i took this one by ozzy https://www.shadertoy.com/view/lsSGWw and tweaked a few things by hand for optimization. saved a few cycles on the code and increased the iterations to 13, which gives a better result.

like this:

#define ITERATIONS 13.0 #define SPEED 10.0 #define DISPLACEMENT 0.05 #define YOFFSET 0.1 #define YSCALE 0.25 #define FLAMETONE vec3(50.0, 5.0, 1.0)

        uniform lowp sampler2D source; // this item
        uniform lowp sampler2D chan0; // random map
        uniform lowp float qt_Opacity; // inherited opacity of this item
        varying highp vec2 qt_TexCoord0;
        uniform highp float    time;           // shader playback time (in seconds)

        float noise( in vec3 x ) // iq noise function
        {
	        vec3 p = floor(x);
            vec3 f = fract(x);
	        f = f*f*(3.0-2.0*f);
	        vec2 uv = (p.xy+vec2(37.0,17.0)*p.z) + f.xy;
	        vec2 rg = texture2D( chan0, (uv + 0.5)/256.0, -100.0 ).yx;
	        return mix( rg.x, rg.y, f.z ) * 2.0 - 1.0;
        }

        void main()
        {
	        vec2 uv = vec2(qt_TexCoord0.s, (1.0 - qt_TexCoord0.t));
	        float nx = 0.0;
	        float ny = 0.0;
            float i;

	        for (i=1.0; i<=ITERATIONS; i = i + 1.0)
	        {
		        float ifrac = i/ITERATIONS;
		        float d = (1.0-ifrac) * DISPLACEMENT;
                ifrac *= time;
		        float ii = i*i;
                float y = uv.y*YSCALE*ii - ifrac * SPEED;
                float x = uv.x*ii;
		        nx += noise( vec3(x-ifrac, y, 0.0)) * d * 2.0;
		        ny += noise( vec3(x+ifrac, y, ifrac/ii)) * d;
	        }

            uv.x += nx;
            uv.y += ny;

            // a blob shape to distort
	        float flame = clamp( sin(uv.x*3.1416) - uv.y+YOFFSET, 0.0, 1.0 );            
            flame *= flame; // f^2
            float ft = flame*flame; // f^4
            flame *= ft*ft; // f^10
            
	        //lowp vec3 col = pow(flame, TIGHTNESS) * FLAMETONE;
	        lowp vec3 col = flame * FLAMETONE;
            
            // tonemapping
            col = col / (1.0+col);
            
            // ~sqrt
            //col = pow(col, vec3(1.0/2.2));
            col = sqrt(col);

            col = clamp(col, 0.0, 1.0);
            
            lowp vec4 p = texture2D(source, qt_TexCoord0);
            p.xyz = col;
            gl_FragColor = p * qt_Opacity;
        }