## Transient simulation of flow over a throttle body

OBJECTIVE:- STEADY STATE SIMULATION OF FLOW OVER A THROTTLE BODY .

SOFTWARE USED :-

1. CONVERGE STUDIO:- TO SETUP THE MODEL.

2. CYGWIN:- FOR RUNNING THE SIMULATION.

3. OPENFOAM:- TO VISUALIZE THE DIFFERENT POST-PROCESSED RESULT.

THEORY:-

HERE, WE HAVE DONE SIMULATION OF FLOW OVER A THROTTLE BODY IN STEADY STATE .

PRE-PROCESSING STEPS:-

HERE WE HAVE CONSIDER FOLLOWING THINGS FOR ELBOW IN CONVERGE STUDIO:-

(A) TYPE OF FLUID USED:- GAS (MIXTURE OF BASICALLY OXYGEN AND NITROGEN).

(B) TYPE OF CHANNEL:-

IT IS BASICALLY A THROTTLE BODY WHICH IS IN THE SHAPE OF ELBOW .

• OPEN FROM BOTH SIDE OF ELBOW.
• THROTTLE IS WALL .
• BODY IS WALL .

(C).DIMENSION OF CHANNEL:-

1. DIAMETER OF ELBOW =0.0084 m

2. LENGTH OF ELBOW BODY= 0.14 m.

(D).SIZE OF GRID USED:-0.01 FOR LENGTH  AND 0.001 FOR HEIGHT AND BREADTH.

(E). PRESSURE:-

AT INLET, 150000.PASCAL.

AT OUTLET, 100000 PASCAL.

(F). CRITERIA FOR RUNNING SIMULATION :-

1. INTIAL TIME STEP :- 1E-6 SECOND .

2. TIME PERIOD FOR SIMULATION :- 0.01 SECONDS .

3. NUMBER OF CYCLES FOR SIMULATION:- 10000 CYCLES .

(G).  GRID SIZE : - 2 milimeter (FOR ALL DIRECTION i.e LENGTH, BREATH AND HEIGHT) .

HERE , FIXED EMBBEDIING HAVE BEEN USED ON THE THROTTLE BODY.

(H). SOLVER TYPE USED:- PRESSURE BASED (STEADY) .

(I). PRE-PROCESSING STEPS:-

AFTER SETTING UP THE MODEL, WE SENT OUT DATA TO A PARTICULAR LOCATION WHERE ALL THE DETAIL OF CHANNEL IS AVAILABLE REQUIRED BY FURTHER SOFTWARE FOR SIMULATION.

THEN AFTER GENERATING AND STORING THE DATA, WE USED CYGWIN SOFTWARE WHOSE WORK IS TO RUN SIMULATION.

PROCEDURE FOR RUNNING SIMULATION:-

1. OPEN "CYGWIN" IN COMMAND PROMPT.

2. THEN TRACE THE LOCATION WHERE DATA IS STORED FROM CONVERGE STUDIO.

3. NOW TYPE "converge.exe" FOR SERIES SIMULATION OR "mpiexec.exe -n 4 converge" FOR PARALLEL SIMULATION IN THAT FILE LOCATION.

4. AFTER DOING THIS, SIMULATION WILL START WORKING AND AND WILL STOP AFTER GIVEN NUMBER OF CYCLES (BOTH IMPLICITLY AND EXPLICITLY DEPANDING UPON SIMULATION PERIOD).

5. THIS IS HOW THE WORK OF CYGWIN COMPLETES. AFTER THIS USE POST_CONVERT COMMAND IN OUTPUT FILE IS USED WHICH IS GENERATED BY CYGWIN. IT WILL CONVERT THE GENERATED OUT FILE FROM CYGWIN INTO A COMPATIBLE            FROM WHICH WILL BE EASILY ACCESSED BY THE PARAFOAM.

NOW WE OPEN THE PARAFOAM SOFTWARE FOR POST PROCESSING TO VISUALIZE THE RESULT AND COMPARE IT.

