fO^Cf\'T^-n2^ ^^» . dtt- tot i-k-ADON NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS TECHNICAL MEMORANDUM No. 1229 HEAT TRANSMISSION IN THE BOUNDARY LAYER By L. E, Kalikhman Translation of "Gazodinamicheckaya Teoriya Teploperedachi" Prikladnaya Matematika i Mekhanika, Tom X, 1946 Washington ADrill9i#^''^^^^'^°^^^°^'^^ Aprii -^y^yQcuMENTS DEPARTMENT 120 MARSTON SCIENCE UBRARY P.O. BOX 117011 GAINESVILLE, FL 32611-7011 USA ^3^ "^^0 >tP J75? NATIONAL ADVTSOEY COMMITTEE FOE AERONAUTICS TECHNICAL MEMORANDUM No. 1229 EEAT TRANSMISSION IN TKE BOUNDAEY LATER* By L. E. Kallldiman Up to the present time for the heat transfer along a curved wall in a gas flow only such prohlema have been solved for which the heat trans- fer between the wall and the incompressible fluid was considered with physical constants that were independent of the temperature (the hydro- dynamic theory of heat transfer). On this assumption, valid for gases only, for the case of small Madi numbers (the ratio of the velocity of the gas to that of sound) and small temperatiire drops between the flow and the wall, the velocity field does not depend on the temperature field. In 19^1 A. A. Dorodnitsyn (reference l) solved the problem on the effect of the compressibility of the gas on the boundary layer in the absence of heat transfer. In this case the relation between the tempera- ture field and the velocity field is given by the conditions of the problem (constancy of the total energy). In the present paper which deals with the heat transfer between the gas and the wall for large temperatiire drops and large velocities use is made of the above-mentioned method of Dorodnitsyn of the introduction of a new independent variable, with this difference, however, that the relation between the temperature field (that is, density) and the velocity field in the general case considered is not assumed given but is deter- mined from the solution of the problem. The effect of the compressibility arising from the heat transfer is thus taken into account (at the same time as the effect of the compressibility at the large velocities). A method is given for determining the coefficients of heat transfer and the friction coefficients required in many technical problems for a curved wall in a gas flow at large Mach nimbers and temperature drops. The method proposed is applicable both for Prandtl number P = 1 and for P ^ 1. "Gazodinamlcheckaya Teoriya Teploperedachi . " Prikladnaya Matematika i Mekhanika, Tom X, 19^6, pp. h^^^-k^k. NACA TM No. 1229 I. FUNDAMENTAL REIATIONS FOE THE lAMIKAE AND TURBULENT BOUNDAE?Y LAYER IN A GAS IN THE PRESENCE OF HEAT TRANSFER 1. Statement of the Problem We consider the flow over an arbitrary contour of the type of a wing profile in a steady two-dimensional gas flow (fig. l). For supersonic velocities we take into account the existence of an oblique density discontinuity (compression shock) starting at the sharp leading edge or a curvilinear head wave occurring ahead of the profile. For subsonic velocities we assume there are no shock waves (value of the Mach number of the approaching flow is less than the critical). We denote by u, v the components of the velocity along the axes X, J, where x is the distance along the arc of the profile from the leading edge, y is the distance along the normal, T ia the absolute temperature, p the pressure, p the density, \i the coefficient of viscosity, X the coefficient of heat transfer, e the coefficient of turbulence exchange, X^ the coefficient of turbulent heat conductivity, Cp the specific heat, and J the mechanical equivalent of heat. T = T + 2JCp is the stagnation temperature a = Kp is the velocity of sound is the adiabatic coefficient P - ^ is the Prandtl number. The remaining notation is explained in the text. The values of the magnitudes in the undisturbed flow are denoted by the subscript CO, the values of the magnitudes at the wall by the subscript w. The problem consists in the solution of the system of equations (reference 2) NACA TM No. 1229 (|i + e) ^ ^ ^ (pu) + ^ (pv) = (1.1) (1.2) (■ + V B ^ [,. O (S-) 57 ^1) (1.3) S7 = (i.i^) p = pRT, ^l = CT^ (1.5) where E is the gas constant, and C and n are constants. In the solution of the Bystam equations (l.l) to (1.5) we start out from, considerations on the dynamic and thermal houndary layer of a finite (hut variable) thickness. The flow outside the dynamic houndary layer approaches the ideal (nonviscous) flow, nonvortical in front of the shock wave and, in general, vortical behind the wave. Equation (l.