Abstract
In this contribution a particular plane steady-state channel flow including evaporation effects is investigated from analytical point of view. The channel is assumed to be horizontal. The motion of two heavy viscous immiscible fluids is governed by a free boundary value problem for a coupled system of Navier-Stokes and Stephan equations. The flow domain is unbounded in two directions and the free interface separating partially both liquids is semi-infinite, i.e. infinite in one direction. The free interface begins in some point Q where the half-line Σ1 separating the two parts of the channel in front of Q ends. Existence and uniqueness of a suitable solution in weighted HÖLDER spaces can be proved for small data (i.e. small fluxes) of the problem.
1 Introduction
In this paper we are concerned with the investigation of a particular free boundary value problem (= BVP) for a two-fluid non-isothermal channel flow. The infinite channel is assumed to be horizontal and it contains a partial inner wall (cf. the thin red line Σ1 in Figure 1) which is semi-infinite. The flow problem is assumed to be stationary and 2D. In Figure 1 the blue line denotes the lower channel wall which moves with constant speed R in x1-direction. The red line Σ2 denotes the upper channel wall that is at rest. Finally, by the cyan curve Γ we understand the a priori unknown free interface between the two fluid layers. It has the representation x2 = φ(x1) where the function φ has to be found as well as the flow fields for velocity v(x), for the pressure p(x) and for the temperature θ(x).

Flow domain of a two-fluid channel flow
Models of the described kind are quite important in many technological and scientific applications. Corresponding examples may be found in the field of materials science, particularly in coating and solidification processes with evaporation or in crystal-growth processes (cf. [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]). The investigations of such problems are performed from technical point of view as well as from analytical and/or numerical point of view. It was our main objective to obtain statements about the existence and/or uniqueness of free BVP for evaporation problems.
The flow describes a coupled heat-and mass transfer (Stephan equations). The (positive) fluxes Fm are prescribed in each fluid layer Ωm (m = 1,2) (cf. Fig. 1). The lower liquid layer is characterized by red color whereas the upper one is marked by green color. Both liquids are heavy, viscous, heat-conducting, incompressible and immiscible. Therefore, the mathematical model can incorporate evaporation effects. The surface tension σ(θ) is temperature-depending in a known manner.
By νm, ηm and λm (m = 1,2) we understand the domain-wise (i.e. regional) constant values of the kinematic viscosity, of the density and of the thermal conductivity, respectively, of the m-th fluid. By h∞ we denote the (asymptotic) position of the free interface Γ when x1 goes to +∞. By {n, τ, respectively, the unit normal and the unit tangential vectors with respect to Γ are denoted. Their orientation (direction) is the same as for x1, x2. By g and eg we understand the acceleration and the direction of gravity, respectively. Concerning the interface tension σ we suppose the following linear function of temperature θ
which is frequently used in the literature. This leads to an effect which is called Benard-Marangoni-effect or thermo-capillary convection. Finally, the following symbols and abbreviations have been used throughout this paper: δj(t) : = {x1 = t} ∩ Ωj, j = 1,2} is some cross section of Ωj. The frictional stress tensor has the subsequent elements: Sjk = ν η(∂kvj + ∂jvk) (j,k = 1,2). The symbol [w(x0)]|Γ represents the jump of the field w crossing the interface Γ from below to above:
2 Mathematical model
The governing equations (Navier - Stokes & Stephan) of the problem which yield in Ω : = Ω1 ∪ Ω2 read as follows
They are supplied by the boundary conditions at the lower moving wall Σ0:
Let us emphasize that the value 0 in Eq. (2) does not represent the absolute temperature but some dimensionless value which is in fact the difference to some reference temperature related to a characteristic temperature difference.
The boundary conditions at the walls at rest Σk (k = 1,2) look like:
Let us explain that the boundary conditions (3) for k = 1 mean both sides
As a consequence one gets the relation: limx1 → +∞φ (x1) = const. = h∞.
In order to prove the unique solvability of the BVP in appropriate functional spaces the following two-cycle iteration scheme was applied.
