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{{ACHeader
{{ACHeader_ref
|area=3
|area=3
|number=12
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such a complex swirling flow, detailed experiments  were  conducted  on
such a complex swirling flow, detailed experiments  were  conducted  on
particle-laden  swirling  flow  emanating  into  a  pipe  expansion
particle-laden  swirling  flow  emanating  into  a  pipe  expansion
(Sommerfeld and  Qiu  1991).  The  gas-particle  mixture  was  injected
([[References_AC3-12#8|Sommerfeld and  Qiu  1991]]).  The  gas-particle  mixture  was  injected
centrally without swirl together with a co-flowing swirling annular gas
centrally without swirl together with a co-flowing swirling annular gas
jet yielding a swirl number of  about  0.5.  Downstream  of  the  inlet
jet yielding a swirl number of  about  0.5.  Downstream  of  the  inlet
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identical swirl number were considered.  Both  cases  showed  a  closed
identical swirl number were considered.  Both  cases  showed  a  closed
central recirculation  region.  Inlet  conditions  are  available  from
central recirculation  region.  Inlet  conditions  are  available  from
highly resolved profiles 3 mm downstream of  the  edge  of  the  inflow
highly resolved profiles 3 mm downstream of  the  edge  of  the  inflow
tubes. Since the particle mass loading is rather small two-way coupling
tubes. Since the particle mass loading is rather small two-way coupling
effects are of minor importance. Numerical computations performed  with
effects are of minor importance. Numerical computations performed  with
the finite-volume code FASTEST in connection with  the  k-ε  turbulence
the finite-volume code FASTEST in connection with  the  k-ε  turbulence
model  showed  reasonable  good  agreement  with  the  measurements
model  showed  reasonable  good  agreement  with  the  measurements
(Sommerfeld  and  Qiu  1993).  The  particle  phase  was  simulated  by
([[References_AC3-12#11|Sommerfeld  and  Qiu  1993]]).  The  particle  phase  was  simulated  by
Lagrangian tracking also yielding a quite good agreement with  measured
Lagrangian tracking also yielding a quite good agreement with  measured
velocity profiles, the particle mass flux and the number mean  particle
velocity profiles, the particle mass flux and the number mean  particle
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==Flow Domain Geometry==  
==Flow Domain Geometry==  
<!--{{Demo_AC_Desc_Geom}}-->
The swirling flow was realized in a kind of pipe expansion flow
The swirling flow was realized in a kind of pipe expansion flow
([[Description_AC3-12#figure1|Figure 1]]).
([[Description_AC3-12#figure1|Figure 1]]).


Through the central inlet tube (diameter 32 mm)  the  gas-particle
Through the central inlet tube (diameter 32&nbsp;mm)  the  gas-particle
mixture was injected into the  test  section  without  swirl.  The  co-
mixture was injected into the  test  section  without  swirl.  The  co-
flowing swirling flow was produced by a  vane-swirl  generator  located
flowing swirling flow was produced by a  vane-swirl  generator  located
upstream the inlet. The annular inlet tube has an inner diameter of  38
upstream the inlet. The annular inlet tube has an inner diameter of  38&nbsp;mm
mm and an outer diameter of 64 mm. The test section has a  diameter  of
and an outer diameter of 64&nbsp;mm. The test section has a  diameter  of
194 mm and a length of 1,500 mm.  The  end  of  the  test  section  is
194&nbsp;mm and a length of 1,500&nbsp;mm.  The  end  of  the  test  section  is
connected to a sufficiently wide stagnation chamber.
connected to a sufficiently wide stagnation chamber.