^) shows that the pressure is transmitted across the boundary layer without change, that is, the pressure Po(2:) and the velocity on the boundary of the layer U(x) may be considered as given functions of x. The flow outside the thermal boundary layer we assume to occur without heat transfer, that is, outside the thermal layer and on its boundeory the total energy Iq 1b constant: JCpT + u^ U. JCpToo + = JCpTo (1.6) From this it follows that the stagnation temperature thermal boundary layer has a constant value i. outside the T* = _2. Jc, (1.7) Thus the flow outside the thermal boundary layer for small velocities is assumsd nearly Isothermal while for large subsonic velocities isentropic. NACA TM No. 1229 For supersonic velocities the entropy is constant" up to the shock wave while after the wave the entropy is constant alon^ each flow line of the external flow atout the profile but variable from one flow line to the nex±. The boundary conditions of the problem are: u = V = 0, T* = T^ f or y = (1.8) where T^ = T^(x) is a given function. In the absence of external heat transfer (across the wall) we have instead of the second condition of equation (1.8) the condition I j = 0. Further \Sy /y=:0 u = U(x) for y = 6^(x) 7' T* = T, 00 for y = Ay.(x) (1.9) where 5„ and A^. are the values of y referring, respectively, to the boundary of the dynamic and the boundary of the thermal layer. 2. Fundamental Expressions for the Temperatures For P = 1 equation (l.3) gives the "trivial integral" T* = Constant. Taking into account the second condition of equation (l.9)j we obtain T = Too(l-u2) 4 = -^\ (2.1) The temperature of the wall is equal to the temperature of the adiabatic stagnation: \ = Too = '^"f + 1^^ - 1)^^] P^o = ^) (2.2) The integral (2.1 ) corresponding to the case of the absence of external and internal heat transfer in the boundary layer, ( — ) = for P = 1, \Vy=0 was obtained on the basis of the solution of A. A. Dorodnltsyn (reference l), NACA TM No. 1229 ! For P = 1, U = Constant, emd T^ = Constant, equation (l.3) Is likewise integrated independent of tlie solution of the remaining eq^uations of the system and gives the so— called Stodola— Crocco integral T = au + b Imposing the "boundary conditions we ottain T = T, 00 l--^-(T,-l) (l-»)] {\ = l From equation (2.3) we also obtain w ^00/ (2.3) (2.U) u U (t = T - T^, to = Tqo - Tv) (2.5) The integral (2.J+) correspondB to the case -where there is similarity of the Telocity field with the field of the stagnation temperature drop (equation (2.5)) and was used in the solution of the problem of the flow about a flat plate (reference 3)« In any more general case U ^ Constant for (-lo ^ ° or T^^ / Constant or P ^ 1 the integral of (1.3) Is not known in advance. The existence of the trivial integral is not, however, the required condition for the solution of the problem and this fact is fundamental for what follows. Let the function T*(x, y) or u(x, y) be integrals of the system (l.l) to (1.5) satisfied by the boundary conditions (equations (I.8) and (1.9) )• The temperature at an arbitrary point can then be represented in the form ^00 Joo for '■00 -u2 (2.6) 1 - u^ + (T^ - 1) 1 NACA TM No. 1229 As Is easily seen, the integrals (2.l) and (2.U) are particular cases of - t* the second form of the relation (2.6) for T = 1 and — - = ^, ■to respectively. This relation permits expressing together with the temperature also the density and viscosity as a function of the velocity and stagnation temperature drop. 3. Expressions for the Pressure, Density, and Viscosity The pressure p at any point within the boundary layer is determined by the equation of Bernoulli P = Po = Po2(i-u2r r = 7= (3.1) where Pq is the pressure on the boundary of the layer (thermal or dynamic depending on which of them is thicker), Pqq is the pressure on adiabatically reducing the velocity to zero in the tube of flow passing through the shock wave. The density p at an arbitrary point within the boundary layer is determined by the equation of state (first equation of (1.5 )), equations (2.6) and (3.l) K P = Po2 li ;i-^ 77 pr^ (1 - ^^)'" (3.2) l-u2 + (T^-l)J^l-^^ where p^ is the density on adiabatic reduction of the velocity to zero. The viscosity p. is determined by the equation H = Hoo 1 - u^ + (Tw - 1)(1 ^) (n;^0.75) (3.3) where Hqq corresponds to the temperature Tqq, that Is, is obtained on the adiabatic reduction of the velocity ^o zero. NACA TM No. 1229 For any point ahead of the shock we have P = PoiCl - U2) K. K-1 J. P = P, 01 (i - ^y-"- (3.U) vhere Pq-, and Pq-, are, respectively, the pressure and density on adiahatlcally reducing the velocity to zero up to the intersection of the streamline with the shock. As a sc ale of the velocities it is possilple instead of the assumed magnitude |/2iQ to take the critical velocity a* and the local sound velocity a. As is known a* = [/(it - 1)/(k + l) J2±q. Substituting -^7 = X,-|_ and — = M we obtain a a K _ 1 _ / (k - 1)M^/2 U=i/ X-L, U= ' ' ' ' ■^ + 1 l/l + (k- 1)m2/2 M= / ^1 (2.5) i/(k+ 1)/2 - (k^ 1)Xi^/2 h. Integral Relations of the Momentum and Energy in New Variables From equations (3.l) and (3.2) we obtain M-Y- 'In order to distinguish various uses of the symbol X herein SLibscripts 1 and 2 have been added by the NACA reviewer in the translated version. ■ 8 NACA TM No. 1229 where p is the density on the hoimdary of the layer (thermal or dynamic depending on which is the thicker). We represent equations (l.l) and (1.2) In the form |_(pua).