# Some measurements in a binary gas jet

- Received:

DOI: 10.1007/BF00233128

- Cite this article as:
- So, R.M.C., Zhu, J.Y., Ötügen, M.V. et al. Experiments in Fluids (1990) 9: 273. doi:10.1007/BF00233128

- 36 Citations
- 111 Downloads

## Abstract

Simultaneous measurements of species volume concentration and velocities in a helium/air binary gas jet with a jet Reynolds number of 4,300 and a jet-to-ambient fluid density ratio of 0.64 were carried out using a laser/hot-wire technique. From the measurements, the turbulent axial and radial mass fluxes were evaluated together with the means, variances and spatial gradients of the mixture density and velocity. In the jet near field (up to ten diameters downstream of the jet exit), detailed measurements of *ϱ′ u′/ϱ*_{0}*U*_{0}, *ϱ′ v′/ϱ*_{0} U_{0}, *ϱ u′ v′/ϱ*_{0}*U*_{0}^{2}, *ϱ′u′*^{2}*/ϱ*_{0}*U*_{0}^{2} and *ϱ′ v′*^{2}*/ϱ*_{0}*U*_{0}^{2} reveal that the first three terms are of the same order of magnitude, while the last two are at least one order of magnitude smaller than the first three. Therefore, the binary gas jet in the near field cannot be approximated by a set of Reynolds-averaged boundary-layer equations. Both the mean and turbulent velocity and density fields achieve self-preservation around 24 diameters. Jet growth and centerline decay measurements are consistent with existing data on binary gas jets and the growth rate of the velocity field is slightly slower than that of the scalar field. Finally, the turbulent axial mass flux is found to follow gradient diffusion relation near the center of the jet, but the relation is not valid in other regions where the flow is intermittent.

### List of symbols

*a*_{u},*a*_{ϱ},*a*_{θ},*a*_{c}constants in hyperbolic decay laws

*c*instantaneous helium volume concentration

*c*′fluctuating part of

*c**C*mean of

*c**d*_{ɛ}effective jet diameter,

*σ*_{1}^{1/2}*D**D*jet nozzle diameter

*D*_{Tu}turbulent diffusivity along

*x**D*_{Tv}turbulent diffusivity along

*r**k*_{u},*k*_{ϱ},*k*_{θ},*k*_{c}hyperbolic decay constants for

*u, ϱ, θ*and*c*, respectively*N*number of samples in each data record

*P*mean static pressure

*r*radial coordinate measured from jet centerline

*Re*jet Reynolds number,

*U*_{j}*D/v*_{j}*u*_{i}instantaneous

*i*^{th}component of velocity*u*_{i}*′*fluctuating part of

*u*_{i}*u*_{i}*″*fluctuating part of Favre decomposition of

*u*_{i}*Ū*_{i}mean of

*u*_{i}*Ũ*_{i}Favre-averaged of

*u*_{i}*u*instantaneous axial velocity

*u′*fluctuating part of

*u**u″*fluctuating part of Favre decomposition of

*u**Ū*mean of

*u**Ũ*Favre-averaged of

*u**v*instantaneous radial velocity

*v′*fluctuating part of

*v**v″*fluctuating part of Favre decomposition of

*v**V*mean of

*v*- \(\tilde V\)
Favre-averaged of

*v**x*axial coordinate measured from jet nozzle exit

*x*_{i}*i*^{th}component of coordinates*x*_{0}virtual origin of jet

### Greek symbols

- α
density ratio parameter, (

*ϱ*_{h}/*ϱ*_{a}-1)*δ*_{c}jet half width based on

*C*profile*δ*_{u}jet half width based on

*Ū*profile*δ*_{u}∼jet width based on

*Ū/Ū*_{0}= 0.75*δ*_{θ}jet half width based on \(\bar \theta\) profile

*η*dimensionless

*r*-coordinate,*r/δ*_{u}*η*_{θ}dimensionless

*r*-coordinate,*r/δ*_{θ}*θ*instantaneous mixture mass fraction or temperature

*θτ*fluctuating part of

*θ*- \(\bar \theta\)
mean of

*θ**ϱ*instantaneous mixture density

*ϱτ*fluctuating part of

*ϱ*- \(\bar \rho\)
mean of

*ϱ**σ*_{1}density ratio of jet,

*θ*_{j}/*θ*_{a}*μ*_{T}turbulent viscosity

*ν*fluid kinematic viscosity

### Subscripts

*a*air

*h*helium

*j*jet

*o*centerline values

### Overscores

- -
time-averaged value

- ∼
Favre-averaged value