Global Existence and Large Time Behavior for the 2-D Compressible Navier-Stokes Equations without Heat Conductivity
Abstract
In this paper, we consider an initial value problem for the 2-D compressible Navier-Stokes equations without heat conductivity. We prove the global existence of a strong solution when the initial perturbation is small in H2 and its L1 norm is bounded. Moreover, we derive some decay estimate for such a solution.
1. Introduction
As one of the most important systems in fluid dynamics, there are lots of results on the well-posedness, blow-up phenomenon, large time or asymptotic behavior, and optimal decay rates of solutions based on different assumptions in different cases and function spaces. Among them, for the case with a positive coefficient of heat conduction k > 0, Kazhikhov and Shelukhin studied the global existence in one dimension [1, 2]. The global existence of multidimensional case was established in [3–6]; more results on global existence for different kinds of solutions can be found in [3–10]. For the study of the large time behavior, asymptotic behavior, and optimal decay rates of solutions, one can refer to [4, 11–15]. The references [15–17] and [10, 18] restricted the systems under the case of k = 0 and k > 0, respectively. Danchin [8, 9] proved the existence and uniqueness of strong solutions to the compressible Navier-Stokes equations in hybrid Besov spaces, and Tan and Wang [6] studied the global existence of strong small solutions in Hl, l ≥ 4. For the case of k = 0, Tan and Wang [5] proved the global solvability in three-dimensional space for the less regular solutions to the compressible Navier-Stokes equations in the H2-framework; however, they needed to assume that the L1-norm of the initial perturbation is bounded which is important in the proof of global existence. Later, ref. [3] removed this assumption by using some techniques with regard to the homogeneous Besov space and the hybrid Besov space.
Compared to the Cauchy problem, the equilibrium state of pressure increases with time. Xin et al. [16, 17, 19] investigated the blow-up phenomenon of the compressible Navier-Stokes equations in inhomogeneous Sobolev space; they proved that the smooth or strong solutions will blow up in any positive time if the initial data have an isolated mass group, no matter how small they are. On the other hand, we would like to introduce some research on the Serrin-type regularity (blow-up) criteria for the incompressible Navier-Stokes system. These criteria are obtained from [20, 21]; later, many authors successfully extended these blow-up criteria to the compressible flow (for example, [22–29] and references therein).
where p∞ > 0 and s∞ are the given constants. For the global existence and the decay estimate in the case of two dimensions, we have the following theorem.
Theorem 1. Let p∞ > 0, s∞ be two constants. There exists a small constant ε0 such that if , and are bounded, then there exists a unique global solution of the initial value problems (4) and (5) satisfying
Remark 2.
- (1)
The Lq decay estimates of (7) for 2 ≤ q ≤ 4 are optimal which coincide with the Lq decay of the heat equation and are much slower than the decay rate in ℝ3. In [3, 5], they obtain that which ensures that is bounded. But in ℝ2, we only have and therefore, is unbounded. This is the main difficulty about the proof of existence in ℝ2 (see Section 3 below)
- (2)
Due to k = 0, we cannot gain any diffusion of and the L∞ decay estimate of (7) is slower than the decay of the heat equation
1.1. Notation
In this paper, we use Lp, Hm to denote the Lp and Sobolev spaces on ℝ2 with norms and , respectively. We use C to denote the constants depending only on physical coefficients and C0 to be constants depending additionally on the initial data.
This paper is organized as follows: In Section 2, we reformulate problems (4) and (5), introduce two main propositions, and illustrate that we only need to prove Proposition 4. The rest of the paper is devoted to proving Proposition 4. The proof of the energy estimate part is in Section 3, and the decay rate part is in Section 4.
2. Reformulated System
Taking a standard contraction mapping argument, we have the following propositions for the local existence (see [30]).
Proposition 3 (see [3].)Suppose that the initial data satisfy (p0, v0, s0) ∈ H2(ℝ2) and . Then, there exists a positive constant T0 depending on such that Cauchy problem (9) has a unique solution (p, v, s) ∈ X(0, T0) satisfying
This, together with the proposition below, is sufficient to derive Theorem 1; the proof is based on the standard continuity argument.
Proposition 4. Let (p0, v0, s0) ∈ H2(ℝ2) and (p0, v0) ∈ L1(ℝ2); for any T > 0, there exists ε > 0 such that the solution (p, v, s) of the initial value problem (9) in [0, T] satisfies
The rest of paper is used to prove Proposition 4.