|-(puv) = p„uu. .|[(...)|] I- (puU) + I- (pvU) - puU« = dx ay Suhtracting the previous equation from the ahove we obtain ^h pg(i_|)l ,2jn;.pu(i-|).|^[p,(u-u)| + uu» p(^^ _ x). xk:.p(i- I). -1^ [(...) 1; From equation (3*2) we find P0= P02(l-U^) 1_ K-1 (U.2) ^_1 tjg-ug -H (T^-l)(l-t7to*) (i^.3) Integrating equation ('+.2) term hy term from y = to y = Ay, if A_ > and to y = B_. if 6 > Ay. (for def initeness we assume that Ay > &„; the same result is obtained if we assume bj > Ay)j making use of the relation (^.3), and taking into account the fact that starting from the boundary of the dynamic layer the velocity u is constant along x and the friction T is equal to zero, we obtain NACA TM No. 1229 "^^f ^H-D-^-hr^r^K-s)^ + uu' /I + u^ - uy -'o uu»(Tv-i) r^ u^ -^0 P 1- dy = T w where (l+.U) V = (^+ €) ^ S7-'y=0 W/w ('+.5) Is the frictlonal stress at the wall. We now represent equations (l.2) and (l.3J In the form 2- (puto*) . I (Pvto') - PU ^ = -— (put*) + T- (pvt*) - pu = .5- &x oy di oy (n + m 5y), and remembering that for Ay > S the heat transfer q = X -r— and the friction t = n g:- are equal to zero on the boundary of the thermal layer we obtain f-Ut * dx ° C^H' (4.6) 10 WACA TM No. 1229 where 1^- Cp (■ f L • (J - .) •. (. % ■-■.(■i„-'-(sf). Is the intensity of the heat transfer at the wall. In solving the problem of the "boundary layer without heat transfer between the gas and the wall for large velocities and P = 1, A. A. Dorodnitsyn introduced the change in variables K-1 (1-U2) dy (U.8) l-u2 Noting that the function under th£ integral sign In equation (^.8) agrees with the expression p/Po2 ^°^ '^ ~ ^' ^® introduce a new independent variable of the analogous equation containing in the function luider the integral sign the expression p/po2 ^°^ "^^^ general case according to equation (3.2) D 1 -u2 + (T„-l)(l-tVto ) For T^ = 1 the relation between the coordinates t) and y depends on t* the unknown velocity profile. For — - = ^ equation (^.9) gives the change in variables applied to the problem of the heat interchange of the plate with the gas flow. In this case the relation between t] and y likewise depends only on the velocity profile. As is seen from equation (U.9) in the general case the relation between the coordinates t\ and y depends not only on the velocity profile u(x, y] but also on the temperature -drop profile t (x, y) which likewise is not initially known but Is determined from the solution of the problem. NACA TM No. 1229 11 Replacing the density p in equations {h,k) and (4.6) by its expression (3.2) and passing to the varlahles x, t^ we obtain + uu» ^ u^ \r^/ u\ uu'(T„-i)PA/ t*\ T^ ^, ; 1 + / (1 - ii) dTi + / 1 dTi = -2- U.IO d_ dx Ut J„ tl Sli- i dTl P02°i (U.ll) where 6 and A are the values of the variable r, referring, respectively, to the boundary of the dynamic and the thermal layers. We denote the thickness of the loss in momentum and the thickness of the displacement in the plane it\, respectively, by '-I'i{^-^)'^ ^* = ^H=/„'(l-S)i'' (^-12) we introduce the concept of the thickness of the energy loss (in the plane xt) ) e = u 5 1 - -^ ^1 (lt.l3) This magnitude has a clear physical meaning; namely, the magnitude 9 characterizes the difference between that total energy which the mass of the fluid that flows in unit time through a given section of the thermal 12 NACA TM No. 1229 boimdary layer would have If its stagnation temperature were egual to the stagnation temperature of the external flow and the true total energy of this mass. The magnitude 6 thus represents In length units referred to the temperatiire to the "loss" In total energy due to the heat transfer. For small velocities the concept of the thickness of energy loss agrees with the previously Introduced concept of the thickness of heat-content loss (reference k). The magnitude .A A = eap = 1 - dTl ih.lh) may he called the thickness of the thermal mixing. With the aid of the magnitudes defined by equations (4.12), (U.I3), and (4.1U) we represent the obtained Integral relations of the momenta and energy (equations (1<-.10) and (l+.ll)) In the final form d0 ^ U^ dx U H + 2 (H + 1) U2 1 -U2 d + U»(Tv - 1) U(l -U2) Hm0 = W 02 (I+.I5) d£ djc u to* e = %r P02^°pto' (4.16) We note that the integration with respect to y (or t]) may be taken from to 09 so that the relations (4.15) and (4.l6) are general for the theory of the boundary layer of finite thickness and the theory of the asymptotic layer. For small Mach numbers (the effect of the compressibility due to the temperature drop) the relations (U.I5) and (4.l6) assume the form «.