POST-PROCESSING STEPS :-

1. IN OPENFOAM, CLICK ON OPEN FROM FILE MENU FROM DROP-DOWN MENU WHICH IS PRESENT AT TOP-LEFT OF THE SCREEN.

2. SEARCH FOR FILE WHERE FILE IS GENERATED BY POST CONVERT COMMAND AND OPEN IT. REMEMBER IT MUST HAVE ".vtm" DOMAIN AFTER FILE NAME.

3. CLICK ON APPLY, GEOMETRY WILL ORIGINATE. AFTER THIS CLICK ON SLICE OPTION TO SECTION THE GEOMETRY . NOW CLICK ON DROP DOWN MENU (SURFACE WITH EDGES) FROM TOP TOOLBAR OPTIONS . THIS WAY THE MESH WILL                    GENERATE .

4. AFTER IT, CLICK ON LINE PROBE OPTION TO SEE THE DIFFERNT PHYSICAL QUANTITES AND APPLY IT.

5. IN THIS WAY, THE GRAPH WILL GENERATE AND WE WILL SEE DIFFERENT PARAMETERS ACCORDING TO THAT APLLIED LINE PLOT.

6. IN THIS WAY, OUR POST-PROCESSING IS DONE.

MESH GENERATED IN TRANSITION STATE :-

CONTOUR PLOT OF PRESSURE  :-

HERE THE PRESSURE CONTOUR HAVE BEEN GENERATED AT THE MID OF THE SIMULATION PERIOD .

HERE ONE MORE THING IS THAT THE MESH REFINEMENT IS DONE MORE FINER AT PORTION OF THE TROTTLE PART .

HERE WE HAVE GENERATED THE PRESSURE CONTOUR PROFILE ACROSS THE ELBOW PIPE . HERE WE OBSERVED THAT PRESSURE IS TOO HIGH AT THE INLET (DEPICTING THE RED PATCHES) OF THROTTLE BODY WHEREAS AT THE OUTLET                (SHOWING THE GREEN PATCH ) BECOMES AVERAGE PRESSURE i.e EQUAL TO THE ATMOSPHERIC PRESSURE .

HERE SOME CELLS ARE MISSING BECAUSE THROTTLE PART IS IN DYNAMIC MOTION. AND SINCE BOTH PRESSURE FLOW AND MESH GENERATION IS INDEPENDENT OF EACH OTHER .THEREFORE IT MAKE'S DIFFICULT FOR PROCESSOR TO CAPTURE    ALL ELEMENTS WITH GRAPHICAL INFORMATION AT SAME PARTICULAR FRAME TIME .

HERE PRESSURE AT THE TROTTLE PART IS CHANGING A LOT BECAUSE OF THE PRESENCE OF TRHOTTLE WHICH TENDS TO RESIST THE INCOMING PRESSURE OF FLUID AS A RESULT OF WHICH PRESSURE CHANGES MUCH .

CONTOUR PLOT OF VELOCITY  :-

HERE SAME THING ARISES IN VELOCITY PROFILE CONTOUR WHICH IS THAT MESH IS NOT TOTALLY GENERATED ACOSS ELBOW PIPE . AGAIN THE REASON IS SAME AS THAT OF PRESSURE CONTOUR .

THE VELOCITY CONTOUR IS ALMOST SAME HERE ALL OVER THE DOMAIN OF ELBOW PIPE SINCE THE SIMULATION HAVE BEEN CAPTURED AT THE MID OF THE TIME OF SIMULATION .

AGAIN AT THROTTLE, VELOCITY IS FACING THE SAME ISSUE i.e IT IS HAVING TURBULENCE  DUE TO THROTTLE WHICH WAS SAME HAPPENING IN PRESSURE CONTOUR .

BUT HERE VELOCITY PROFILE IS SAME AT BOTH ZONES SEPARATED BY THROTTLE . ACTUALLY HERE AS THROTTLE SHIFTS ,THE VELOCITY MAKES ADJUSTMENT PRIOR TO THE SHIFTING OF THROTTLE IN TERMS OF ROTATION HENCE WE SEE THAT     VELOCITY IS SAME AT BOTH ZONES WITH SLIGHT DIFFERENCE .

