problem with triangulation matlab

Hello, my friends; I am trying to interpret Fluent data for a wavy tunnel. The issue lies in the triangulation, as shown in the image. I am unsure how to resolve it and do not understand how to prevent the triangulation from occurring.

% Let the user choose the folder containing the text files
folder_path = uigetdir('Select the folder containing the text files');

% Check if the user canceled folder selection
if folder_path == 0
    disp('Folder selection canceled. Exiting...');
    return;
end

% Get a list of all the text files in the folder
file_list = dir(fullfile(folder_path, '*.txt'));

% Initialize cell arrays to store data for each variable
x_cell = cell(length(file_list), 1);
y_cell = cell(length(file_list), 1);
u_cell = cell(length(file_list), 1);
v_cell = cell(length(file_list), 1);
T_cell = cell(length(file_list), 1);
P_cell = cell(length(file_list), 1);
Tw_cell = cell(length(file_list), 1);
% rho_cell = cell(length(file_list), 1);
% k_cell = cell(length(file_list), 1);
% dissRate_cell = cell(length(file_list), 1);
% Visxosity_cell = cell(length(file_list), 1);
% Cp_cell = cell(length(file_list), 1);
% thermal_cell = cell(length(file_list), 1);

% Loop through each file and read its contents
for i = 1:length(file_list)
    % Get the file name
    file_name = fullfile(folder_path, file_list(i).name);
    
    % Read the data from the file
    data = readtable(file_name);
    
    % Store the data in the cell arrays with the file name as the cell name
    [~, file_name_only, ~] = fileparts(file_name);
    x_cell{i} = struct('file_name', file_name_only, 'data', data.x_coordinate);
    y_cell{i} = struct('file_name', file_name_only, 'data', data.y_coordinate);
    u_cell{i} = struct('file_name', file_name_only, 'data', data.x_velocity);
    v_cell{i} = struct('file_name', file_name_only, 'data', data.y_velocity);
    T_cell{i} = struct('file_name', file_name_only, 'data', data.temperature);
    P_cell{i} = struct('file_name', file_name_only, 'data', data.pressure);
    Tw_cell{i} = struct('file_name', file_name_only, 'data', data.wall_temperature);
    % rho_cell{i} = struct('file_name', file_name_only, 'data', data.density);
    % k_cell{i} = struct('file_name', file_name_only, 'data', data.turb_kinetic_energy);
    % dissRate_cell{i} = struct('file_name', file_name_only, 'data', data.turb_diss_rate);
    % Visxosity_cell{i} = struct('file_name', file_name_only, 'data', data.viscosity_lam);
    % Cp_cell{i} = struct('file_name', file_name_only, 'data', data.specific_heat_cp);
    % thermal_cell{i} = struct('file_name', file_name_only, 'data', data.thermal_conductivity_lam);
end
%%
% Initialize structures to store wall coordinates and number of y coordinates
wall_coords_down = struct('x', {}, 'y', {});
wall_coords_yp = struct('x', {}, 'y', {});
num_y_coordinates = struct('file_name', {}, 'num_y', {});
y_coordinates_end_tunnel = struct('file_name', {}, 'num_y', {});

for i = 1:length(file_list)
    % Find wall coordinates
    xwall = x_cell{i}.data(Tw_cell{i}.data > 0);
    ywall = y_cell{i}.data(Tw_cell{i}.data > 0);

    % Find the largest wall X-coordinate (end of the tunnel)
    largest_wall_X = max(xwall);

    % Find the index of the largest wall X-coordinate
    largest_wall_X_idx = find(xwall,1, 'last');   
   

        % Determine the distance between the largest wall X-coordinate and the preceding one
        distance_between = max(gradient(sort(xwall)));

        % Define the search range for X-coordinates
        EndOfTunnel = find(largest_wall_X - 0.7 * distance_between < x_cell{i}.data & x_cell{i}.data <= largest_wall_X);

        % Extract the corresponding y-coordinates
        y_coordinates_end_tunnel(i).file_name = x_cell{i}.file_name;
        y_coordinates_end_tunnel(i).num_y = y_cell{i}.data(EndOfTunnel);

        % Store wall coordinates
        wall_coords_up(i).x = xwall(ywall>(max(ywall)+min(ywall))/2);
        wall_coords_up(i).y = ywall(ywall>(max(ywall)+min(ywall))/2);
        wall_coords_down(i).x = xwall(ywall<(max(ywall)+min(ywall))/2);
        wall_coords_down(i).y = ywall(ywall<(max(ywall)+min(ywall))/2);

        % Count the number of y-coordinates
        num_y_coordinates(i).file_name = x_cell{i}.file_name;
        num_y_coordinates(i).num_y = length(y_coordinates_end_tunnel(i).num_y);
    
end

%%
% Initialize structures to store interpolated data
interp_u_cell = cell(length(file_list), 1);
interp_v_cell = cell(length(file_list), 1);
interp_T_cell = cell(length(file_list), 1);
interp_P_cell = cell(length(file_list), 1);
interp_Tw_cell = cell(length(file_list), 1);
interp_x_cell = cell(length(file_list), 1);
interp_y_cell = cell(length(file_list), 1);

for i = 1:length(file_list)
    % Find wall coordinates
    xwall = x_cell{i}.data(Tw_cell{i}.data > 0);
    ywall = y_cell{i}.data(Tw_cell{i}.data > 0);
    