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The considered swirling flow is highly turbulent, but may be considered
The considered swirling flow is highly turbulent, but may be considered
as incompressible. The measurements were done under ambient  conditions
as incompressible. The measurements were done under ambient  conditions
with a temperature of about 300 K yielding an air density of 1.18 kg/m<sup>3</sup>
with a temperature of about 300&nbsp;K yielding an air density of 1.18&nbsp;kg/m<sup>3</sup>
and a dynamic viscosity of 18.4&times;10<sup>-6</sup> kg/(m·s). The characteristic  non-
and a dynamic viscosity of 18.4&times;10<sup>-6</sup>&nbsp;kg/(m·s). The characteristic  non-
dimensional parameters are:
dimensional parameters are:


The flow Reynolds number which is calculated with the total volume flow
 
The flow Reynolds number, which is calculated with the total volume flow
rate, the outer diameter of the annulus and the effective inlet  cross-
rate, the outer diameter of the annulus and the effective inlet  cross-
sectional area A<sub>in</sub>:
sectional area A<sub>in</sub>:
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<center><math>{Re=\frac{\rho D_3\dot{Q}}{\mu A_\text{in}}}</math></center>
<center><math>{Re=\frac{\rho D_3\dot{Q}}{\mu A_\text{in}}}</math></center>


The swirl number which is the  ratio  of  the  axial  flux  of  annular
The swirl number, which is the  ratio  of  the  axial  flux  of  annular
momentum to the axial flux of linear momentum obtained  by  integration
momentum to the axial flux of linear momentum obtained  by  integration
across the primary and annular inlets:
across the primary and annular inlets:


<center><math>{S=\frac{2\int_0^{D_3/2}\rho W U r^2\ dr}{D_5\int_0^{D_3/2}\rho U^2 r\ dr}}</math></center>
<center><math>{S=\frac{\displaystyle 2\int_0^{D_3/2}\rho\ W U r^2\ dr}{\displaystyle D_5\int_0^{D_3/2}\rho\ U^2 r\ dr}}</math></center>




Here ''U'' and ''W'' are the mean axial and tangential velocities and ''r'' is  the
Here ''U'' and ''W'' are the mean axial and tangential velocities and ''r'' is  the
radius. The values of the outer diameter of  the  inlet,  ''D<sub>3</sub>'',  and  the
radius. The values of the outer diameter of  the  inlet,  ''D<sub>3</sub>'',  and  the
inner diameter of the test section ''D<sub>5</sub>'' are given in Fig. 1. The Reynolds
inner diameter of the test section ''D<sub>5</sub>'' are given in
[[Description_AC3-12#figure1|Figure&nbsp;1]]. The Reynolds
numbers of the two cases considered are 52400 and 54500 and  the  swirl
numbers of the two cases considered are 52400 and 54500 and  the  swirl
numbers are around 0.5.
numbers are around 0.5.
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As mentioned above, the particle mass loading was rather  low  so  that
As mentioned above, the particle mass loading was rather  low  so  that
the effect of the particles on the flow field  may  be  neglected.  The
the effect of the particles on the flow field  may  be  neglected.  The
particles are spherical glass beads with a material  density  of  2,500
particles are spherical glass beads with a material  density  of  2,500&nbsp;kg/m<sup>3</sup>
kg/m<sup>3</sup> and a relative wide size distribution ranging between about 10 µm
and a relative wide size distribution ranging between about 10&nbsp;µm
to 80 µm. The number mean diameter (mean  diameter  based  on  particle
to 80&nbsp;µm. The number mean diameter (mean  diameter  based  on  particle
counts) is 45 µm yielding a mean Stokesian response time  of  about  15 ms.
counts) is 45&nbsp;µm yielding a mean Stokesian response time  of  about  15&nbsp;ms.


<center><math>{St=\frac{\rho_p \bar{D_p}^2}{18\mu}}</math></center>
<center><math>{\tau_p=\frac{\rho_p \overline{D}_p^2}{18\mu}}</math></center>
<br/>
<br/>
----
----
{{ACContribs
{{ACContribs
| authors=Martin Sommerfeld
| authors=Martin Sommerfeld
| organisation=Martin-Luther-Universitat Halle-Wittenberg
| organisation=Martin-Luther-Universität Halle-Wittenberg
}}
}}
{{ACHeader
{{ACHeader_ref
|area=3
|area=3
|number=12
|number=12

Latest revision as of 16:18, 11 February 2017

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References

Particle-laden swirling flow

Application Challenge AC3-12   © copyright ERCOFTAC 2013

Introduction

The special features of swirling flows are utilised in combustion systems in order to provide flame stabilisation and good mixing between fuel and oxidiser. This is achieved by the central recirculation bubble developing in front of the burner exit. Swirl burners are usually operated with liquid (spray) or pulverised fuels.

