 200 steps, is now corrected to allow for shroud leakage flow so even when there is shroud leakage the flow ratio should become closely 1.0 . In throughflow mode the incidence it decreased gradually over the first 1/3 of the grid points on the blade and the deviation is built up over the last 1/2 of the grid points on the blade. The bugs mainly involved the calculation of wall shear stress when there is surface roughness. Also the restart option could not be used when using the SA turbulence model because the turbulent viscosity was not being sent to the restart file.

STAGEN-17.3 allows KTIPS to be set to -1 in the input data file to request data for shrouded blades to be added at the end of the STAGE_NEW.DAT file. However, the data must still be added manually. Also IF_CUSP_OUT can be set in the defaults to decide whether or not to ask MULTALL to generate a cusp. There is no change to the input data.

MEANGEN-17.3 allows FLO_TYPE to be changed from AXI to MIX or vice-versa within a data set, so that part of a machine can be designed as AXI and part as MIX. It also makes an estimate of the mid-span density to give better accuracy in evaluating the annulus area. There are no changes to the data input.

15/8/2017 Add MULTALL-OPEN-17.5

Version 17.5 has a bug fix and several additions. The bug fix is because previous versions did not always allow correctly for the relative motion of the hub or casing in unshrouded blade rows, the end wall was sometimes treated as rotating as the same speed as the blade row. This was correct in subroutine LOSS but wrong in subroutines NEW_LOSS and SPAL_LOSS. It was done correctly in all subroutines in all versions up to MULTALL-15 but somehow got changed in MULTALL-OPEN. Copy the changes from 17.5 if using previous versions of MULTALL_OPEN.

The first addition is to include an option to use the wall functions proposed by Shih et al in NASA/TM-1999-209398. They suggest two terms in the wall function, one based on the velocity near the wall and the other based on the pressure gradient. The velocity term gives very similar results to the existing function in MUTALL It is used by setting YPLUSWALL to any value between -1.0 and -10.0 . The pressure term is new and it is used in combination with the velocity term if YPLUSWALL is set to a

value less than -10.0 . There is as yet little experience of how much difference this makes but so far it seems to have remarkable little effect.

The second addition is to make the changes to the turbulent viscosity source term, ST0, in the Spalart-Allmaras model which were proposed by Lee, Wilson & Vahdati in ASME paper GT2017-63245. They add factors to increase the source term , ST0, when there is streamwise vorticity (helicity) and when there is an adverse pressure gradient and claim that this gives better agreement with predictions of the flow in transonic fans, especially with predictions of the stall point.

The vorticity term is used if the value of FAC_VORT set to be greater than zero. The maximum magnitude of the increase in set equal to FAC_VORT and Lee et al suggest a value of 0.9191 for this.

The pressure gradient term is not so straight-forward since the scaling factor on dimensionless pressure gradient is not given. The original Chinese paper on which the method is based uses a constant scaling factor of 10⁶ , however, this makes the term depend on viscosity, which does not seem realistic. Hence it was decided to multiply the term by the Reynolds number, which gives it a reasonable value and makes it independent of viscosity. The value of the term varies inversely as the sixth power of velocity and so it is concentrated in regions where there is low velocity and an adverse pressure gradient. The term is used if FAC_PGRAD is greater than zero and its maximum magnitude is set equal to FAC_PGRAD. Lee et al suggest a value = 0.6565 for this.

There is little experience of using these options yet but previous experience suggests that the source term in the SA model usually needs to be increased and they certainly seem to extend the operating range of axial compressors before stall. However, use of the pressure gradient term is dubious for centrifugal machines where the “centrifugal force”, which balances the pressure gradient, acts equally on the boundary layer and mainstream.

Both FAC_VORT and FAC_PGRAD are read in at the end of the line of data giving FAC_ST0, etc for the scaling factors on the Spalart-Allmaras terms. The default is that they are both zero.

Two new test cases, 3stg-compr+samods-17.5.dat and r37+samods-17.5.dat, both of which use all the new features, are provided in the “multall-test-cases” folder.

3/10/2017 Add MEANGEN-17.4 and CONVERT-TO-TECPLOT .