^(H..,..^(^-.)K,e. ' W "" u \To 7 ^" - PoU2 f . u' ^ ^ to' ^ ^ dx u to > (4.17) NACA TM No. 1229 13 ■vAiere tg = Tq — T^, Tq and Pq are, respectively, the temperature and density of the Isothermal flow outside the thennal boundary layer (it follows from equations (2.6) and (3«2) if we set approilmately U = 0, that is, according to equation (3«5) M = O), The pressure distribution over the profile is determined by the equation of Bernoulli for an Incompressible fluid. ^ As is seen from equations (i<-.15) and (U.l6) and also from what follows, in the variables x, t\ the equations of the system (1.1) to (1.3) Bxe Bimplifled and approach in principle the corresponding equations for the incompressible fluids. For this reason the fundamental methods of the theory of the boundary layer In an incompressible fluid may be generalized to the case of a body in a gas flow with heat Interchange. We give below the generalization of the method of Pohlhausen for the case of the laminar layer and the logarithmic method of Prandtl— Kann^ for the case of the turbulent layer. The proposed method of the solution of the problems connected with heat Interchange pennlts, of course, generalization of certain other problems in the theory of the boundaiT- layer in an Incompressible fluid. II. LAMHIAE BOUNDAEY lAYER WITH HEAT INTERCHANGEE BETWEEN THE GAS AND THE WALL^ 5. Transformation of the Differential Equations Assuming in equations (l.l) to (1.3) e = and t* = T - T^, Bubstitutlng the values p, p, and |i according to equations (3«l) to (3.3)i we transform these equations to the new independent vari- ables 1 = 1 and J], deteimined according to equation (^.9). The equations of transformation of the derivatives will be ^Prcan. equationa (S.l) and (3.5) we have Poo -Po= [i^|(--i)M^]'"^-i PqI Jfi :.,li^,%=JL^, ,] Po«-2-r ^-"^-^-alT whence setting M = 0, we obtain Pq + 5- (pqU^) = Constant *En what follows we restrict ourselves to the case P = 1. Ik NACA TM No. 1229 We obtain (introducing the notation v 02 ^^oo ^02 . . 1 - u^ + T^ - 1)1 - t7to*) dx oil 1-U2 a + ^1 1 _u2 + (T^_l) h.__ n-a l> (5.1) ^ ^ V P02 ^7 (5.2) * dt^ St* St U TT + V u ox Sti iic = y(l-^2f-ll_. 02 Sti 1 -u2 .(5.-i)(i-^^ n-1 ^ ^ (5.3) If it is assumed approximately that n = Ij the obtained system can he still further simplified. 6. Generalization of the Method of Pohlhausen We represent the velocity profile and the stagnation temperature- drop profile hy the polynomials s-i(^H^)^- 1 6 8 - B % = 20 ^^1 -O.U + 0.229c/|j - 0.lU3c/^\ + 0.0290/'- ^ ^^ 5!Z: (1 . u2,«-i •-w R 02 »i|*w-Ki-)'(^-n) Considering this equation as linear in ^U^ we write its solution in the form I B02 1-^ U^(l-U2) 2 1-1+;^ C + r T^^-2 JP-^ (1 -U2) ^^0 ^20(^) °^ "^^® first approximation, making use of \2(x) of the first approximation and (a/6)q (in the succeeding approximations there is used the function X2(x) following and X,2. (x) preceding) . From the values of ^29^^) ^"^^ "^2^^^ ^^*^ *^® ^^^ of the graph there is obtained X2a(^)' ^ those cases where there is a considerable change in the ratio A*/i3 (or the function T^(x) ) the computation must be conducted over segments. The required data for each succeeding segment are taken equal to the corresponding values obtained at the end of the preceding segment. The local Nusselt number (that is, the coefficient of heat transfer q^Ao* reduced to nondimensional form) and the coefficient of friction are found from the equations n K. N = ^w^ K^o* = %r^ 2t Cf = w _ 2 s n-1 PaPo E„ ■•w 1 + I (k - l)Meo^ 1 + 1 (k -1)M„' (1 -u2)^-^ Bl A n (1 K U s (8.10) (8.11) *In particular for T^ = 1 formula (8.5) with (^2)0 "^ ^ gives 8^ 00 l-£ 0.U7 r,c-i 1-^+ -^ U°(l-U2) 2 U^-l(l -U2) 2 K-1 ,_ dx (c = 6) which agrees with the equation of L. G. Loitslansky and A. A. Dorodnitsyn for the computation of the laminar layer without heat trajisfar (reference 6). In the absence of heat transfer and for small Mach numbers we again obtain from this the quadrature (uAj«)6 Jo V^"/ \ n / earlier derived by us on the basis of the method of Karman— Pohlhausen for the laminar layer in an incompressible fluid. (See Tekhnlka Vozdushnogo Flota, No. 5-6, 19h2.) NACA TM No. 1229 23 For grnnll Mach numbers equations (8.5) ajid (8.9) assume the form e^E = ^ f (^)" 2Bi & - 1) ^ X ^ (8.13) (TjTo - 1)^(uAJ„)2 ^0 W V^O / U^ A ■^00 9. Dependence of the Reynolds Kumher R02 on the Parameters of the Flow TaJclng account of the fact that according to the equation of state P02 P02 = we represent the parameter Rno in the form POI Poi ^ n— *r r- ^^-, r-n 2 2(k-1) . P02 ^ /2ioLpoi , , ^02 = ^01 :; — ' where Eqi = (9-1) The parameter Eq^ is expressed directly in tenna of the Reynolds UooLPoo U„ number 'R„ = and the Mach number M^ = — = of the approaching 1^00 aoo flow. From equations (3. 