**RSICC CODE PACKAGE PSR-437**

**1. NAME AND TITLE**

ORSMAC: Code System to Calculate Fluid Circulation Patterns Near Jets.

**2. CONTRIBUTORS**

Oak Ridge Gaseous Diffusion Plant, Tennessee, through the Energy Science and Technology Software Center, Oak Ridge, Tennessee.

**3. CODING LANGUAGE AND COMPUTER**

Fortran (91%) and BAL (9%); IBM3033 (P00437IBM303300).

**4. NATURE OF PROBLEM SOLVED**

ORSMAC predicts the temperatures occurring in the immediate vicinity (the near field) of a hot water discharge from a power plant. ORSMAC numerically solves the differential equations governing the conservation of mass, momentum, and energy in a two-dimensional vertical plane containing the power plant discharge. The model allows arbitrary discharge angle and can accommodate either quiescent or cross-flowing ambient conditions.

**5. METHOD OF SOLUTION**

The ORSMAC technique is an extension of the Simplified Marker And Cell (SMAC) algorithm for calculating transient flows of a laminar, incompressible fluid in the presence of a free surface. In ORSMAC, the logic for simple turbulence modeling, energy conservation, and buoyancy effects is added to the classic MAC technique. Extensions include: generating the Poisson equation for the pressure corrections as a matrix with built-in boundary conditions; counting particle movements from full cells to empty cells in a single time-step and then automatically recalculating the maximum stable time-step allowed; writing a printer-plot routine which produces stream function contours (to show flow direction) and isotherms (to show distribution of hot water) at arbitrary times; modifying boundary conditions for the bottom of the mesh to allow fluid to flow out of the mesh (an ''intake'' for a power plant) and to be discharged into the mesh at a specified velocity, temperature, and direction; adding an automatic procedure for adjusting the time-step to maintain numerical stability; integrating a simple scalar (mixing length) turbulence model based on a time and space-varying eddy viscosity concept using finite difference estimates for convective transport that stabilize the momentum and energy equations; formulating the energy transport equation to handle free surface conditions correctly; implementing an alternate treatment for the liquid free surface based on the SOLA-SURF algorithm and an alternating-direction, relaxation-by-lines algorithm to solve the generalized Poisson equation for each time-step.

**6. RESTRICTIONS OR LIMITATIONS**

The proper choice of boundary condition options must be made for each physical situation, and the selection of initial conditions for steady-state problems can influence the cost of the solution.

**7. TYPICAL RUNNING TIME**

Approximately 1 hour of CPU time would be necessary for the sample problem to converge on an IBM3033.

**8. COMPUTER HARDWARE REQUIREMENTS**

The code ran on IBM 3033 and IBM 4331 mainframe computers.

**9. COMPUTER SOFTWARE REQUIREMENTS**

ORSMAC ran on MVS (IBM3033) and VM/CMS (IBM4331). The files have not been modified since they were tested and initially released by NESC in 1989. The package was transferred to ESTSC then to RSICC and rereleased in January 2002.

**10. REFERENCES**

** a) Included in documentation:**

J.E. Park and K.E. Cross, "Calculation of Fluid Circulation Patterns in the Vicinity of Submerged Jets Using ORSMAC," NUREG/CR-3153 (ORNL/TM-8653) (December 1983).

** b) Background reference:**

A.A. Amsden and F.H. Harlow, "The SMAC Method: A Numerical Technique for Calculating Incompressible Fluid Flows," LA-4370 (May 1970).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced document in 10.a and a DS/HD diskette which includes the ORSMAC source files and test case input and output transmitted as DOS files.

**12. DATE OF ABSTRACT**

January 2002.

** KEYWORDS:** FLUID DYNAMICS; HYDRODYNAMICS; THERMAL HYDRAULICS