  We conduct experiments in a turbulent bubbly flow to study the nature of the
transition between the classical $-$5/3 energy spectrum scaling for a
single-phase turbulent flow and the $-$3 scaling for a swarm of bubbles rising
in a quiescent liquid and of bubble-dominated turbulence. The bubblance
parameter, which measures the ratio of the bubble-induced kinetic energy to the
kinetic energy induced by the turbulent liquid fluctuations before bubble
injection, is often used to characterise the bubbly flow. We vary the bubblance
parameter from $b = \infty$ (pseudo-turbulence) to $b = 0$ (single-phase flow)
over 2-3 orders of magnitude ($0.01 - 5$) to study its effect on the turbulent
energy spectrum and liquid velocity fluctuations. The probability density
functions (PDFs) of the liquid velocity fluctuations show deviations from the
Gaussian profile for $b > 0$, i.e. when bubbles are present in the system. The
PDFs are asymmetric with higher probability in the positive tails. The energy
spectra are found to follow the $-$3 scaling at length scales smaller than the
size of the bubbles for bubbly flows. This $-$3 spectrum scaling holds not only
in the well-established case of pseudo-turbulence, but surprisingly in all
cases where bubbles are present in the system ($b > 0$). Therefore, it is a
generic feature of turbulent bubbly flows, and the bubblance parameter is
probably not a suitable parameter to characterise the energy spectrum in bubbly
turbulent flows. The physical reason is that the energy input by the bubbles
passes over only to higher wave numbers, and the energy production due to the
bubbles can be directly balanced by the viscous dissipation in the bubble wakes
as suggested by Lance $\&$ Bataille (1991). In addition, we provide an
alternative explanation by balancing the energy production of the bubbles with
viscous dissipation in the Fourier space.