3) to (3.5) ve find K+1 _1 2 (9.2) In the case of subsonic (subcritical) velocities we have Eq2 = Rqj = Eqq. For supersonic velocities the ratio P02/P0I ^^ found from the condition of a line of a flow passing through an oblique shock wave (or a head wave) at the leading edge of the body. Considering each surface of the profile separately we denote by Pq the angle which the tangent to the surface of the airfoil at any point makes with the direction of the velocity of the undisturbed flow and, by 9 the angle which the normal to the surface of discontinuity makes with the same direction. From the equations of the oblique shock wave we obtain Eqi = R„ =^ (1 - U„2) ""-^ ^ R„ 1 + 1 (k - l)Moo' Uqo L ^ 21^ NACA TM No. 1229 p / 1/2(k + 1)M„co32cp V-VSK 2 2 .-^r / > -^ = 5 ( M«,^co82cp i] (9.3) Pqi \1 + 1/2(k - 1)M<„ cos2cp/ U + 1 1/2(k + l)M„,^sin 2cp tan (cp + Po) = i — p 5" (9.^) "^ 1 + 1/2(k - 1)M<„ cos'^q) In the case of a head wave in front of the "body the direction of the velocity after the discontinuity (for the flow line at the profile) may "be considered to coincide vith the direction of the velocity "before the discontinuity; in equation (9.3) there is in this case to "be substituted 9=0. 10. Boundary Layer in the Flow of a Gas with Axial Symmetry For any axial flow a'bout a body of revolution the integral relations of the impulse and energy have the following form: — / ^ pu^r dy - U ^ / pur dy = - ^ 5yr - T^ (lO.l) dx Jq ^0 dx "^ ^J Cppu(t* - to*)r dy = -^^ (10.2) In these equations the usual simplifications were made; x is the distance along the arc of the meridional section, d the distance along the normal to the surface, and r(x) the radius of the cross section of the "body of rotation (the change of the radius vector within the boundary layei is neglected). The boundary conditions of the problem and also the assumptions with regard to the external flow are taken to be the same as in section 1. Setting up expressions for T, p, p, and [i as in sections 2_ and 3 and introducing the new independent variable t] by formula (^.9) we obtain the integral relations of the momenta and energy in the variables x. ti: NACA TM No. 1229 25 dx "^ U H + 2 + (H + 1) U2 1 - U^ U»(Tv - 1) U(l -U2) 0Hqi + yit - d = W POO^ ,U2 (10.3) d9 U' - r^ *0 + -=r + r=r^ + r dx u ^ "'^O* I* %, PQO^S^O ^ X _ d = ^, i3 = -.and so forth) (lO.U) (L Is a characteristic dimension, for example, the length of the body of rotation. ) Restricting ourselves to the case P = 1 and taking the expressions (6.1 ) and (6.2) we obtain a closed system of equations (10.3), (10.1;), (6.9), and (6.11) the solution of which we write (for the case where there is no shock wave) In the fona ^^E 00 1-^ uC(i_u2) 2-2 L 1-^ + 2. , K C + r T^-^tr^-l (1 - U2) ^ ^-1 r^o d5E e^E, 00 U2(T^ - 1)V c» + where (10.5) =s n-1 _o.K-l T^^-"2BiU(l - U2) (T^ - D^r^ ^ dx 2^2 e .,. ^ A (10.6) j_FEooU^(1 1-^ U2) 2r2 x=xo C = [02rooU^(Tw-1)^?^]_ _ x=xo The method of computation does not differ from the case of the two-dimensional flow. For the coefficients of the heat transfer and friction the equations (8.IO) and (8.II) remain valid. In the case of the internal problem (flow in nozzles) the Nusselt number and the friction coefficient are determined by the equations NOO = ^oo'fco* = T. ^ n-1 w (1 . u2)K-l |, Cfoo POO^ 1^00 U5 26 NACA TM No. 1229 vhsre Xqq is the coefficient of heat conductivity corresponding to the tesiperature Tqq. III. TURBULENT BOUKDAEY LAYER IN TEE PRESENCE OF HEAT TRANSFER BETWEEN TEE GAS AND WALL 11. Fundaniental Aeauaiptlons The functions H, Bsjt, t^, and g^ entering equations (4.15) and {h.l6) are determined by equations (4.12), (k.lk), (U.5), and (4.7) which express them as functions of S and 6 through the medium of the velocity profile and the stagnation temperature— drop profile. The present state of the problem of turbulence does not permit representing the velocity profile (and also the temperatujre profile) by a single equation v/hich holds true from the wall to the boundary—layer limit. The fundamental dynamic and thenaal characteristics of the turbulent layer can nevertheless be computed with an accuracy which is sufficient for practical purposes. A fortiuiate property of equations (4.15) and (4.l6) v/-hich can be predicted on the basis of the results with respect to noncompresslble fluids is that the functions H and Hrp change very little oyer the length of the