I have a set of PDEs & I tried to solve it. First of all I defined some functions as:

H := (diff(a(t, y), t))/a(t, y), Hy := (diff(a(t, y), y))/a(t, y), H1 := diff(H(t, y), t), a1 := diff(a(t, y), t), a2 := diff(a1, t), Hy1 := diff(Hy(t, y), y), ay1 := diff(a(t, y), y), ay2 := diff(ay1, y), n1 := diff(n(t, y), t), n2 := diff(n1, t), ny1 := diff(n(t, y), y), ny2 := diff(ny1, y), pef := -2*n(t, y)^2*Hy1-3*n(t, y)^2*Hy^2-n(t, y)*ny2-2*n(t, y)*Hy*ny1-2*H(t, y)*n1/n(t, y), `ρef` := 3*n(t, y)^2*Hy1+6*n(t, y)^2*Hy^2, `ωef` := pef/`ρef`,