Upload
rajeev-kt
View
156
Download
2
Embed Size (px)
Citation preview
Non-dimensionalisation of the Navier-Stokes equations
Michal Kopera
Centre for Scientific Computing
24 January 2008
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Outline
Previously on Research Seminar ...
Navier-Stokes equations (vector and tensor notation)
Different forms of Navier-Stokes equations
Divergent
Dissipative
Skew-symmetric
Rotational
Non-dimensionalization
Dimensionless variables
Derivations of dimensionless equations
Choosing the reference values
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Previously on Research Seminar...
Continuity equation
∂ρ
∂t+∂(ρu)
∂x+∂(ρv)
∂y+∂(ρw)
∂z= 0
Assumptions
Infinitesimal control volume, but big enough to treat the fluid as acontinuum
ρ = const.
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Previously on Research Seminar...
Continuity equation
∂ρ
∂t+∂(ρu)
∂x+∂(ρv)
∂y+∂(ρw)
∂z= 0
Assumptions
Infinitesimal control volume, but big enough to treat the fluid as acontinuum
ρ = const.
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Previously on Research Seminar...
Continuity equation
∂ρ
∂t+∂(ρu)
∂x+∂(ρv)
∂y+∂(ρw)
∂z= 0
Assumptions
Infinitesimal control volume, but big enough to treat the fluid as acontinuum
ρ = const.
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Previously on Research Seminar...
Continuity equation for incompressible fluid
∂u
∂x+∂v
∂y+∂w
∂z= 0
∇~V = 0
∂ui
∂xi= 0
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Previously on Research Seminar...
Continuity equation for incompressible fluid
∂u
∂x+∂v
∂y+∂w
∂z= 0
∇~V = 0
∂ui
∂xi= 0
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Previously on Research Seminar...
Continuity equation for incompressible fluid
∂u
∂x+∂v
∂y+∂w
∂z= 0
∇~V = 0
∂ui
∂xi= 0
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Previously on Research Seminar...
Linear momentum equation
ρ∂~V
∂t+ ρ(~V · ∇)~V = ρ~g −∇p +∇τij
ρ∂ui
∂t+ ρuj
∂ui
∂xj= ρgi −
∂p
∂xi+∂τij∂xj
Assumptions
Newtonian fluid: τij = µ(∂ui∂xj
+∂uj
∂xi
)
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Previously on Research Seminar...
Linear momentum equation
ρ∂~V
∂t+ ρ(~V · ∇)~V = ρ~g −∇p +∇τij
ρ∂ui
∂t+ ρuj
∂ui
∂xj= ρgi −
∂p
∂xi+∂τij∂xj
Assumptions
Newtonian fluid: τij = µ(∂ui∂xj
+∂uj
∂xi
)
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Previously on Research Seminar...
Linear momentum equation
ρ∂~V
∂t+ ρ(~V · ∇)~V = ρ~g −∇p +∇τij
ρ∂ui
∂t+ ρuj
∂ui
∂xj= ρgi −
∂p
∂xi+∂τij∂xj
Assumptions
Newtonian fluid: τij = µ(∂ui∂xj
+∂uj
∂xi
)
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Previously on Research Seminar...
Linear momentum equation for Newtonian fluid
∂~V
∂t+ (~V · ∇)~V = ~g − 1
ρ∇p + ν4~V
∂ui
∂t+ uj
∂ui
∂xj= gi −
1
ρ
∂p
∂xi+ ν
∂2ui
∂xj∂xj
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Previously on Research Seminar...
Linear momentum equation for Newtonian fluid
∂~V
∂t+ (~V · ∇)~V = ~g − 1
ρ∇p + ν4~V
∂ui
∂t+ uj
∂ui
∂xj= gi −
1
ρ
∂p
∂xi+ ν
∂2ui
∂xj∂xj
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Previously on Research Seminar...
Energy equation
ρdu
dt+ p(∇ · ~V ) = ∇(k · ∇T ) + Φ
Assumptions
Fourier law: ~q = −k∇T
du ≈ cvdT ≈ cpdT
cv , cp, µ, k , ρ ≈ const.
Φ = 0
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Previously on Research Seminar...
Energy equation
ρdu
dt+ p(∇ · ~V ) = ∇(k · ∇T ) + Φ
Assumptions
Fourier law: ~q = −k∇T
du ≈ cvdT ≈ cpdT
cv , cp, µ, k , ρ ≈ const.