turbulent layer and the functions t^ and q^ connected with -8 and 9 by the equations are little sensitive to the actual conditiona which prevail at a given section of the boundary layer. Hence H and H^ji (and also magnitudes analogous 'to them) can be taken as constant over x and the relations between t^ and -a (the resistance law) and between q_y and 9 (the heat— transfer law) can be set up starting from the assumption that the conditions at the given section of the boundary layer do not differ from the conditions on the flat plate. On the basis of the derivation of these supplementary equations we assume the simple scheme of Karman according to which the section of the boundary layer is divided into a purely turbulent "nucleus of the flow" and a "laminar sublayer" in Immediate contact with the wall. In the latter the turbulent friction and the temperature drop are small by comparison with the molecular. We assume that in the turbulent "nucleus" the frictional stress is expressed by the formula of Prandtl: ^ - "''O <--' where I is the length of the mixing path. In other words, in equations (l.l) and (l.S) we set € = pZ^ ^. It follows directly from NACA TM No. 1229 27 this In view of the fact that the turbiilence ass^xnption of Prandtl gives X^ = c € that the expression for the heat transfer is , dT ,2 d-u dT (11.2) The thickness 5^^ of the laminar sublayer of the dynamic boimdary layer, ecju'al for P = 1 to the thickness Ayj of the thermal sublayer, is determined by the critical Eeynolds number (the Karman criterion) Ut5 ^I^=a^ (a8Sll.5) (11.3) vhere u^ is the velocity on the boundary of the l&minar sublayer, p^ and Hy aj*e the density and viscosity at the wall. 12. Derivation of the Resistance Law Assuming that as in the case of the noncompressible fluid a linear variation of the velocity in the laminEir sublayer is permissible on accoiint of the flmfl.11 thickness, we have ■^w = ^^^ 5 (12.1) 7l From equations (U.3) and (12. l) we obtain (12.2) In equation (l2.2) we pass to the vEiriable r\. Near the wall on account of the smallness of the terms u^ and t*/tQ* we have 7= (l-u2) ^0 hence K 1^ 1_U2.(T„-1) ^-Q 6y,»i„(i-n2r-i5j 1-K dTi » T„(i -u'^r T) (12.3) 28 NACA TM No. 1229 vhere 5^ = A^ is the thickness of the laminar sublayer for the varlahle t\, Further, Substituting these expressions in equation (l2.2) we obtain ^=^1,- (-5^ = $) (12.1.) For the fundamental parameters of the dynamic layer there is here introduced the notation E^ = U^02. ^ - T-^^— rTTP (1-^)^^' ^^ (12.5) /Vpo2 Tw ^ Equation (l2.l) is with the aid of equations (3'2) and (U.9) transformed into the form 3k .2 „ ^2 °^ V^^-^ [l - u2 + (T^ - 1)(1 - tVto^P Since for small t\ the terms u^ and t*/tQ* are small and the mixing path 2 = ky (k = 0.391) vhere the coordinate y ^s expressed according to equation (l2.3), the "generalized" mixing path I near the vail is a linear function of t): ^ = kTi-^(l-U^) (12.7) In deriving the resistance lav in an incompressible fluid a linear mixing— path distribution and a constant frictional stress are assumed for the entire section of the boundary layer, from the wall to the outer boundary. Actually the mixing path increases at a considerably slower rate than according to the linear lav and the friction drops to NACA TM No. 1229 • 29 zero as the outer boundary of the layer Is approached. The assumptions made act In opposite directions and lead to a satisfactory relation "between the parameters E „ and ^ . Carrying over this fundamental idea of the logarithmic method into our present theory we set t = t in equation (l2.7) and assume the linear law (equation (12.7)) for the entire section of the boundary layer. We thus assume that as in the case of the noncompressible fluid there will be a mutual compensation of the errors committed in the distri- bution of T and I. Integrating equation (12.6) between t\ and 6 we obtain the approximate velocity profile: ii = 1 + - m II (12.8) U k^ 5 From equations (l2.l) and (12. U) we obtain the velocity at the boundary of the laminar sublayer 2 _ g U " 5 The condition of the equality of the velocities of the turbulent and laminar flows on the boundary of the sublayer gives Eg = C^T^^e^^k^ MRg = U5Eq2, C^ = f ^~^°' = 0.326J (l2.10) Making use of the velocity profile (12.8) in equations (1+.12) we obtain Eliminating from equation (12. lO) and the first of relations (12. ll) the auxiliary variable 6, we obtain the resistance law: E, = CiT/e^^ C"ft) ^^^'^^^ We obtain incidentally also the approximate expression for the parameter H : 5 1 / » H = — = (12.13) ^ 1 - 2/k^ 30 NACA TM No. 1229 13. DerlTation of the Heat-ITransfer Law In this section we shall give a generalization to the case of a gas moving with large yelocities of the heat-transfer law earlier