CONVERGE PLOT OF MASS FLOW RATE  :-

IN THE CONVERGE PLOT OF MASS FLOW RATE , WE OBSERVED THAT MASS FLOW AT INLET AND OUTLET ARE SAME SINCE THE TYPE OF PATH TRACED BY BOTH CURVE ARE IS SAME . HENCE WE CAN CONCLUDE THAT MASS IS CONSERVED OR   PROVING LAW OF CONSERVATION OF MASS .

HERE WHEN THROTTLE IS IN DYNAMIC MOTION BETWEEN 0 TO 2 ms , THE MASS FLOW AT OUTLET VARIES FROM INLET . THE REASON FOR THIS VARIATION IS SUDDEN MOVEMENT OF THROTTLE .

WHEN THROTTLE COMES IN STATIC MOTION BETWEEN 2 TO 4 ms , WHAT WE OBSERVED IS THAT MASS FLOW BECOMES ALMOST SAME AT BOTH ENDS . THE REASON FOR THIS EQUALITY IS THE THROTTLE STEADYNESS IN THIS PERIOD WHICH   PUTS NO EFFECT ON MASS FLOW DUE TO WHICH MASS FLOW BECOMES SAME AT BOTH ENDS .

AFTER 4 ms , WE OBSERVED THAT MASS FLOW IS SAME AT BOTH ENDS INSPITE OF THROTTLE IS IN DYNAMIC MOTION . THIS IS BECAUSE THROTTLE SHIFTNESS IS IN LONG PERIOD WHICH IS ALMOST 8ms . HENCE THIS LONG PERIOD MAKES   VERY SMALL SHIFT IN ROTATION OF THROTTLE DUE TO WHICH WE SAW VERY SMALL VARIATION IN PLOT AT BOTH ENDS  .

NOTE:- HERE SIGN IN CONVERGE PLOT OF CONVERGE STUDIO TELLS US ABOUT THE FLOW OF MASS ACROSS THE DEFINED GEOMETRY OR DOMAIN WHERE IT IS NEGATIVE WHEN IT FLOW INTO THE DOMAIN AND POSITIVE IF IT FLOWS OUT OF   DOMAIN .

CONVERGE PLOT OF PRESSURE  :-

IN THE CONVERGE PLOT OF PRESSURE , WE NOTICED THAT PRESSURE VALUE OF INLET IS CONSTANT THROUGHOUT THE SIMULATION FOR INLET WHEREAS IT VARIES THROUGHOUT THE SIMULATION PERIOD FOR OUTLET . BUT QUESTION ARISES   WHY IS IT SO ? ALTHOUGH WE HAVE PROVIDED THE INTIAL CONDITON FOR BOTH ENDS OF GEOMETRY WHERE IT IS SAME FOR INLET BUT VARIES FOR OUTLET WHEN IT COMES TO SIMULATION .

THE ANSWER OF THIS IS QUITE SIMPLE , WHEN PRESSURE ENTERS THE INLET OF DOMAIN, IT GETS COLLISION WITH INTERNAL PRESSURE OF DOMAIN (THIS INTERNAL PRESSURE ARISES DUE TO PRESENCE OF NITROGEN AND OXYGEN GASES)   DUE TO WHICH THE RESULTING PRESSURE BECOMES DIFFERENT AS WE EXPECT AT OUTLET   HENCE IN THIS WAY THE PRESSURE AT OUTLET VARIES A LOT .

HERE ANOTHER POINT IS THAT WHEN THROTTLE ROTATES , IT CAUSES THE STAGGERNESS IN PRESSURE OVER THE THROTTLE BODY WHICH WE ARE SEEING IN PLOT .

HERE IF WE TAKE THE STATIC PRESSUE CASE PLOT , IT WILL PROVE THIS WHERE IT WILL CHANGE A LOT AT INLET BUT WILL BECOME SAME AT OUTLET OF TOTAL PRESSURE . HERE THE STATIC PRESSURE TELLS THAT HOW MUCH PRESSURE HAVE   BEEN  APPLIED ON THE FLOW OF FLUID . THIS STATIC PRESSURE INTIALLY FACES HIGH RESISTANCE DUE TO INTERNAL PRESSURE  AT INTIAL POINT OF DOMAIN BUT THE RESISTANCE GETS LOWER AS THE FLOW MOVES FORWARD INTO THE   FINAL POINT DOMAIN AND STATIC PRESSURE GETS IT HIGHER VALUE AT OULET WHERE IT HAS NO RESISTANCE.