Φ = 0
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Previously on Research Seminar...
Energy equation
ρdu
dt+ p(∇ · ~V ) = ∇(k · ∇T ) + Φ
Assumptions
Fourier law: ~q = −k∇T
du ≈ cvdT ≈ cpdT
cv , cp, µ, k , ρ ≈ const.
Φ = 0
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Previously on Research Seminar...
Energy equation
ρdu
dt+ p(∇ · ~V ) = ∇(k · ∇T ) + Φ
Assumptions
Fourier law: ~q = −k∇T
du ≈ cvdT ≈ cpdT
cv , cp, µ, k , ρ ≈ const.
Φ = 0
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Previously on Research Seminar...
Energy equation for an incompressible flow without viscous dissipation
∂T
∂t+ (~V · ∇)T =
k
ρcp4T
∂T
∂t+ uj
∂T
∂xj=
k
ρcv
∂2T
∂xj∂xj
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Previously on Research Seminar...
Energy equation for an incompressible flow without viscous dissipation
∂T
∂t+ (~V · ∇)T =
k
ρcp4T
∂T
∂t+ uj
∂T
∂xj=
k
ρcv
∂2T
∂xj∂xj
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Different forms of the Navier-Stokes equation
convective form
∂ui
∂t+ uj
∂ui
∂xj= gi −
1
ρ
∂p
∂xi+ ν
∂2ui
∂xj∂xj
divergent form
∂ui
∂t+∂(uiuj)
∂xj= gi −
1
ρ
∂p
∂xi+ ν
∂2ui
∂xj∂xj
skew-symmetric form
∂ui
∂t+
1
2uj∂ui
∂xj+
1
2
∂(uiuj)
∂xj= gi −
1
ρ
∂p
∂xi+ ν
∂2ui
∂xj∂xj
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Different forms of the Navier-Stokes equation
convective form
∂ui
∂t+ uj
∂ui
∂xj= gi −
1
ρ
∂p
∂xi+ ν
∂2ui
∂xj∂xj
divergent form
∂ui
∂t+∂(uiuj)
∂xj= gi −
1
ρ
∂p
∂xi+ ν
∂2ui
∂xj∂xj
skew-symmetric form
∂ui
∂t+
1
2uj∂ui
∂xj+
1
2
∂(uiuj)
∂xj= gi −
1
ρ
∂p
∂xi+ ν
∂2ui
∂xj∂xj
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Different forms of the Navier-Stokes equation
convective form
∂ui
∂t+ uj
∂ui
∂xj= gi −
1
ρ
∂p
∂xi+ ν
∂2ui
∂xj∂xj
divergent form
∂ui
∂t+∂(uiuj)
∂xj= gi −
1
ρ
∂p
∂xi+ ν
∂2ui
∂xj∂xj
skew-symmetric form
∂ui
∂t+
1
2uj∂ui
∂xj+
1
2
∂(uiuj)
∂xj= gi −
1
ρ
∂p
∂xi+ ν
∂2ui
∂xj∂xj
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Different forms of the Navier-Stokes equation
rotational form
∂~V
∂t+ (∇× ~V )× ~V +∇
(1
2|~V |2
)= ~g − 1
ρ∇p + ν4~V
~ω = ∇× ~V
P = p +1
2ρ|~V |2
∂~V
∂t+ ~ω × ~V = ~g − 1
ρ∇P + ν4~V
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Different forms of the Navier-Stokes equation
rotational form
∂~V
∂t+ (∇× ~V )× ~V +∇
(1
2|~V |2
)= ~g − 1
ρ∇p + ν4~V
~ω = ∇× ~V
P = p +1
2ρ|~V |2
∂~V
∂t+ ~ω × ~V = ~g − 1
ρ∇P + ν4~V
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Different forms of the Navier-Stokes equation
rotational form
∂~V
∂t+ (∇× ~V )× ~V +∇
(1
2|~V |2
)= ~g − 1
ρ∇p + ν4~V
~ω = ∇× ~V
P = p +1
2ρ|~V |2
∂~V
∂t+ ~ω × ~V = ~g − 1
ρ∇P + ν4~V
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Different forms of the Navier-Stokes equation
convective term in tensor notation
(∇× ~V )× ~V +∇(
1
2|~V |2
)→ uj
(∂ui
∂xj−∂uj
∂xi
)+
∂
∂xi
(1
2ujuj
)rotational form in tensor notation
∂ui
∂t+ uj
(∂ui
∂xj−∂uj
∂xi
)= gi −
1
ρ
∂P
∂xi+ ν
∂2ui
∂xj∂xj
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Different forms of the Navier-Stokes equation