derived ty us (reference h) for an inconrpressihle fluid. We construct the function dt* q*= X^= q + iru (I3.I) dy J For the turbulent nucleus of the flow we have dt* dt* „ ,2 du dt* ^^ ^ U.U an, ,kf au ax (to r,\ 1 = H TT" = Cp€ = CppZ ;- (13.2; '' dy i' dy ^ dy dy Transforming this equation to the variable t] we obtain du dt* ~2 ^ jf (^ _ ^2f-'i- ^^ <^^ ' [l-u2 + (T^-l)(l-t*/to*J^ (13.3) Near the wall the function q* behaves like q, that is, differs little from the constant value q^., and the mixing path I depends linearly on f] according to equation (12.7). The common mechanism of the transfer of heat and the transfer of the momentum in the flows along solid waJJLs provides a basis in the derivation of the law of heat transfer for assuming as before a constant value q* = q„. and the linear law (equa- tion (12-7)) for the entire thickness of the thermal layer. Substituting the sxpression for du/dT) obtained from equation (12.8) and integrating equation (13- 3) from ti to A we obtain the approximate profile for the stagnation temperatures = 1 f —^ In J (13.4) r Is w *0* c_,to*T„kC NACA TM No. 1229 3I From equation (13.I), assuming a linear distribution of the stagna- tion temperatures in the laminar sublayer, we find — = — (13.9) ^ V n VkC^ ^2^^^' A k^^ A From equations (l2.10) and (13.8) it follows that | = exp(k^^ - kt; ) so that we have ^i \ hJ i-til^-—^ (13.10) 32 NACA TM No. 1229 Eliminating from equations (13.8) and (13.IO) the auxiliary parameter A we obtain the heat— transfer law •■(' Kq = CiT^^ fl - -^ exp k^^, (13.11) We obtain incidentally alao the approximate expression for the parameter Hrp: iMt ■ % = (13.12) l/k^d - 2/kCT) l4. Solution of the Equation of the Turbulent Dynamic Boundary Layer We represent equation (k.l^) In the form We make the change in variables (reference T)^ z = e^^d -2M)k2^^ (11^.2) Differentiating this relation with respect to x and using equation (12,12) we obtain dx \K^ dx T^ dxy \^ 1 _ 2/k5 + 2/k^^y NACA TM No. 1229 33 From equations (1^4-. l) to (1^4-. 3) we obtain dz U»K(H + 1) U«E(Ty - 1) A* ^ T^» ^^™Qg^ ,, r^\K-l /., , n (Uoo - ^J ^^=^oo-~Z^l(-^j^. = Poo^» (16.1) viiere \ ^ denotes the sum of the momentum-loss thicknesses referred to the upper and lower surfaces and computed at a great distance from the wing where 6 — ^oo and U — >Uoo. For the drag coefficient we have 2Q ■'xp - 2 PoJJoo L = 2y v^cc [l + I (k - l)M, K-1 (16.2) NACA TM No. 1229 37 The problem confllsts In expressing iSoo i^i terms of the dynamic and thermal characteristics of the houndary layer at the trailing edge. Since in the wake behind the body j^ = and q^ = 0, equations (U.l6) and {h.l'j) for the wake assume the form ^5-)'- d-d -n* f B. + Jfi „ D I- , ^ ^ di xj t^* djc We introduce the notation ^.Ela.A^e^o (16.1.) ,_, H + U^ Tv - 1 / ^ ^ G(x) = ^ + -^^7% (16.5) 1 - IF 1 - IT ^ and represent equation (16.3) in the form l^ = _(2 + G)i-lz.^ (16.6) ^ dx dx Uo. Integrating this equation with respect to x from the trailing edge (denoted by the subscript l) to i = 00, we obtain ln=S2.= (2 + Gn)ln=i+/ ln=-dG (16.7) For U, s; 0, ^ = 1 the function G^x) goes over into H(x). For ein incompressible flxiid however the hypothesis of Squire and Young (reference 8) on the linear character of the dependence ln(U/croo) on H holds : ln(uAjJ _ In(UiAJoD) H« - H ^ - H, 38 NACA TM No. 1229 Making the analogous assumption ln(u/Uoo) ln(Ui/aoo) G«,-G G-»o — Gr]_ (16.8) we obtain"^ (16.9) We write down the expression for G-|_: % + Ui2 T - 1 Gi = ^p- + --h^ -^ \ (16.10) 1 - U^^ 1 - U^ ^1 It is easily seen that Hoo = 1 and Hm^ = 1, hence G^= ^ + " . ^ (16.11) * 1 - U„^ 1 - U„2 ^„ ^The same result can "be arrived at from the following elementary considerations. Equation (16.7) may he represented in the form In ^ = (2 + Gi) In rA + (Goo - Gi) In =» ■^1 Uc Ugg where Uj^ is a certain mean value of the velocity IJ that lies hetween U2_ and IJ„. For the usual profile shapes however the ratio Ui/Uoo Is^ in general, near unity and since the magnitude 2 + Gri exceeds the magnitude Gw — _Gi hy several times, therefore for any choice of the mean value of U^^ the relative error in the determination of i3^ Is not large. Taking the geometric mean Uj^ = j/u^Uoo we again arrive at equation (16.9). NACA TM No. 1229 39 Eeplacing In equation (16.9) Grj_ and G„ by their values, we obtain finally ?„ = ^t( =ri) (16.12) '.