Flush file without closing it

Program.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp {
    class Program {
        static void Main(string[] args) {

            using (var sw = new StreamWriter(File.Open("log.txt", FileMode.Append, FileAccess.Write, FileShare.Read))) {
                string cmd = null;

                while (cmd != "q") {

                    sw.WriteLine(DateTime.Now.ToLongTimeString());
                    sw.Flush();

                    cmd = Console.ReadLine();

                }
            }

        }
    }
}