In order to obtain a better understanding of the particle behaviour in such a complex swirling flow, detailed experiments were conducted on particle-laden swirling flow emanating into a pipe expansion (Sommerfeld and Qiu 1991). The gas-particle mixture was injected centrally without swirl together with a co-flowing swirling annular gas jet yielding a swirl number of about 0.5. Downstream of the inlet simultaneous measurements of gas and particle velocities (all three components) were conducted by phase-Doppler anemometry, which also provided local particle size distributions and the stream-wise particle mass flux. Two cases with different injection flow rates, but roughly identical swirl number were considered. Both cases showed a closed central recirculation region. Inlet conditions are available from highly resolved profiles 3 mm downstream of the edge of the inflow tubes. Since the particle mass loading is rather small two-way coupling effects are of minor importance. Numerical computations performed with the finite-volume code FASTEST in connection with the k-ε turbulence model showed reasonable good agreement with the measurements (Sommerfeld and Qiu 1993). The particle phase was simulated by Lagrangian tracking also yielding a quite good agreement with measured velocity profiles, the particle mass flux and the number mean particle diameter.

Relevance to Industrial Sector

Particle- or droplet-laden swirling gas flows are found in numerous technical applications. In spray or coal fired combustion systems, swirling flows are used to establish very high mixing rates between fuel and swirling air stream and to ensure the required flame stability. This is achieved by the developing central recirculation region, where the hot reaction products are convected backward and mix with the fresh fuel and air.

In addition particle-laden swirling flows are found in numerous different types of particle separation devices, such as air cyclones. The considered basic flow configuration allows detailed validation of computations for particle-laden swirling flows, especially with respect to Reynolds-stress turbulence modelling or LES applications and particle dispersion in anisotropic turbulence.

Design or Assessment Parameters

The assessment parameters for this test case are the mean velocity profiles as well as those for the rms values along the test section for both phases. Additionally, profiles of the stream-wise particle mass flux could be estimated from the measurements revealing the centrifuging effect of a swirling flow. From the numerical calculations also the particle residence time as a function of particle size may be used to assess the performance of numerical calculations.

Flow Domain Geometry

The swirling flow was realized in a kind of pipe expansion flow (Figure 1).

Through the central inlet tube (diameter 32 mm) the gas-particle mixture was injected into the test section without swirl. The co- flowing swirling flow was produced by a vane-swirl generator located upstream the inlet. The annular inlet tube has an inner diameter of 38 mm and an outer diameter of 64 mm. The test section has a diameter of 194 mm and a length of 1,500 mm. The end of the test section is connected to a sufficiently wide stagnation chamber.


AC3-12 fig1.png
Figure 1: Swirl Flow test section made from Plexiglas including the main dimensions (length 1,500 mm).

Flow Physics and Fluid Dynamics Data

The considered swirling flow is highly turbulent, but may be considered as incompressible. The measurements were done under ambient conditions with a temperature of about 300 K yielding an air density of 1.18 kg/m3 and a dynamic viscosity of 18.4×10-6 kg/(m·s). The characteristic non- dimensional parameters are:


The flow Reynolds number, which is calculated with the total volume flow rate, the outer diameter of the annulus and the effective inlet cross- sectional area Ain:

The swirl number, which is the ratio of the axial flux of annular momentum to the axial flux of linear momentum obtained by integration across the primary and annular inlets:


Here U and W are the mean axial and tangential velocities and r is the radius. The values of the outer diameter of the inlet, D3, and the inner diameter of the test section D5 are given in Figure 1. The Reynolds numbers of the two cases considered are 52400 and 54500 and the swirl numbers are around 0.5.

As mentioned above, the particle mass loading was rather low so that the effect of the particles on the flow field may be neglected. The particles are spherical glass beads with a material density of 2,500 kg/m3 and a relative wide size distribution ranging between about 10 µm to 80 µm. The number mean diameter (mean diameter based on particle counts) is 45 µm yielding a mean Stokesian response time of about 15 ms.




Contributed by: Martin Sommerfeld — Martin-Luther-Universität Halle-Wittenberg

Front Page

Description

Test Data

CFD Simulations

Evaluation

Best Practice Advice

References


© copyright ERCOFTAC 2013