3. Energy Estimate
For later use, we introduce some useful analytic results.
Lemma 5. Let f ∈ H2(ℝ2); then, we have the following Sobolev inequalities:
Lemma 6 (lower-order energy estimate for (p, v)). Under the assumption of Proposition 4, there exists a δ1 > 0 arbitrarily small and independent of ε, such that
Proof. Multiplying (2.1)1, (2.1)2 by p, v, respectively, integrating them over ℝ2 and then adding them together, we obtain
〈p, f〉 and 〈v, g〉 can be estimated as follows. For the first term, Lemma 5 together with (14) and the Hölder inequality implies
For the second term,
Similar to the proof of (24), by Lemma 5, (14), the Hölder inequality, and the fact that
Therefore,
Hence, combining (23), (24), and (28) yields
Next, we shall estimate . Multiplying (2.1)2 by ∇p and integrating them over ℝ2, we get
Finally, multiplying (32) by δ1 that is small but fixed and adding it to (29), we can derive (22). This completes the proof of the lemma.
Next, we turn to estimate the higher-order energy for (p, v).
Lemma 7 (higher-order energy estimate for (p, v)). Under the assumption of Lemma 6, there is a small enough but fixed δ2 > 0, which is independent of ε, such that
Proof. Applying ∇ to (2.1)1, (2.1)2 and multiplying by ∇p, ∇v, respectively, integrating them over ℝ2 and using the same calculation technique as before, we get
Next, applying ∇2 to (2.1)1, (2.1)2 and multiplying by ∇2p, ∇2v, respectively, we can deduce
Thus,
Now applying ∇ to (2.1)2 and multiplying by ∇2p, we have
Similar to the estimate of , we transform the formula 〈−∇vt, ∇2p〉 as below:
Multiplying (42) by δ2 that is small but fixed, and combining it with (34) and (39), we finally obtain (33). This completes the proof of the lemma.
The lemma below gives the energy estimate for the entropy s.
Lemma 8. For 0 ≤ t ≤ T, it holds that
Proof. For each multi-index α with 0 ≤ |α| ≤ 2, we apply to (2.1)3, multiply it by , integrate it on ℝ2, and then sum them up to deduce
For W1, one has
where, for each α with 0 ≤ |α| ≤ 2, one can infer that
and for each α, β with 0 ≤ |β| ≤ |α| − 1, 1 ≤ |α| ≤ 2, and β ≤ α, it holds that
Therefore, we have
Now, we turn to estimate W2; using (14), we obtain
Now, we are in the position to prove the energy estimate in Proposition 4.
when ε is small enough. In other words, (15) is valid.
4. Decay Rates
In this section, we prove the decay rates in Proposition 4.
Proof of (17)–(20). Letting
Next, by adding to both sides of the above inequality, we deduce that for some constant α > 0,
To deal with , we rewrite the solution of system (9) as
where H(t) = (p(t), v(t)) and is a matrix-valued differential operator given by
and the solution semigroup has the following property (see [31, 32]).
Lemma 9. Let k > 0 be an integer; then, ∀t ≥ 0,
Then, gathering (63) and (65), one has
where and the nonlinear source can be estimated as follows:
for any 4 < q ≤ ∞, 0 ≤ t ≤ T. Therefore, the optimal decay rates (17)–(19) have been proven.
Therefore, (20) is finally proven.
5. Conclusion
The motivation of this paper is to refine the previous works of [3, 5]. As mentioned above, to prove the global existence of the compressible Navier-Stokes equations, ref. [3] needs to use some complicated techniques based on the notions of the homogeneous Besov space and the hybrid Besov space to remove a condition in [5]. However, in this paper, we use a much simpler method to achieve this, to complete a prior estimate on entropy which is important to prove the global existence of the compressible Navier-Stokes equations by some simple analysis.
The results are in the H2-framework; it is possible to consider similar problems in functional space with lower regularity.
Disclosure
The manuscript has been submitted as a preprint according to the following link: “https://www.authorea.com/users/488979/articles/572918-global-existence-and-decay-estimate-for-the-2-d-compressible-navier-stokes-equations-without-heat-conductivity.”
Conflicts of Interest
The authors declare that they have no conflicts of interest.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (no. 11901117).
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Data Availability
All data generated or analysed during this study are included in this published article.