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A series of laboratory experiments on energy conserving gravity currents in alock-exchange facility are conducted for a range of Reynolds numbers, $Re=\frac{U_Fh}{\nu} =$ 485-12270. The velocity and density fields are capturedsimultaneously using a PIV-PLIF system. A moving average method is employed tocompute the mean field and a host of turbulence statistics, namely, turbulentkinetic energy ($K$), shear production ($P$), buoyancy flux ($B$), and energydissipation ($\epsilon$) during the slumping phase of the current. Thesubsequent findings are used to ascertain the quantitative values of mixingefficiency, $Ri_{f}$, Ozmidov length-scale ($L_O$), Kolmogorov length-scale($L_\kappa$), and eddy diffusivities of momentum ($\kappa_m$) and scalar($\kappa_\rho$). Two different forms of $Ri_{f}$ are characterized in thisstudy, denoted by $Ri_{f}^I=\frac{B}{P}$ and$Ri_{f}^{II}=\frac{B}{B+\epsilon}$. The results cover the entire diffusiveregime (3 $<Re_b<$ 10) and a portion of the intermediate regime (10 $<Re_b<$50), where $Re_b=\frac{\epsilon}{\nu N^2}$ is the buoyancy Reynolds number thatmeasures the level of turbulence in a shear-stratified flow. The values of $P$,$B$, and $\epsilon$ show a marked increase at the interface of the ambientfluid and the current, owing to the development of a shear-driven mixed layer.Based on the changes in the turbulence statistics and the length scales, it isinferred that the turbulence decays along the length of the current. The mixingefficiency monotonically increases in the diffusive regime ($Re_{b}<$10), andis found to have an upper bound of $Ri_{f}^{I}\approx$ 0.15 and$Ri_{f}^{II}\approx$ 0.2 in the intermediate regime. Using the values of$Ri_{f}$, the normalized eddy diffusivity of momentum is parameterized as$\frac{\kappa_m}{\nu.Ri_{g}}$=1.2$Re_{b}$ and normalized eddy diffusivity ofscalar as $\frac{\kappa_{\rho}}{\nu}$=0.2$Re_{b}$

Energetics and mixing efficiency of lock-exchange gravity currents using simultaneous velocity and density fields