(» K + 5 Hi + 1 ^^2 u«2 ^ / _ i)ht 0i/^\ (t^^ - l)e„/^% Tt = -^ + -— + TT + — T + # ^ nTT^T_TT'-2 -, XT '- '- TTT^ 1-U-," 1-U„ "^ 1-U-," " 1-Uc -"1 -^ - ^00 X - u^ '00 From equation (lO.il) it follows that 6U(Ty — l) = Constant, hence (^ - 1) e„ = (T^ - i)ei -A (16.13) ' ^ ' 1 u, CO For small Mach numbers equations (l6.2), (16.I2), and (16.I3) assume the form 00 --'©■ &-^ ^- = ^Un"J' i^-v ^- = (v-^'^^ 17. Boundary Layer in a Gas Flow with Axial Symmetry For the turbulent flow about a body of rotation the equations (lO.l) and (10.2) in the variables x, y and the transformed equations (IO.3) and (10. U) remain valid. Eestricting ourselves to the case of the Prandtl number P = 1 and introducing the parameters E^, ^, Eq, and tj^ we represent the integral relations in the form ko NACA TM No. 1229 dx U(l-U2) _ — ^^ T Rs + — ^ ^^^o(i U2f-1 (17.1) dE, iz cLt^* ."iB,._-i--^E, = ^i-i5Hoo(l--^)«- to* da (17.2) T w Making use of the drag law equation (12. 12), the heat-tranefer law equation (13.II), effecting the change in variahlea assuming the little changing magnitudes H, K, K^ constant with respect to X and also a constant mean value for the ratio — = h, we obtain 5 -a a system of linear equations the solution of which has the form z = /(1-ug)' ^nEyC^ C + -"o^^^^'-^-^^^a-i^F^ ^1 Jxo /(1-U2) ^9\c (17.3) C = z^v^ nK /(1-U2)° x=xo Zrp = ^^nKT^T(T^ _ 1)% C + ^1 ^io _^n&i.^l(^ - 1)^ -1(1 - Vi^)^-h^ d5 K z^ff. 5„'^(T„-l)^r^' -'X=Xr NACA TM No. 1229 1+1 For the frictlonal stress and the Nusselt number, equations (lk.6) and (15.5) remain In force. In the case of the internal problem ^00*0 "T ^^ POO^ K NOO = ^^ = 77- r ^00^(1 -^r\ C,oo = -^ = ^ :^ (1 - T^^ f-^ (17.5) The theory presented, in particular the integral relations of the momenta and energy established in part I, permits determining the thermal and dynamic characteristics of the boundary layer at a curved wall in the most general cases, that is, in the presence of ertemal and internal heat interchange. The computation of the boundary layer by the equations derived in parts II and TTT on the assumption of the Prandtl number P = 1 permits finding directly for arbitrary Mach numbers (excluding the interval from *^ = ^^ to M^ = l): (1) The coefficients of the heat transfer from the wall to the gas for a given maintained temperature of the wall through heat supplied outside the body and the coefficients of heat transfer from the gas to the wall, that is, required for maintaining the heat conduction within the body at the given temperature of the wall. (2) The distribution of the frictlonal stress eO-ong the wall and the profile drag of the wing (in the case M„ < M^o ) for arbitrary cr ratio of the stagnation temperatures and those of the wall. For small velocities the obtained equations express the dependence of the heat transfer and the drag on the ratio of the absolute tempera- tures of the flow and the wall (the effect of the compressibility and the change of the physical constants due to the heat interchange). In conclusion we give the results of computation of a single example. In figure 3 is given the distribution of the velocities of the external flow for the supersonic flow about a body with two sharp edges. The contour of the body and the position of the discontinuity are also shown. The flow was confuted by the method of Donov (reference 9). In figure h are given the curves for the Nusselt number N which assure the uniform cooling of the surface up to the temperature T^. = 0.25Tqq for E„ = 15 X 10°, Meo = 2, and Mo, = 6 for the laminar (lower curves) and turbulent (upper curves) regimes. Translated by S. Eeiss National Advisory Committee for Aeronautics 42 NACA TM No. 1229 REFERENCES 1. Dorodnitsyn, A. A.: Boundary Layer in a Compreasi'ble Gas. Priklalnaya Matematika i Meldiajiika,. vol. VI., 19^2. 2. Frankl, F. 1., Chrlatianovich, S. A., and Alexseyev, E. P.: Fundamental a of Gas Dynamics. CAHI Report No. 36k, I938. 3. Kalikhman, L. E. : Drag and Heat Transfer of a Flat Plate in a Gas Flow at Large Speeds. Prikladnaya Matematika i Mekhanika, vol. IX, 19^5. k. Kalikhman, L. E. : Computation of the Heat Transfer in a Turtulent Flow of an Incompressible Fluid. NII-I Report No. h, 19^5. 5. Lyon, H. : The Drag of Streamline Bodies. Aircraft Engineering ^ No. 67, 193^. 6. Dorodnitsyn, A. A., and Loitsiansky, L. G. : Boundary Layer of a Wing Profile at Large Velocities. CAHI Report No. 551^ 19hh. 7. Kalikhman, L. E. : New Method of Computation of the Turbulent Boundary Layer and Determination of the Point of Separation. Doklady Akademii Nauk SSSR, vol. 38, No. 5-6, 19^3. 8. Squire, H. Bo, and Young, A. D. : The Calculation of the Profile Drag of Aerofoils. ARC, R & M No. I838, 1938. 9. Donov, A. : Plane Wing with Sharp Edges in Supersonic Flight. Izvestia Akademii Nauk SSSR, Ser. Matematichoskaya, 1939, pp. 603-626. NACA TM No. 1229 h3 U^ Compression shock Figure 1, 2 1 / It- / 6 k 7 . / '~\ r / ./ >< V L X \ Too t 2 t 3 f S Figure 2. 'i^o^^^M^-e DZ 0.4- 0.6 0.8 I.D Figure 3. 7 6 5 f J 2 \ ?25 \ 4= \^ \ \ \ ^M^^Z \ \ V \ r V \ N \^ V ^^ ^^ 0.2 O.if- 0.6 0,6 X Figure 4. 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