This scheme was introduced by V.V. Pukhnachev and V.A. Solonnikov about 45 years ago (cf. e.g. [13, 14] or [15]). The two-cycle iteration scheme was also applied in the papers [14, 15] and by the author in [9, 16]. In the references [11, 17, 18] other methods are used to handle different free BVP.
The scheme (5) is very senseful in cases where the free boundary is semi-infinite. In a first cycle the three flow fields v, p, θ are computed in a flow domain with fixed boundaries neglecting one of the boundary conditions - mostly the normal stress condition (4)5, i.e. the 5th equation in (4). This first cycle is then divided into several steps: The linear problem with fixed boundary containing the corresponding estimates for the solution, a model problem at the separation point Q for the determination of the weight functions, the regularity of the solutions at infinity and then the nonlinear problem with fixed boundary.
In a second stage the neglected boundary condition is used in order to compute a new shape of the free boundary (and simultaneously a new shape of the entire flow domain). This equation is usually
where K(x1) denotes the curvature of Γ in x1 and it is equal to the left-hand side of Eq. (4)5. In both cycles a related linear problem is solved and the continuous dependence of the solutions on the boundary data is also proved. Then BANACH‘s fixed point argument related to some contraction operator 𝔅 shows the remaining parts for small data.
3 Function spaces
First of all we define some weighted HÖLDER spaces. Let B be an arbitrary domain in ℝ2 and N ⊂ B a manifold of dimension n < 2. Define further ϱN(x) : = dist (x,N). By β = (β1,β2) we understand a multiindex, and ⌊ r ⌋ is the integer part of r. Then by Cr(B) (r > 0, non-integer) we mean the well-known HÖLDER space with a finite norm
Let us remark that the weight functions in (6) represent some kind of power functions with respect to the distance from the singularity points. For (r > s > 0; r,s non-integer) we get the space
The spaces
Furthermore,
Also,
By
Finally, the weighted HÖLDER spaces containing the generalized solutions, are
They are essentially used throughout this paper and their norms are given by
The weight functions here in formula (8) are exponential functions and they decay at the infinities. As above, we obtain for our double channel
At the end, for functions of one real variable we deal with the space
4 On the Basic Flow for Large x1
In this section we are interested in getting an approriate starting (or initial) solution for the iteration scheme (5). For this purpose, and under the assumptions
we calculate for given values F1, F2, R, θ0 = 0, θ1, θ2 and associated rheological parameters the flow fields and values v(x), p(x), θ (x), p0, h∞, θ∞. The value θ∞ which has not been defined before describes the (asymptotic) value of the temperature θ at the free interface when x1 goes to +∞. Let us emphasize that the assumptions guarantee solution fields that are uniform and unidirectional (not depending on main-stream direction x1).
Under the assumptions (9) the governing Eqs. (1) take the subsequent reduced form:
where the second equation replaces the continuity Eq. (1)2 Now it is possible to divide the original problem into three independent problems for the flow fields. Let us start with the problem for velocities v:
For the pressure p one obtains the following equations
Finally, the problem for temperature θ reads
In Eqs. (10), (11), (12) the superscripts (k), (k = 1, 2) or (+) denote the corresponding fluid layer and the subregion x1 ⩾ 1. The solutions of these three (independent) problems are of NUSSELT type (cf. also [19]) and allow the representation
The coefficients in (13) are given by
Note, that the values h∞ and p0 are already known for these expressions (see Eq. (16) below). That is why it follows θ∞ = (λ2θ2h∞)/[λ1 (1−h∞) + λ2h∞] and for the complete temperature and pressure fields one obtains
Since the associated linear problem is completely decomposed, we got the same polynomial equation for the determination of the value h∞ as in the former paper [17].
In [17] the subsequent two lemmas were proved.
Lemma 4.1
If F1F2 > 0, then Eq. (16)has at least one root h∞within the open interval ]0, 1[.
Lemma 4.2
If F1F2 ⩾ 0, then Eq. (16)has at most three different roots h∞ ∈]0, 1[.
Note that in the subregion
In
It is well-known that the pressure p can be determined only up to an additive constant in channel flows (cf. k1, k2 in formulae (17), (18)).