CONVERGE PLOT OF VELOCITY  :-

IN THE CONVERGE PLOT OF VELOCITY, THE VALUE OF VELOCITY IS SAME AT BOTH INLET AND OULET SECTION . ALTHOUGH THE VELOCITY IS VARYING A LOT THROUGH THE SIMULATION BUT WE OBSERVED THAT BOTH ARE HAVING SAME VARIATION EXPECT THE INTIAL PORTION OF SIMULATION TIME THROUGHOUT THE SIMULATION PERIOD . HENCE WE AGAIN HERE CONCLUDED THAT VELOCITY IS ALSO CONSERVED LIKE MASS FLOW RATE .

HERE BETWEEN THE SIMULATION PERIOD OF 0 TO 2 ms , WE OBSERVE THAT VELOCITY IS VARYING A LOT  I.E DIFFERENT AT BOTH ENDS . THIS IS BECAUSE THE THROTTLE PART IS IN DYNAMIC MOTION WHICH CAUSES THE TROTTLE TO MOVE AT DIFFERENT RATE HENCE THIS REFLECTS BACK IN THE MOTION OF FLUID IN TERMS OF VELOCITY .

BETWEEN 2 ms TO 4 ms , WE OBSERVE THAT NOW VELOCITY AT BOTH SECTION ARE APPROX SAME BECAUSE THE TROTTLE PART COMES IN STATIC MOTION WHICH CAUSES NO DISTURBENCE IN FLOW OF FLUID .

BUT AFTER 4 ms , WE NOTICED THAT INSPITE OF DYNAMIC MOTION OF THROTTLE WE HAVE SAME VELOCITY AT BOTH ENDS . THIS IS BECAUSE THE DYNAMIC MOTION TAKES PLACE IN LONG PERIOD OF 8ms WHICH MAKES THROTTLE TO ADJUST TO IT'S INTIAL POSITION VERY SLOWLY AS A RESULT OF WHICH WE SEE NO SUCH DIFFERENCE IN THIS TIME INTERVAL AT BOTH ENDS COMPARING TO FIRST PERIOD OF DYNAMIC MOTION .

CONVERGE PLOT OF TOTAL CELL COUNT  :-

HERE THE TOTAL CELL COUNT TELLS ABOUT THE NUMBER OF TOTAL GRID POINTS DEFINED FOR DOMAIN OR GEOMETRY . THE CELL COUNTS ARE DIVIDED TO EACH PROCESSOR DEPANDING UPON IT'S PERFORMANCE . HERE THE RANK DENOTES   THE PROCESSOR NUMBER .

HERE WE OBSERVED THAT AT INTIAL PERIOD OF 2 ms , THE THROTTLE WAS IN DYNAMIC MOTION WHICH MAKE THE SUDNENESS IN ELBOW FLOW DUE TO WHICH THE CELL COUNT ALSO VARIED A LOT . HERE AS THROTTLE WAS MOVING   ROTATING FAR AWAY FROM INTIAL POSITION , THE CELL COUNT WAS INCREASING RAPIDLY .

BETWEEN THE PERIOD OF 2ms TO 4 ms , THE CELL COUNT WAS STEADY AND THE REASON FOR THIS STEADYNESS IS THE STATIC POSITION OF THROTTLE WHICH CAUSED NO TURBULENCE IN FLOW DUE TO WHICH NO MUCH CELL GENERATED .

HERE ONE MORE THING WE MAKE CONCLUDE THAT ANY DISTURBENCE IN FLOW OF FLUID DUE TO THROTTLE OR SOMETHING ELSE WILL LEAD TO GENERATION OF MORE CELLS .