convective term in tensor notation
(∇× ~V )× ~V +∇(
1
2|~V |2
)→ uj
(∂ui
∂xj−∂uj
∂xi
)+
∂
∂xi
(1
2ujuj
)rotational form in tensor notation
∂ui
∂t+ uj
(∂ui
∂xj−∂uj
∂xi
)= gi −
1
ρ
∂P
∂xi+ ν
∂2ui
∂xj∂xj
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Different forms of the Navier-Stokes equation
Summary of the Navier-Stokes equation formulations
convective ∂ui∂t + uj
∂ui∂xj
= gi − 1ρ∂p∂xi
+ ν ∂2ui∂xj∂xj
divergent ∂ui∂t +
∂(uiuj )∂xj
= gi − 1ρ∂p∂xi
+ ν ∂2ui∂xj∂xj
skew-symmetric ∂ui∂t + 1
2uj∂ui∂xj
+ 12∂(uiuj )∂xj
= gi − 1ρ∂p∂xi
+ ν ∂2ui∂xj∂xj
rotational ∂ui∂t + uj
(∂ui∂xj− ∂uj
∂xi
)= gi − 1
ρ∂P∂xi
+ ν ∂2ui∂xj∂xj
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Non-dimensionalization - Dimensionless variables
Dimensionless variables
a - variable which has a dimension (unit) (length, velocity)
A - reference constant (eg. length of a football pitch, free streamvelocity)
a∗ = aA - dimensionless variable
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Non-dimensionalization - Dimensionless variables
Dimensionless variables
a - variable which has a dimension (unit) (length, velocity)
A - reference constant (eg. length of a football pitch, free streamvelocity)
a∗ = aA - dimensionless variable
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Non-dimensionalization - Dimensionless variables
Dimensionless variables
a - variable which has a dimension (unit) (length, velocity)
A - reference constant (eg. length of a football pitch, free streamvelocity)
a∗ = aA - dimensionless variable
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Non-dimensionalization - Continuity equation
Continuity equation
∂ui
∂xi= 0
Dimensionless variables
u∗i = uiU x∗i = xi
L
Non-dimensional continuity equation
∂u∗i∂x∗i
= 0
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Non-dimensionalization - Continuity equation
Continuity equation
∂ui
∂xi= 0
Dimensionless variables
u∗i = uiU x∗i = xi
L
Non-dimensional continuity equation
∂u∗i∂x∗i
= 0
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Non-dimensionalization - Continuity equation
Continuity equation
∂ui
∂xi= 0
Dimensionless variables
u∗i = uiU x∗i = xi
L
Non-dimensional continuity equation
∂u∗i∂x∗i
= 0
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Non-dimensionalization - Momentum equation
Linear momentum equation
∂ui
∂t+ uj
∂ui
∂xj= gi −
1
ρ
∂p
∂xi+ ν
∂2ui
∂xj∂xj
Dimensionless variables
u∗i = uiU x∗i = xi
L t∗ = t UL p∗ = p
ρU2
Non-dimensional momentum equation
∂u∗i∂t∗
+ u∗j∂u∗i∂x∗j
= giL
U2− ∂p∗
∂x∗i+
ν
UL
∂2u∗i∂x∗j ∂x∗j
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Non-dimensionalization - Momentum equation
Linear momentum equation
∂ui
∂t+ uj
∂ui
∂xj= gi −
1
ρ
∂p
∂xi+ ν
∂2ui
∂xj∂xj
Dimensionless variables
u∗i = uiU x∗i = xi
L t∗ = t UL p∗ = p
ρU2
Non-dimensional momentum equation
∂u∗i∂t∗
+ u∗j∂u∗i∂x∗j
= giL
U2− ∂p∗
∂x∗i+
ν
UL
∂2u∗i∂x∗j ∂x∗j
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Non-dimensionalization - Momentum equation