5 The free interface equation
Eq. (16) coincides with equation (A.13) from [17] for horizontal channels. Recall that the final thickness h∞ is a function of F1, F2, R and of the rheological parameters of the fluids. It can have up to three different values in the open interval ]0, 1[ for the same parameter set (cf. [17]). Furthermore, by φ(+) (x1) we denote the infinitely differentiable solution of the following free BVP.
which can be obtained from the 5-th condition (4)5 of (4) by setting v = 0, p = const., θ = 0 as the initial solution for F1 = F2 = R = θ0 = θ2 = 0. Let ξ = ξ(x1) be a smooth cut-off function vanishing for |x1| ⩽ 1 and being equal to 1 for |x1| ⩾ 2. Finally, assume that η1 > η2 is satisfied. This makes physically sense.
Now, the difference function ω (x1) := (φ (x1) − φ(+) (x1)) is equivalent to
The remaining part of the proof of the main theorem is a slightly modified repetition of the proof of Theorem 8.1 in [20]. First of all, one has to study the dependence of the solution to the nonlinear auxiliary problem with fixed boundary on small variations of the boundary. After getting the corresponding estimates one applies BANACH’s fixed point principle to the subsequent operator equation. Instead of the operator Eq. (8.10) from [20] we have to study the following one:
with 𝔗(3) given in (20) and the other parts taken from [20]. Since 𝔗(3) is a contraction operator for small θ, we can conclude as in [20] that 𝔅 is a contraction operator in the ball
6 Results
Let us formulate the main result of this contribution. A sketch of the proof has been given before. A very detailed application of this method can be found in the thesis [16] as well as in the article [20].
Theorem 6.1
There exist positive real numbers
the complete mathematical model has a unique solution {v, p, θ, φ} which can be represented in the form
where ξ is the cut-off function described above, (v(−), p(−), θ(−)) is the basic exact solution given by(17), (18)in both channels on left-hand side. The function φ(+)is the solution to the free BVP (19). Moreover, ϑ0, w ∈
Remark 6.2
If Eq. (16)has more than one real root h∞between 0 and 1 then the statements of Theorem 6.1 remain true in the neighbourhood of each value.
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© 2018 Socolowsky, published by De Gruyter
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- On a viscous two-fluid channel flow including evaporation
- Generation of pseudo-random numbers with the use of inverse chaotic transformation
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- Monotone subsequence via ultrapower
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- On the security of the Courtois-Finiasz-Sendrier signature
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- Rank relations between a {0, 1}-matrix and its complement
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- Time parallelization scheme with an adaptive time step size for solving stiff initial value problems
- Stability problems and numerical integration on the Lie group SO(3) × R3 × R3
- On some fixed point results for (s, p, α)-contractive mappings in b-metric-like spaces and applications to integral equations
- On algebraic characterization of SSC of the Jahangir’s graph 𝓙n,m
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- On nonlinear evolution equation of second order in Banach spaces
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- On new strong versions of Browder type theorems
- A Geršgorin-type eigenvalue localization set with n parameters for stochastic matrices
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- Singular integrals with variable kernel and fractional differentiation in homogeneous Morrey-Herz-type Hardy spaces with variable exponents
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- Restricted triangulation on circulant graphs
- Boundedness control sets for linear systems on Lie groups
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- Generalizations of Steffensen’s inequality via the extension of Montgomery identity
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- On Banach and Kuratowski Theorem, K-Lusin sets and strong sequences
- On the boundedness of square function generated by the Bessel differential operator in weighted Lebesque Lp,α spaces
- On the different kinds of separability of the space of Borel functions
- Curves in the Lorentz-Minkowski plane: elasticae, catenaries and grim-reapers
- Functional analysis method for the M/G/1 queueing model with single working vacation
- Existence of asymptotically periodic solutions for semilinear evolution equations with nonlocal initial conditions
- The existence of solutions to certain type of nonlinear difference-differential equations
- Domination in 4-regular Knödel graphs
- Stepanov-like pseudo almost periodic functions on time scales and applications to dynamic equations with delay
