CO CO CO En < S3 NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS TECHNICAL MEMORANDUM 1333 ON ROTATIONAL CONICAL FLOW By Carlo Ferrari Translation of "Sui Moti Conici Rotazionali" in "Onore di Modesto Panetti" published by L'Aerotecnica, Associazione Tecnica Automobile., and La Termotecnica, Turin, Italy, November 25, 1950 Washington February 1952 ' ^ITY OF FLORIDA LIBRARY] ' 1 us v ^c/7w'/^~ NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS TECHNICAL MEMORANDUM 1333 ON ROTATIONAL CONICAL FLOW* By Carlo Ferrari SUMMARY The author determines some general properties of isoenergetic rota- tional conical fields. For such fields, provided the physical parameters of the fluid flow are known on a conical reference surface E, it being understood that they satisfy certain imposed conditions, it is shown how to construct the hodographs in the various meridional semip lanes, as the envelope of either the tangents to the hodographs or of the osculatory circles . ANALYSIS 1. A method for determining the field of flow about a cone of revo- lution, the axis of which is aligned with the direction of the impinging supersonic stream, which is taken to have a uniform velocity distribution sufficiently far ahead of the body before the conical field is created, was developed by Busemann (reference l) at an early date. Several years later the present author (reference 2) extended Busemann's procedure to cover the case of a cone of any shape whatsoever situated in the flow, so that its axis was at any arbitrary finite angle of attack; that inves- tigation was confined, however, solely to irrotational conditions. With proper alterations, nevertheless, this treatment of the yawed arbitrary- shaped conical surface can be applied to the case of rotational flows. The purpose of the present investigation is just to give the relationships which permit one to draw the hodographs for the flow, in reference to the various meridional planes through the body axis, in the case where the motion is defined by a rotational field of conical flow with arbitrary specification of the cone shape. 2. Upon the mere assumption of isoenergetic flow in a perfect fluid, one may write the equations of motion in the form (reference 3): Original Italian Report appeared as Sui Moti Conici Rotazionali in Onore di Modesto Panetti , published by L'Aerotecnica, Associazione Tecnica Automobile, and La Termotecnica, Turin, Italy, November 25, 1950. curl V x V = ii- grad S 7R B NACA TM 1333 div -/) 1 Mi v = (1) wherein R is the universal gas constant, 7 is the adiabatic exponent, V^ is the limiting velocity obtained when the flow expands to a vacuum, C is the velocity of sound, S is the entropy, and V is the fluid velocity. Upon employment of a spherical coordinate system (r,0,cp), as depicted -* curl V in figure 1, the components of are taken as w r , w©, and vq; where w r is the radial component, Wm is the component lying in the meridional plane and normal to the radius vector, while w@ is the com- ponent that is perpendicular to the meridional plane. Likewise, the corresponding components of v/Vj are denoted by v r , Vm, and Vg. Between these components there subsist the following relationships sin cp cVm b(v e sin cp) be o? = rw r Sr sin 5v T cp be = rw, cp (2) bv-r S(rv ( Sep cp, rw Based on the assumption that the flow is conical, the following scalar equations are derived in a straightforward way from the first of the equations (l): NACA TM 1333 w 9 v cp " w cp v " ° c 2 V m W„ + WmV,, = *cp»r "cp v r " 7R r sin ^ bQ (3) v Q w„ - vv a = ■? 1 c 2 d s wherein c 2 = C 2 /Vj 2 . The set of equations (3) are not independent of each other as is evident from consideration of equation (l) directly, but they are inter- related through the expression V x grad S = (h) which, for a conical field, becomes SS = _ V0 1 SS t^,\ Sep v cp sin cp $e From the second of equations ( l) , upon use of the hypothesis that the flow is conical, and by taking into account the relationships expressed by equations (2) and (k 1 ), one then obtains that VV V ,^A = ^L_V^_ cotq) v m L c*p / " sin cp c 2 S9 * \ c 2 \ . *£)L + -i- *£\ - 31 » „ ZBBlr ^ (5 ) , c 2 / V sin cp d6> / 7R ctp c 2 This expression differs only by the presence of the rotationality terms from the analogous relationship derived in reference 2 previously mentioned. k NACA TM 1333 3. By means of equations (3)> (M, and (*+') one may deduce some interesting properties of conical fields. Let it be assumed that one of the stream surfaces of the flow is conical (this will be the case for a field of flow arising by the action of a uniform supersonic stream impinging from any direction whatsoever upon a conical-shaped obstacle); it will be convenient to designate this surface as Z c . Let the versor of any arbitrary general one of the generatrices of the conical sur- face Z c be denoted by r, then grad S x r = 0. On the other hand, if the versor of the tangent to any streamline whatsoever that is traced upon the surface of the cone L c is 1 denoted by t then it is true, in addition, that grad S x t = 0. It is evident, therefore, that grad S is perpendicular to the surface Z c ; that is, the above-described conical surface is a surface of constant entropy. Besides, let it be assumed that the conical flow is symmetric with respect to the meridional plane 9 = +90° (this will be the case already mentioned for the field of flow about a conical-shaped obstacle). At all the points of this plane it is true that vg = 0. One then deduces, upon the basis of the first of equations (3), that wg = provided that v,p is not zero everywhere. On account of this, and through utilizing the third of equations (3) it follows that — = 0. Thus even dp the meridional plane of symmetry for the conical field is itself a con- stant entropy surface, and at this plane the flow is irrotational as is easily deduced upon taking cognizance of equations (2J~ I In conjunction with the result obtained above one can derive from this latter fact that, for the case of flow about a conical obstacle, the shock wave in the two semiplanes 9 = 90° and 9 - -90° must produce the same change in direction of the stream velocities; and so the tangents to the trace of the shock wave in these semiplanes are symmetrically inclined with respect to the undisturbed stream velocity vector. Now let us consider an obstacle in the form of a right circular cone. Upon the surface of this cone it is true that — = Vm =0, and therefore one ~b9 gets that Wm = . Thus the following relationship results 1 Sv r ic\ v e = - (6) sin cp de NACA TM 1333 ! On the cone one can always express the v r values as a periodic function of 6, and thus v r = B + £ B n sin n0. It follows that on the cone's surface the peripherial velocity component is given by L B n n cos n© sin cp just as in the case of irrotational flow. Now, if we let the angle of incidence of the axis of the cone he denoted by B, then the expression for v r becomes simply v = B + B-, sin 9 if only terms of the order of magnitude of 3 are taken into account. Since this is true, then because B-^ is proportional to 3> the B n o coefficients have to be at least as small as 3 • The relationship given by equation (6) may be generalized for the case of a cone of any shape whatsoever. It is assumed for this purpose that the cone's surface is divided up by a network of orthogonal coordi- nate lines a^ and Op (r = const, and cp = const., respectively). The former of which are the intersections of the spheres with radius r upon the cone under consideration, while the latter are the generatrices of the cone itself. At an arbitrary general point P on the cone the length of the linear element dcr-^ can be written as: da^ = rh-^ ( 0") &6 while the length of the linear element dap along the line <7p is given by: dap = dr. The component, in the direction of the normal to the cone at the point P, of the curl is n rh x c>r V 1 1 J dvp where v-^ and vp are now the velocity components in the direction of U]_ and Op, respectively. On the other hand, upon referring to the first of equations (l), it is still true that w n = , and on account of this it is evident that: NACA TM 1333 1 hi 50 If the component of velocity in the direction of the radius vector is expressed as a periodic function of 0, as is still permissible, then equation (6 1 ) immediately furnishes the means of obtaining the corre- sponding expression for v^. k. It is now easy to determine how to continue the construction of the flow field downstream of a given conical reference surface, Z, upon which the physical conditions of the flow are assumed known. Let the equation of the conical reference surface, £ , be given by From the relationship
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