Linear momentum equation
∂ui
∂t+ uj
∂ui
∂xj= gi −
1
ρ
∂p
∂xi+ ν
∂2ui
∂xj∂xj
Dimensionless variables
u∗i = uiU x∗i = xi
L t∗ = t UL p∗ = p
ρU2
Non-dimensional momentum equation
∂u∗i∂t∗
+ u∗j∂u∗i∂x∗j
= giL
U2− ∂p∗
∂x∗i+
ν
UL
∂2u∗i∂x∗j ∂x∗j
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Non-dimensionalization - Momentum equation
∂u∗i∂t∗
+ u∗j∂u∗i∂x∗j
= giL
U2− ∂p∗
∂x∗i+
ν
UL
∂2u∗i∂x∗j ∂x∗j
Dimensionless parameters
Reynolds number: Re = ULν (always important)
Froude number: Fr = U2
gL (only if there is a free surface)
Non-dimensional momentum equation with dimensionless parameters
∂u∗i∂t∗
+ u∗j∂u∗i∂x∗j
=1
Fr− ∂p∗
∂x∗i+
1
Re
∂2u∗i∂x∗j ∂x∗j
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Non-dimensionalization - Energy equation
Energy equation
∂T
∂t+ uj
∂T
∂xj=
k
ρcp
∂2T
∂xj∂xj
Dimensionless variables
u∗i = uiU x∗i = xi
L t∗ = t · t0 T ∗ = T−T0T1−T0
Non-dimensional energy equation
T1 − T0
t0
∂T ∗
∂t∗+
U
L(T1 − T0)u∗j
∂T ∗
∂x∗j=
k
ρcp
T1 − T0
L2
∂T ∗
∂x∗j ∂x∗j
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Non-dimensionalization - Energy equation
Energy equation
∂T
∂t+ uj
∂T
∂xj=
k
ρcp
∂2T
∂xj∂xj
Dimensionless variables
u∗i = uiU x∗i = xi
L t∗ = t · t0 T ∗ = T−T0T1−T0
Non-dimensional energy equation
T1 − T0
t0
∂T ∗
∂t∗+
U
L(T1 − T0)u∗j
∂T ∗
∂x∗j=
k
ρcp
T1 − T0
L2
∂T ∗
∂x∗j ∂x∗j
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Non-dimensionalization - Energy equation
Energy equation
∂T
∂t+ uj
∂T
∂xj=
k
ρcp
∂2T
∂xj∂xj
Dimensionless variables
u∗i = uiU x∗i = xi
L t∗ = t · t0 T ∗ = T−T0T1−T0
Non-dimensional energy equation
T1 − T0
t0
∂T ∗
∂t∗+
U
L(T1 − T0)u∗j
∂T ∗
∂x∗j=
k
ρcp
T1 − T0
L2
∂T ∗
∂x∗j ∂x∗j
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Non-dimensionalization - Energy equation
T1 − T0
t0
∂T ∗
∂t∗+
U
L(T1 − T0)u∗j
∂T ∗
∂x∗j=
k
ρcp
T1 − T0
L2
∂T ∗
∂x∗j ∂x∗j
Dimensionless parameters
Reynolds number: Re = ULν
Prandtl number: Pr =µcp
k
Strouhal number: St = LUt0
Non-dimensional energy equation with dimensionless parameters
St∂T ∗
∂t∗+ u∗j
∂T ∗
∂x∗j=
1
RePr
∂T ∗
∂x∗j ∂x∗j
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Non-dimensionalization - Energy equation
T1 − T0
t0
∂T ∗
∂t∗+
U
L(T1 − T0)u∗j
∂T ∗
∂x∗j=
k
ρcp
T1 − T0
L2
∂T ∗
∂x∗j ∂x∗j
Dimensionless parameters
Reynolds number: Re = ULν
Prandtl number: Pr =µcp
k
Strouhal number: St = LUt0
Non-dimensional energy equation with dimensionless parameters
St∂T ∗
∂t∗+ u∗j
∂T ∗
∂x∗j=
1
RePr
∂T ∗
∂x∗j ∂x∗j
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Non-dimensionalization - Summary
Summary of dimensionless Navier-Stokes equations
continuity∂u∗i∂x∗i
= 0
momentum∂u∗i∂t∗ + u∗j
∂u∗i∂x∗j
= 1Fr −
∂p∗
∂x∗i+ 1
Re∂2u∗i∂x∗j ∂x∗j
energy St ∂T∗
∂t∗ + u∗j∂T∗
∂x∗j= 1
RePr∂T∗
∂x∗j ∂x∗j
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations
Non-dimensionalization - choosing the parameters
Now how to choose the U, L etc. ?
Michal Kopera Non-dimensionalisation of the Navier-Stokes equations