- Algebras of right ample semigroups
- Random attractors for stochastic retarded reaction-diffusion equations with multiplicative white noise on unbounded domains
- Nontrivial periodic solutions to delay difference equations via Morse theory
- A note on the three-way generalization of the Jordan canonical form
- On some varieties of ai-semirings satisfying xp+1 ≈ x
- Abstract-valued Orlicz spaces of range-varying type
- On the recursive properties of one kind hybrid power mean involving two-term exponential sums and Gauss sums
- Arithmetic of generalized Dedekind sums and their modularity
- Multipreconditioned GMRES for simulating stochastic automata networks
- Regularization and error estimates for an inverse heat problem under the conformable derivative
- Transitivity of the εm-relation on (m-idempotent) hyperrings
- Learning Bayesian networks based on bi-velocity discrete particle swarm optimization with mutation operator
- Simultaneous prediction in the generalized linear model
- Two asymptotic expansions for gamma function developed by Windschitl’s formula
- State maps on semihoops
- 𝓜𝓝-convergence and lim-inf𝓜-convergence in partially ordered sets
- Stability and convergence of a local discontinuous Galerkin finite element method for the general Lax equation
- New topology in residuated lattices
- Optimality and duality in set-valued optimization utilizing limit sets
- An improved Schwarz Lemma at the boundary
- Initial layer problem of the Boussinesq system for Rayleigh-Bénard convection with infinite Prandtl number limit
- Toeplitz matrices whose elements are coefficients of Bazilevič functions
- Epi-mild normality
- Nonlinear elastic beam problems with the parameter near resonance
- Orlicz difference bodies
- The Picard group of Brauer-Severi varieties
- Galoisian and qualitative approaches to linear Polyanin-Zaitsev vector fields
- Weak group inverse
- Infinite growth of solutions of second order complex differential equation
- Semi-Hurewicz-Type properties in ditopological texture spaces
- Chaos and bifurcation in the controlled chaotic system
- Translatability and translatable semigroups
- Sharp bounds for partition dimension of generalized Möbius ladders
- Uniqueness theorems for L-functions in the extended Selberg class
- An effective algorithm for globally solving quadratic programs using parametric linearization technique
- Bounds of Strong EMT Strength for certain Subdivision of Star and Bistar
- On categorical aspects of S -quantales
- On the algebraicity of coefficients of half-integral weight mock modular forms
- Dunkl analogue of Szász-mirakjan operators of blending type
- Majorization, “useful” Csiszár divergence and “useful” Zipf-Mandelbrot law
- Global stability of a distributed delayed viral model with general incidence rate
- Analyzing a generalized pest-natural enemy model with nonlinear impulsive control
- Boundary value problems of a discrete generalized beam equation via variational methods
- Common fixed point theorem of six self-mappings in Menger spaces using (CLRST) property
- Periodic and subharmonic solutions for a 2nth-order p-Laplacian difference equation containing both advances and retardations
- Spectrum of free-form Sudoku graphs
- Regularity of fuzzy convergence spaces
- The well-posedness of solution to a compressible non-Newtonian fluid with self-gravitational potential
- On further refinements for Young inequalities
- Pretty good state transfer on 1-sum of star graphs
- On a conjecture about generalized Q-recurrence
- Univariate approximating schemes and their non-tensor product generalization
- Multi-term fractional differential equations with nonlocal boundary conditions
- Homoclinic and heteroclinic solutions to a hepatitis C evolution model
- Regularity of one-sided multilinear fractional maximal functions
- Galois connections between sets of paths and closure operators in simple graphs
- KGSA: A Gravitational Search Algorithm for Multimodal Optimization based on K-Means Niching Technique and a Novel Elitism Strategy
- θ-type Calderón-Zygmund Operators and Commutators in Variable Exponents Herz space
- An integral that counts the zeros of a function
- On rough sets induced by fuzzy relations approach in semigroups
- Computational uncertainty quantification for random non-autonomous second order linear differential equations via adapted gPC: a comparative case study with random Fröbenius method and Monte Carlo simulation
- The fourth order strongly noncanonical operators
- Topical Issue on Cyber-security Mathematics
- Review of Cryptographic Schemes applied to Remote Electronic Voting systems: remaining challenges and the upcoming post-quantum paradigm
- Linearity in decimation-based generators: an improved cryptanalysis on the shrinking generator
- On dynamic network security: A random decentering algorithm on graphs