ANIMATION OF PRESSURE FLOW ACROSS ELBOW PIPE DURING TRANSITION PERIOD :-

IN ANIMATION OF PRESSURE , WE OBSERVE THAT INTIALLY AT TIME PERIOD OF 2 ms , THE FLUID IN TERMS OF PRESSURE WAS FLOWING WITH FULL PRESSURE . AFTER IT WHEN THROTTLE WAS CHANGING IT'S POSITION TO CLOSE , THE PRESSURE WAS REDUCING SLIGHTLY . THE REASON FOR THIS PHENOMENA IS THE CHANGE OF AREA NEAR THE THROTTLE, WHERE THE FLOW WAS HIGH WHEN THE AREA WAS TOO MUCH BUT SUDDENLY START TO DECLINE VERY MUCH AS THROTTLE SHIFT IT'S POSTION TO CLOSE .

AFTER IT BETWEEEN 2 ms to 4ms , WHEN THROTTLE WAS IN STATIC POSITION . WE OBSERVED THAT THERE WAS NO FLOW ACROSS THE ELBOW . THE REASON BEHIND IT WAS PRESSURE BARRIER WHICH MAKE PRESSURE LIMITED IN ONE ZONE AND ISOLATED IN ANOTHER ZONE .

AFTER 4 ms WHEN THROTTLE OPEN ONCE AGAIN , THE PRESSURE WAS LOWER COMPARING TO INTIAL TIME PERIOD . THIS WAS BECAUSE WHEN THE THROTTLE AGAIN COME IN DYNAMIC MOTION AND TRY TO OPEN . THE PRESSURE BECOME  LOW DUE TO TURBULENCE . HENCE ORIGINAL PRESSURE REDUCES .

ANIMATION OF VELOCITY FLOW ACROSS ELBOW PIPE DURING TRANSITION PERIOD :-

HERE IN VELOCITY PROFILE , VELOCITY IS VERY LOW AT INTIAL PERIOD OF TIME BECAUSE IN THIS TIME PERIOD OF SIMULATION , THE PRESSURE ESTABLISHMENT TAKE PLACE BETWEEN TWO REGIONS DUE TO WHICH VELOCITY BECOMES VERY LOW IN BOTH SECTION ACCORDING TO BERNOUILLE PRINCIPLE .

WITH PASSAGE OF TIME , WHEN THROTTLE COMES IN STATIC POSITION . THE PRESSURE ESTABLISHES IN REGION DUE TO WHICH THE FLOW BECOME CONSISTENT THROUGHOUT THE DOMAIN .

WHEN THROTTLE REOPENS ONCE AGAIN , THE VELOCITY INCREASES IN THE WHOLE REGION . THE REASON BEHIND IS THE PRESSURE BARRIER DUE THROTTLE CLOSENESS AND AS IT OPEN , THE PRESSURE GAP TAKES PLACE WHICH PROVIDE FLOW ADVANTAGE TO MOVE FROM HIGH PRESSURIC TO LOW PRESSURIC REGION . IN THIS WAY THE VELOCITY BECOMES CONSISTENT .

CALCULATION OF END TIME OF SIMULATION :-

TOTAL LENGTH OF THROTTLE BODY = 0.14 m .

AVERAGE VELOCITY OF FLUID AT THE INLET OF THROTTLE BODY = 80 m/s.

HENCE , END TIME PERIOD FOR SIMULATION WILL BE = ( TOTAL LENGTH OF THROTTLE BODY) / (AVERAGE VELOCITY AT INLET) = (0.14/80)= 0.0018 approximately .

NOTE :- HERE WE TAKEN END TIME FOR SIMULATION AS 0.01 SECONDS . THE REASON FOR IT IS THAT WE WANT TO SAVE THE RESTART FILE SO THAT WE CAN SAVE SIMULATION DATA AND AVOID LOSING OF DATA DURING CRASHING  . HERE RESTART TIME IS TAKEN AS 0.0001 SECONDS DUE TO WHICH WE HAVE CONSIDERED SIMULATION PERIOD AS 0.01 SECONDS . HENCE WE HAVE 100 RESTART FILES AND MORE PRECISE INFORMATION .

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