    
    % Find the largest wall X-coordinate (end of the tunnel)
    largest_wall_X = max(xwall);

    % Calculate the distance between the maximum and minimum wall X-coordinates
    distance_total = max(xwall) - min(xwall);
    
    % Define the wavelength
    wavelength = 28.8/1000;  % m

    % Calculate the number of sections based on the wavelength
    num_sections = floor(distance_total / wavelength);

    % Initialize structures to store interpolated data for each section
    interp_u = cell(num_sections, 1);
    interp_v = cell(num_sections, 1);
    interp_T = cell(num_sections, 1);
    interp_P = cell(num_sections, 1);
    interp_Tw = cell(num_sections, 1);
    interp_x= cell(num_sections, 1);
    interp_y = cell(num_sections, 1);
    interp_x_new= cell(num_sections, 1);
    interp_y_new = cell(num_sections, 1);

    % Initialize starting point for creating sections
    current_x = largest_wall_X;

    % Loop to create sections and interpolate data within each section
    for j = 1:num_sections
        % Find the end point of the current section
        end_x = current_x - wavelength;
        disp(end_x);disp(current_x);disp(wavelength);
        % Find the indices of x coordinates within the current section
        section_indices = find(x_cell{i}.data >= end_x-0.0001 & x_cell{i}.data <= current_x);
        wall_length = length(xwall(xwall >= end_x & xwall <= current_x));
        
         % Extract the x and y coordinates within the current section
        section_x = x_cell{i}.data(section_indices);
        disp(min(section_x));disp(max(section_x));
        section_y = y_cell{i}.data(section_indices);
        section_u = u_cell{i}.data(section_indices);
        section_v = v_cell{i}.data(section_indices);
        section_T = T_cell{i}.data(section_indices);
        section_P = P_cell{i}.data(section_indices);
        section_Tw = Tw_cell{i}.data(section_indices);
        
      
        % Create linearly spaced vectors for interpolation
        % interp_X = linspace(min(section_x), max(section_x), wall_length * 5);
        % interp_Y = linspace(min(section_y), max(section_y), num_y_coordinates(i).num_y * 3);
        % [interp_X_grid, interp_Y_grid] = meshgrid(interp_X, interp_Y);
        Ylength = num_y_coordinates(i).num_y*3.5;
        Ylength = 200;

        interp_X = linspace(min(section_x), max(section_x), round(Ylength)*round(1.694444444));
        interp_Y = linspace(min(section_y), max(section_y),round(Ylength));

        % Construct meshgrid
        [interp_x{j}, interp_y{j}] = meshgrid(interp_X, interp_Y);
                
            F_u = scatteredInterpolant(section_x, section_y, section_u, 'natural', 'none');
            % F_v = scatteredInterpolant(section_x, section_y, suection_v, 'natural', 'none');
            % F_T = scatteredInterpolant(section_x, section_y, section_T, 'natural', 'none');
            % F_P = scatteredInterpolant(section_x, section_y, section_P, 'natural', 'none');
            % 
            % 
            % % Interpolate and re-normalize the data
            % 
            interp_u{num_sections- j + 1} = smooth2a(F_u(interp_x{j}, interp_y{j}),8,8);
            % interp_v{num_sections- j + 1} = smooth2a(F_v(interp_x{j}, interp_y{j}),8,8);
            % interp_T{num_sections- j + 1} = smooth2a(F_T(interp_x{j}, interp_y{j}),8,8);
            % interp_P{num_sections- j + 1} = smooth2a(F_P(interp_x{j}, interp_y{j}),8,8);
             interp_x_new{num_sections- j + 1} = interp_x{j};
             interp_y_new{num_sections- j + 1} = interp_y{j};
            
            % Update current_x for the next section
        current_x = end_x;
    end

 
% Update cell arrays to contain the combined matrices
interp_u_cell{i} = struct('file_name', x_cell{i}.file_name, 'data', interp_u);
interp_v_cell{i} = struct('file_name', x_cell{i}.file_name, 'data', interp_v);
interp_T_cell{i} = struct('file_name', x_cell{i}.file_name, 'data', interp_T);
interp_P_cell{i} = struct('file_name', x_cell{i}.file_name, 'data', interp_P);
interp_x_cell{i} = struct('file_name', x_cell{i}.file_name, 'data', interp_x_new);
interp_y_cell{i} = struct('file_name', x_cell{i}.file_name, 'data', interp_y_new);
end

folder_path = uigetdir('Select the folder containing the text files');
% Define the file name without leading space characters
% Define the file name without leading space characters
filename = 'StaedyFlowM028Re8000.mat';

% Concatenate the folder path and file name to create the full path
full_path = fullfile(folder_path, filename);

% Save the structures to the file using MAT-file version 7.3
save(full_path, 'interp_u_cell', 'interp_v_cell', 'interp_T_cell', 'interp_P_cell', 'interp_Tw_cell', 'interp_x_cell', 'interp_y_cell', '-v7.3');

[Swastik Sarkar]

Hi @ran,

Could you please specify how we can use the file you have attached to plot the figure ?