// ======== Global Parameters ======== //
$fn = 75;
inlet_segments      = 60;
outlet_segments     = 20;

// ======== Venturi Geometry ======== //
inlet_length        = 250;
outlet_length       = 350;
inlet_radius        = 200;
throat_radius       = 80;
outlet_radius       = 110;
wall_thickness      = 5;

inlet_curve_factor  = 2;
outlet_curve_factor = 1.5;

// ======== Utility Module ======== //
module stacked_shell(length, r_end, thickness, segments, curve_factor, is_outer = true) {
    for (i = [0:segments - 1]) {
        h = length / segments;
        t0 = i / (segments - 1);
        t1 = (i + 1) / (segments - 1);

        r1 = throat_radius + (r_end - throat_radius) * pow(t0, curve_factor);
        r2 = throat_radius + (r_end - throat_radius) * pow(t1, curve_factor);

        if (!is_outer) {
            r1 = r1 - thickness;
            r2 = r2 - thickness;
        }

        translate([0, 0, i * h])
            cylinder(h = h, r1 = r1, r2 = r2);
    }
}

// ======== Inlet Module ======== //
module inlet() {
    difference() {
        stacked_shell(inlet_length, inlet_radius, wall_thickness, inlet_segments, inlet_curve_factor, true);
        stacked_shell(inlet_length, inlet_radius, wall_thickness, inlet_segments, inlet_curve_factor, false);
    }
}

// ======== Outlet Module ======== //
module outlet() {
    difference() {
        stacked_shell(outlet_length, outlet_radius, wall_thickness, outlet_segments, outlet_curve_factor, true);
        stacked_shell(outlet_length, outlet_radius, wall_thickness, outlet_segments, outlet_curve_factor, false);
    }
}

// ======== Top-Level Geometry ======== //
translate([0, 0, 0])
    rotate([0, -90, 0]) inlet();

translate([0, 0, 0])
    rotate([0, 90, 0]) outlet();