MEANGEN-17.4 includes several new features which are described in the MEANGEN-INSTRUCTIONS file. Because of the changes previous MEANGEN.IN data sets are not quite compatible with the new version. Several sample data sets for the new version are proved.

CONVERT-TO-TECPLOT.F is a fortran program which reads in the plotting files “flow_out” and “grid_out” written by MULTALL and converts them to a file “tecplot-input.dat” which can be read by the commercial plotting program TECPLOT. The number of blade passages to be plotted can be chosen and the output is much clearer if two or more passages are used, although the data file can then become quite large.

3/4/2018 . Add MULTALL-OPEN-18.2.f

MULTALL-OPEN-18.2 Has relatively small changes relative to version 14.5. Theres are a few minor bug fixes and a good deal of tidying up. The application of negative feedback and of the limiting Mach number have been improved and the calculation of the one-dimensional mass flow has been made more clear to distinguish between the blade flow and the overall flow. There are no changes to the data input but a sample data set with cooling flows has been added.

18/5/2018 Add MULTALL-OPEN-18.3.f

Version 18.3 . only differs from 18.2 in having a new cooling flow option. This obtains the coolant ejection velocity from the local static pressure and the input value of stagnation pressure. The previous option only allowed the coolant velocity to be set by the input value of coolant ejection Mach number. To use the new option set IFCOOL = 2, to use the original option set IFCOOL = 1. There is no change to the input data. A sample data set for the new option has been added.

There is also a correction to the use of surface roughness if using subroutine NEW_LOSS, and the calculation of mean stage reaction, which was wrong for turbines, has been corrected.

10/01/2020 . Add MULTALL_OPEN-19.2 with an Improved exit boundary condition.

An improved exit boundary condition is available as an option. This is based on a one-dimensional method of characteristics which converts the pitchwise average exit pressure to the specified value by a series of pressure waves. The pitchwise variation of exit pressure is extrapolated from the upstream flow by a fraction FP_XTRAP which is input as data in CARD 23, typical value 0.9 . It is felt that this causes less interference of the downstream boundary with the upstream flow and is particularly desirable when pressure waves are intersecting the downstream boundary.

The new option is used when the new variable FRACWAVE, which is input in CARD 23, is non-zero. If FRACWAVE is not input or is set to 0.0 then the original boundary condition is used. To use the new boundary condition a typical value of FRACWAVE = 0.25 , although lower values can be used if there is any sign of instability. Three new test cases using this option have been added, these are all named . ***-19.2,dat . Previous test cases will run without any modifications and will use the previous exit boundary condition.

Other changes in version 19.2 are correction of a few minor bugs, general tidying up and an option to allow quasi-3D blade to blade calculations to be extended over several blade rows. Previously they could only be used on a single blade row.

29/5/20 . ADD MULTALL-OPEN-20.6. INVERSE BLADE DESIGN MODE

Version 20.6 is the same as 19.2 but with a major addition which allows inverse blade design when operating in the quasi-3D blade-to-blade mode. This allows blades with specified surface pressure distributions to be generated. An inverse calculation is best started from an initial design which can be generated using STAGEN. The initial design sets the number of blades (pitch/chord ratio) and the inlet and exit boundary conditions. A separate file named "inverse.in" giving the desired surface pressure distributions and other control parameters is also read in. The surface pressures of the original blade can then be adjusted to remove any undesirable features such as shock waves and strong adverse pressure gradients and a new blade geometry is generated. The calculation is fully viscous and the stream surface thickness and radius of the stream surface can vary. Run times are of order 2 minutes per run but several runs may be needed to obtain a satisfactory blade.

5/1/2021. MULTALL-OPEN-20.9 . ALLOWS THE USE OF A "LOOKUP TABLE" TO INPUT GAS PROPERTIES FOR ARBITRARY GASES. TABLES ARE PROVIDED FOR STEAM.

The only significant change in version 20.9 is the option to use a "Lookup Table" to input gas properties. The axes of the table are density and internal energy since these are the primary flow quantities calculated by the solver. The properties which must be tabulated as functions of these are : Pressure, Temperature, Entropy, Isentropic index for pressure-density and Dryness Fraction. A short program to obtain these and write the required table using the COOLPROP system of obtaining gas properties is provided. Tables for steam properties are also provided.

More details are in the "updates" file which is included in the download.