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#include <iostream>
#include <vector>
#include <algorithm>
#include "lbm.h"
#include "boundary_conditions.h"
constexpr std::size_t dimY = 20;
constexpr std::size_t dimX = 5*dimY;
constexpr double uInflow = 0.02;
constexpr double reynolds = 100;
constexpr double tau = 3. * uInflow * (dimX-1) / reynolds + 0.5;
constexpr double omega = 1. / tau;
DataCellBuffer pop(dimX, dimY);
FluidBuffer fluid(dimX, dimY);
double poiseuille(std::size_t y) {
return -4. * uInflow / (dimY*dimY) * (y+0.5) * (y+0.5 - dimY);
}
void init() {
for ( std::size_t x = 0; x < dimX; ++x ) {
for ( std::size_t y = 0; y < dimY; ++y ) {
fluid.density(x,y) = 1.0;
fluid.velocity(x,y) = {0.0, 0.0};
static_cast<Cell&>(pop.curr(x,y)).equilibrize(
fluid.density(x,y), fluid.velocity(x,y));
static_cast<Cell&>(pop.prev(x,y)).equilibrize(
fluid.density(x,y), fluid.velocity(x,y));
}
}
}
void computeLbmStep() {
pop.swap();
for ( std::size_t x = 0; x < dimX; ++x ) {
for ( std::size_t y = 0; y < dimY; ++y ) {
streamFluidCell(pop, x, y);
}
}
for ( std::size_t x = 0; x < dimX; ++x ) {
computeWallCell(pop, {x, 0 }, { 0, 1});
computeWallCell(pop, {x, dimY-1}, { 0,-1});
}
for ( std::size_t y = 1; y < dimY-1; ++y ) {
computeMovingWallCell(pop, {0,y}, {1,0}, {poiseuille(y), 0});
}
for ( std::size_t x = 0; x < dimX; ++x ) {
for ( std::size_t y = 0; y < dimY; ++y ) {
Cell& cell = static_cast<Cell&>(pop.curr(x,y));
// bulk density
fluid.density(x,y) = cell.sum();
// outflow density condition
if ( x == dimX-1 && y > 0 && y < dimY-1 ) {
fluid.density(x,y) = 1.0;
}
fluid.velocity(x,y) = cell.velocity(fluid.density(x,y));
collideFluidCell(omega, pop, fluid, x, y);
}
}
}
double error(std::size_t x) {
double acc = 0.0;
for ( std::size_t y = 1; y < dimY-1; ++y ) {
acc += std::abs(poiseuille(y) - fluid.velocity(x,y)[0]);
}
return acc / (dimY-2);
}
int main() {
init();
std::cout << "dim: " << dimX << "x" << dimY << std::endl;
std::cout << "Re: " << reynolds << std::endl;
std::cout << "uInflow: " << uInflow << std::endl;
std::cout << "tau: " << tau << std::endl;
std::cout << "omega: " << omega << std::endl;
std::cout << std::endl;
for ( std::size_t t = 0; t <= 10000; ++t ) {
computeLbmStep();
if ( t % 1000 == 0 ) {
std::cout << error(dimX-1) << std::endl;
fluid.writeAsVTK("result/poiseuille_t" + std::to_string(t) + ".vtk");
}
}
}
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